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Craving Earth: Understanding Pica--the Urge to Eat Clay, Starch, Ice, and Chalk

Sera L. Young

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Paper, 240 pages, 20 halftones, 16 line drawings, 3 tables
ISBN: 978-0-231-14609-8
$22.50 / £15.50

February, 2011
Cloth, 240 pages, 20 halftones, 16 line drawings, 3 tables
ISBN: 978-0-231-14608-1
$65.00 / £45.00

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“Every day, twice a day, I take a chunk of earth from this wall and, well, I eat it.”

Had I understood Mama Sharifa correctly?

We were sitting on a woven palm mat, in the only shade in her sunbaked yard, on a tiny Zanzibari island called Pemba. There were three of us: Mama Sharifa, Biubwa (my research assistant), and me. Our backs were against the dirt wall of her outdoor kitchen, our legs stretched out in front of us, discussing the things she eats during pregnancy.

With raised eyebrows, I looked to Biubwa to confirm that I had indeed understood her Swahili. Biubwa nodded. “Yes, she is saying she eats earth.”

“But why?” I asked.

Mama Sharifa bent at the waist as much as her pregnant belly would allow to idly slap at a fly on her ankle. Then she looked away from us. “I just eat it, that’s all.” Her pink and orange kanga , a light cotton cloth frequently worn as a head covering, shifted over her shoulder and obscured her face, and I feared she would say no more on the matter.

But after a long pause, her arm reached out from under her kanga. She turned toward us, plucked a chunk of earth from the highest part of the wall she could reach, and displayed it in her open palm. I looked from the chunk of earth in her hand to her face and then back to her hand.

I smiled at her and repeated my question. “But why, Mama?”

She was giggling by then, out of what I’ve come to recognize as a combination of embarrassment and sheer inability to answer this question. She brushed at some dust on her long skirt, then stared off into the distance again. And then she locked eyes with me.

“I don’t know. I really don’t know. I just do it.”

She offered the earth to me, and I took it. First I smelled it. Then I touched it to the tip of my tongue. Then I nibbled into it. It tasted bland, like old air. But after I swallowed, my tongue felt different, dried out, as from the astringency of tea that has been brewed for too long. A few grains of sand remained in my mouth for the rest of our interview. We moved on to other topics.

But for the rest of that research period on Pemba, and for the many that have since followed, I learned as much about earth-eating as I could. I asked pregnant women about their motivations. I quizzed fellow passengers on buses. I asked the old men drinking Arabic coffee at dusk. I probed nurses in the antenatal clinics. What other non-food items did people crave? Did all pregnant women have these cravings? Was it only pregnant women? Did anyone know why they did it? Where did the idea to eat these things come from? Is it some sort of religious phenomenon? Which earth is the stuff for eating? However, my pestering raised more questions than it answered.

During another interview that summer, the responsibility for understanding pica was unexpectedly shifted to me. I asked Mama Khadija, the second wife of a traditional healer, if she knew why people eat earth.

Uhh, no, I don’t know.

Do you have any ideas about why some people sometimes eat it?


Are you sure?


Not even one idea?

This time, she didn’t reply but just looked at me, smiling slightly, shaking her head as one does with an incorrigible child. I sheepishly apologized for asking so many questions. But she then said something that changed the trajectory of my academic pursuits. She pointed at my clipboard and recorder and said, “Since you’re the researcher, why don’t you find out and tell us?”

And with that, dear reader, our adventures with pica begin.

Chapter 1: What on Earth?

Mama Sharifa eats chunks from the earthen wall of her outdoor kitchen in Zanzibar, while in Washington, D.C., Pat crunches through a ten-pound bag of ice from 7-Eleven every day. In New Delhi, Simran starts her morning with a handful of uncooked rice, and in Mississippi, Tanya eats Argo cornstarch, but only after her husband has gone to work. In Guatemala, Carlita nibbles little blocks of clay with a Virgin Mary pressed into them, while in California, D’angela buys ten boxes of chalkboard chalk for snacking whenever she can get to a Walmart. What is the common denominator? These are all instances of pica.

Pica is the scientific term for the craving and subsequent consumption of non-food items. It’s not an acronym, or an abbreviation, or a famous physician’s last name. Pica pica is the genus and species of the common magpie. Magpies are frequently seen with all sorts of items in their beaks, from chewing gum wrappers to wire hangers. Because of their attraction to sparkly objects, they were thought to be birds with an indiscriminate appetite. (As it turns out, they don’t swallow these items; they build their nests with them.) By analogy, the human condition of desiring non-food items was given the name “pica” in the sixth century (Aetius of Amida/Ricci 1542 [1950]:20). I use the term pica to mean the craving and purposive consumption of items that the consumer does not consider to be food for more than a month (Young 2010).

Pica is not the only name for this behavior, however. Eating non-food items has been referred to in many ways in the two thousand years that people have been writing about it. Some terms are very arcane. Citta , for example, is one term that Galen used for pica; it is Greek for ivy, but may be a misspelling of kitta , which is Greek for magpie or jay (Weiss-Amer 1993). Other general terms that have been used as synonyms for pica include cachexia (Liebault 1598), cachexia Africana (Chisholm 1799), chthonophagia (Dors [Dons] 1838), hapsicoria (Motherby 1785), mal d’estomac (Thibault de Chanvalon 1761), malacia (Liebault 1598), and paroroexia (Ruddock 1924).

Pica is a general term, and in modern medical literature eating non-food items is frequently referred to in more specific ways. Names for specific types of pica generally have Greek origins. They combine the names of specific substances, e.g., “geo” (earth), “amylon” (starch), and “pagos” (ice), with “phagein” (to eat), thus yielding geophagy, amylophagy, and pagophagy (Coltman 1969).

The Pica Substances

Earth is the most commonly craved substance, but it is far from the only one. In fact, the list of pica substances is very long. In roughly descending order of frequency, it also includes cornstarch, ice (if consumed in large quantities), chalk, charcoal, ash, flour, newspaper, toilet paper, paint chips, used coffee grounds, baby powder, and paint chips. While this list may seem highly heterogeneous, there is one commonality. With the exception of ice, all of these substances are dry, powdery, and adsorptive (see adsorption), and most of them are rather crunchy.

Just as we now know that the magpie’s appetite is not indiscriminant—those non-food items in their beaks are housing materials, not lunch—pica cravings are not indiscriminant, either. People regularly go out of their way to obtain items that have the precise odor, texture, and taste they desire, as you’ll see in the following descriptions of the three most frequently craved pica substances.

Earth (geophagy)

Humans have been consuming earth for a very long time. There is good evidence to suggest that we were even eating it two million years ago, when we Homo sapiens were still Homo habilis (Clark 2001:659–62; see also Appendix A, this volume). Earth is consumed in many forms and comes from many sources including mud from a riverbed, broken bits of pottery, earth clods found among dry pinto beans. The amount consumed daily varies, but quantities of 20–40 g are typically reported (Geissler et al. 1997; Luoba et al. 2005; Saathoff et al. 2002; Young et al. 2010b), Most of the earth consumed is rich in clay (Young 2010); although clays may seem unremarkable, they have amazing properties that are discussed at length in chapter 3.

But not just any earth will do. People go to extreme lengths to obtain the earth of their heart’s desire. They may be secretive about the whereabouts of their clay pit (Silverman and Perkens 1966), walk many miles to the site with “good dirt” (Dickens and Ford 1942), tussle with the cattle who are also eating “their” clay (Hunter 1993), and implore relatives to mail boxes of clay when they move to a place with unappetizing soil (1967; Dickens and Ford 1942; Frate 1984). The smoothest soils (i.e., those high in clay content) are the most sought after, from the Arctic (Richardson 1851:191) to the Amazon (von Humboldt et al. 1821, pt. 2, pp. 639–64), and everywhere in between. Sandy soils and soils high in dark organic material, called humus, are typically avoided.

The smell of earth is an important criterion for soil selection the world over over (e.g., Forsyth and Benoit 1989; Hooper and Mann 1906; McIntyre 2000). The earth’s smell after rain, called petrichor (Bear and Thomas 1964), is a particularly important indicator of its suitability. During ethnographic interviews, women’s mouths would literally water as they described to me the appealing smell of freshly moistened earth.

Another criterion for geophagists is that their dirt be “clean.” Most earth for consumption is collected from places where animals do not tread (and therefore cannot defecate), such as from areas high up on a wall or the interior of a well; others insure the hygiene of their earth by drying and/or heating it, either in the sun or over open flame (Young et al. 2007).

One of the stories that best illustrates the acuity of geophagists’ selectivity involves a geophagic wife, a devoted husband anxious to avoid trouble, and police surveillance in Memphis, Tennessee (Finger 1993). The wife sent her husband to get her some clay from her favorite riverbank. She did not want to go because police had been staking out the site, suspicious of the many small holes dug into the bank. But she just had to have some. He dutifully left the house and returned with a bag of earth for her. When she opened it, she knew immediately that it was not from her favorite riverbank spot. She sent him right back out for earth from the stakeout riverbank.

Earth-eating is far more common than just a few cases here and there. Estimates range from less than 0.01% among pregnant Danish women (Mikkelsen et al. 2006), to 5.2% among pregnant Pembans, to 56% among pregnant women in coastal Kenya (Geissler et al. 1998b); Appendices B and C summarize studies of the prevalence of different types of pica among representative samples of pregnant women and children, respectively.

Commoditization is a great indicator of demand, and yes, geophagic clay is now for sale. In fact, there is enough demand across the United States that Sam’s General Store, a shop in White Plains, Georgia, that sells geophagic earth, has established an online presence ( They sell earth in two-pound increments, marked as “a novelty item” (probably to avoid any lawsuits). And just in case you are worried about what the postman may think, their deliveries arrive discretely in unmarked cardboard boxes.

Sam’s General Store sells kaolin, which many geophagists consider to be the most desirable type of clay. However, there are many types of earth eaten, and almost as many names for it. For example, on Pemba Island, where I first learned about geophagy, people eat four types of earth. Their Swahili names are udongo , ufue , vitango pepeta (also known as vitango mlima ) and mchanga . In other places, the variety of geophagic soils is even greater (e.g., Vermeer 1971).

And where does geophagy happen? We know for sure that it occurs on all six inhabited continents (Hooper and Mann 1906). Our best information about the worldwide distribution of geophagy comes from ethnographic literature, i.e., reports from anthropologists, missionaries, and explorers. I have assimilated data from 367 such reports of geophagy, and it is clearly ubiquitous; the methods for this analysis are described in chapter 2. The worldwide distribution of pica is discussed in greater detail in chapter 9.

Raw Starch (amylophagy)

These days, it’s easy to think of starches as a food group to avoid, thanks to the demonization of carbohydrates by the infamous Atkins diet. But take a look at any USDA food pyramid and you’ll see that starches—rice, breads, and tortillas—ought to provide the bulk of our calories. Uncooked starches, too, have a place in our daily lives, although they have little to offer us calorically. Even so, they play a role in our cuisine. They thicken Thanksgiving gravies, give lightness to Christmas shortbread, and prevent powdered sugar from caking.

Raw starches have another function, one that is germane to pica: they sate extraordinarily strong cravings. Until a few decades ago, raw starch was available in most grocery stores in two different products, both of which were attractive to amylophagists. There was cornstarch, mostly used for thickening foods, and there was laundry starch. In the 1960s, before the convenience of spray starch and the magic of wrinkle-free fabrics, if you wanted unwrinkled shirts you needed laundry starch. Back then, laundry starch, which can be made from corn, wheat, or rice starches, was sold in big chunks. When it came time to do the starching, these chunks would be dissolved in warm water, laundered clothes would be dipped into the solution and, once dry, they would be ironed. Besides nicely crisping your collars, it was handy for preventing stains: daily grime would bind to the starch rather than to the fibers of the cloth, making it easy to rinse out.

Many women seeking substitutes for earth that is no longer available have turned to starch as a replacement (e.g., Associated Press 1988; Hertz 1947; McIntyre 2000; Vermeer and Frate 1975). This was particularly common in the mid-1900s among black women who moved from the southern United States to industrial areas like Chicago and Detroit, where the earth they desired was not available. A photograph of a Washington, D.C., resident, in which she and her giggling young son pop chunks of starch in their mouths, appeared in a 1967 Time magazine with the caption: “As good as clay any day.” (Even Argo suggests how its starch may be substituted for clay, albeit not for human consumption. On the outside of some Argo starch packages, there is a recipe for “Play Clay” in which Argo is the main ingredient.)

For many women, though, starch is not a mere substitute; it is the most desirable substance. An enormous variety of raw starches are craved and consumed around the world, including uncooked rice (Giudicelli and Combes 1992; Kettaneh et al. 2005; Posner et al. 1957; Roselle 1970; Young et al. 2010a), wheat, cassava, and rice flours (Kraemer 2002; Levacher 1840; Ward and Kutner 1999), and raw starchy vegetables including potatoes and cassava (Johnson and Stephens 1982; Libnoch 1984). However, at least in the United States, cornstarch once reigned over them all.

That reign has been curtailed, due in large part to the untiring efforts of Dr. Gerald Deas. Dr. Deas is an animated, hands-on physician who still makes house calls and cares seriously about public health: think Cliff Huxtible meets Florence Nightingale. In the 1960s, when he was interning in a Brooklyn obstetrics clinic, he noticed that a lot of black women, “maybe 99 percent,” were eating starch (Cleaton 1983; Day 2000). Dr. Deas explained to me that “in those days, starch was typically stocked in the snack aisle of the grocery store, along with cookies and candy.” He, like many, believed that eating starch caused iron deficiency, and so felt compelled to reduce its prevalence. He was also concerned about the weight gain associated with eating large quantities of starch: one box of cornstarch contains 1,680 Calories, and some women eat as many as three boxes in a day.

So, Dr. Deas became a one-man campaign to educate women about the dangers of starch-eating. He helped to produce pamphlets with catchy, community-friendly slogans that were distributed by the National Urban League: “If you eat laundry starch, you’ll become a stiff?”; “Eating laundry starch from a box is as nutritious as eating rocks”; and “The main thing is what is that package of starch doing to your package [fetus]?” He wrote columns in local newspapers and appeared on radio shows and news broadcasts to discuss the dangers of starch-eating.

His public-awareness campaign efforts paid off tangibly in the reform of the packaging and marketing of starch. In 1977 the director of public relations at Best Foods (which produces Argo starch) sent him a letter stating that “the next order of their packaging material will have ‘Not recommended for food use’ prominently displayed on the front panel.” Several years later, Best Foods made a second modification to Argo starch, one that morphed it into the product found on grocery store shelves today: they began to sell Argo starch in a powderized form. This was a significant blow to pica enthusiasts. The hard chunks of starch were extremely appealing both because of their crunchy texture and the handiness of stowing them in a purse or innocent-looking paper bag (Edwards et al. 1959; Richardson 2002).

Although Dr. Deas has done much to halt amylophagy in the United States, there is evidence that it continues today. Currently on YouTube there is a fascinating video of Suerenity, a very pretty and very pregnant woman, eating cornstarch straight from the box. And if you join the Cornstarch Discussion Group on Yahoo! Groups, you will see it is filled with women “freaking out” over their “addiction to this starch.” Here’s a typical response to a new member who introduced herself by explaining she had been addicted to cornstarch and baby powder for the last fifteen years. “Honey we all eat starch, or baby powder, or baking soda . . . some kind of something strange in this group lol. You be reading a lot of stories about those things. I personally love starch and have been eating it for 10 yrs now. . . . . . . . WELCOME HOME LOL!!!!”

A number of population-level studies of amylophagy from the last few decades corroborate these anecdotes (cf. Appendix B). In a study among 361 rural Mississippian women, 39% had eaten laundry starch (Ferguson and Keaton 1950). In East Texas, one-third of the 150 women interviewed had eaten starch or clay during at least one pregnancy (Taylor 1979), and of nearly 1,000 randomly selected pregnant women in Chicago, 35% had eaten starch (Keith et al. 1968). In our own study of 2,368 pregnant Pembans done in 2004, 36% had eaten uncooked rice in their current pregnancy (Young et al. 2010a).

The amount of starch typically eaten has not been well measured. There are reports of women eating several boxes of cornstarch a day (1967; Allan and Woodruff 1963; Roselle 1970; Warshauer 1966), but on Pemba, for example, the mean amount of raw rice consumed daily was only 26 grams, less than a palmful (Young et al. 2010a).

Ice (pagophagy)

Ice is another common pica substance. Now, don’t think that you practice pica because you crunch the ice in your glass of Coke; a few cubes here and there is not pica. Pagophagists are people who love ice, crave ice, and need ice, and consequently, eat a whole lot of it. How much is a lot? The amount of ice they consume per day ranges from several glasses (Reynolds et al. 1968), to several ice cube trays (Brown and Dyment 1972; Moss et al. 1974; Osman et al. 2005), to several bowls (Sontag et al. 2001; Speirs and Jacobson 1976), to several pounds (Coltman 1969; Cooksey 1995; Haanen and Tan-tjiong 1982).

While the written evidence of pagophagy indicates it is younger than geophagy, it too is centuries old. The oldest written description was authored by a French Royal physician in the seventeenth century (Riverius et al. 1663). In his concisely named oeuvre “The practice of physick wherein is plainly set forth the nature, cause, differences, and several sorts of signs: Together with the cure of all diseases in the body of man. With many additions in several places never printed before,” Riverius described the desiderata of those with pica:

"Some require sowr things, sharp, bitter, and very cold, so that they are delighted with the continual use of unripe Fruits, Vinegar, Snow, Juyce of Lemmons, Pomegranates, and Oranges, cold Water, Snow, Ice and the like. Others desire Earthy, Dry, and burnt things, as Cloves, Cinnamon, Nutmegs, and other Spices, Salt-Ashes, Chalk, and the like.” (Bk. 9, ch. 3)"

Pagophagists are as picky about their ice as geophagists are about their earth. Once a person finds exactly the ice they like, they are hooked, returning to the restaurant or party store or laboratory icemaker again and again, sometimes multiple times per day. On, a Web site dedicated to the joys and difficulties of chewing lots of ice, the general consensus is that the ice at Sonic fast-food drive-ins is superior:

"Hi I am visiting this site for the first time as I sit here at work doing what I am notorious for . . . chewing ice. This is the first post I saw and I am cracking up! Sonic has the best ice on earth aside from what I call rabbit turd ice. I know that sounds gross but I am guessing if you love to chew ice like I do you know what I mean . . . you know that ice that is soft and almost cylindrical in shape. Well anyhoo glad I found this site. Hopeful knowing there are others out there like myself I won’t feel so strange about it. :lol:"

"OHHHHH, dat Sonic Ice goes so hard!!! I love Sonic Ice, LOL, I thought I was the only one but I buy it by the bags not cups!!! It costs $2.12."

In fact, there are so many fans of Sonic Ice that it even has its own Facebook page, with 162,063 fans. One quote on Sonic Ice’s wall: “I NEVER join these things but I really DO love Sonic Ice!!”

The lengths people go to, especially pregnant women, to obtain the ice they crave can be astounding. They drive for hours or sleep very little so that they can crunch their ice away from the prying eyes of their family. One woman even bought the machine they use at Sonic (a Scotsman MDT2C12 Touchfree Air Cooled Cubelet Ice Maker/Dispenser) to have in her home: “Found on e-bay, paid $2250 for the thing.” Short of purchasing an industrial icemaker, there are other tactics to ensure a steady ice or frost supply: frequently borrowing trays of ice cubes from many neighbors; leaving the door of a deep freezer open a crack so that frost continuously forms; and sending boyfriends and husbands out for ice, even in snowstorms (Cooksey 1995).

“A devouring passion”

You may have noticed that one common feature among these picas is strong cravings. To say that geophagists “eat earth” does not convey the frequently imperative nature of their drive. In fact, the desire for pica substances is so strong that those who have not experienced pica have long equated the strength of these cravings with those for tobacco, alcohol, and drugs.

In Jamaica in 1788 : “Their attachment [to earth] is greater than even that of dram drinkers to their pernicious liquor” (Hunter 1788:310).

In Georgia in 1840 : “From the oldest to little children, [they] are as much addicted to the eating of clay as some communities are to the use of tobacco and snuff” (Burke 1978 [1871]:79).

In England in 1842 : “Powerfully do the morbid appetites enslave a large portion of mankind—from the opium of China to the tobacco of Virginia, and from the beer of England and the whisky of Ireland to the clay of Carolina” (Buckingham 1842:551).

In India in 1906 : “The uncontrollable craving for this [earth] is like the opium or alcohol habit, and the ravenous symptoms and anxiety in the faces and actions of the eaters are similar to those found in the devotees of one or other of these vices” (Hooper and Mann 1906:264).

Those who actually engage in pica use similarly strong terms to characterize their cravings; sometimes the language used to discuss pica is exactly that used to describe illicit drug use. For example, one of the Swahili terms used in Pemba to discuss pica is vileo , which is the same word used to describe addiction to cigarettes, alcohol, or hard drugs. A Washington, D.C., woman told a reporter for Time magazine that, “When I’m pregnant, it’s just like taking dope” (1967). And such language is echoed in the Yahoo! Cornstarch Discussion Group:

I had been 2 days clean and went over to a friends house. I had told this friend that I did cornstarch and was getting off it. They wanted me to finish this box, it only had a little in it, just to see how I do this. [. . .] I finished off the starch (it wasn’t much) and have been craving that taste ever since!!!! I even drove miles out of my way to go to this store they were talking about. It wasn’t there. MAN I WANT THAT TASTE AGAIN!!!!

Given this strong desire, it should be no surprise that people have a very hard time ceasing their pica behavior. Pica literature is peppered with phrases like “nothing is sufficient to prevent them from indulging their morbid cravings” (Imray 1843). Descriptions of the punishment meted out to slaves who engaged in pica make it clear that even terrible physical punishment, including whippings and iron masks, was no deterrent (cf. chapter 6).

Difficulties with stopping are also a feature of 21st-century pica behavior. In Laos, threats of arrest did not cause the cessation of geophagy (Rowles-Sewing 1981). Women in the Yahoo! Cornstarch Discussion Group spend a lot of time sharing advice on techniques for curbing behavior; promises to God, extraordinary weight gain, and threats of divorce are frequently insufficient to dissuade them. Pica today remains the “devouring passion” it was described as a century ago (Galt 1872). For this reason, the phrase “craving and purposive consumption” is an important part of the definition of pica.

Who Does Pica?

We know that people around the world engage in pica; at this very moment there are hundreds of thousands of people experiencing cravings to eat all kinds of non-food items. But there are some segments of the population more likely to engage in pica than others. Pregnant women easily comprise the largest proportion of consumers, while children form the second largest group. (Detailed discussions of populations more likely to engage in pica are found in chapters 6, 8, and 9.)

Pregnant Women

Pica is so overwhelmingly associated with pregnancy that in some places it is synonymous with pregnancy. For example, when a senior government physician in Malawi was asked if village women ate clay in pregnancy, she smiled: “It would be very surprising if pregnant women in Malawi did not eat clay. That’s how you know when you are pregnant!” (Hunter 1993:75). In Nigeria, “the association of this custom with pregnancy reaches the point that women note axiomatically that if a woman is observed to eat clay, she must be pregnant” (Vermeer 1966:200).

This association with pregnancy is both ubiquitous and very old. Hippocrates (460–377 BCE.) is responsible for the first written record of geophagy, and in it he specifically identifies pregnant women. “If a pregnant woman would like to eat earth or charcoal, and then eats it, the child that enters this world will be marked on its head from these substances” (Hippocrates 1853:487).

One of the most luscious passages about pica during pregnancy is found in the Raghuvams h a , a thirteenth-century epic Indian poem that traces the genealogy of dynasty of warrior kings (Kale 1997; see also Appendix D for more pica references in literature). Queen Sudakshina became a geophagist during her pregnancy; she had “set her heart upon clay in preference to all other objects of taste” (Canto III, nos. 3 & 4). Although the king didn’t like the smell of “her mouth, fragrant with clay,” his aversion to her earthy breath was overshadowed by her alluring pregnant body. “As days rolled on, her two breasts, growing exceedingly plump, and with nipples black all round, far surpassed the loveliness of a couple of well-formed lotus buds with black bees perched upon them” (Canto III, no. 8).

There is also plenty of scientific evidence that pica is associated with pregnancy. Biomedical studies of the prevalence of pica in dozens of antenatal populations in North America, South America, Africa, and Europe have shown again and again that pregnant women regularly engage in pica.


Young children are the second most likely to purposively consume non-food substances, although there are far fewer anecdotal reports of their pica behavior than for pregnant women (Young 2010). Please note, pica among children does not include exploratory mouthing behaviors. To be considered pica, children must actively seek out clay, paper, chalk, dirt, termite hills, etc. For this reason, pica cannot possibly occur until after children are over two years of age. There are also far fewer clinic-based studies of the prevalence of pica among schoolchildren, but the few that have been conducted suggest ranges from 1.7% (among children in upstate New York) (Marchi and Cohen 1990) to 74.4% (among Zambian schoolchildren) (Nchito et al. 2004). All epidemiologic studies on the prevalence of pica in children are presented in Appendix C.


Although this book is about human behavior, geophagy in the animal kingdom is widespread enough to merit mention. It is important to know that non-food consumption is not only a human activity because it suggests that there is some benefit to the phenomenon among us human animals. Wild animals almost always behave in ways that are likely to promote their survival.

The below-referenced instances of geophagy among animals do not include visits to salt deposits or the practice of licking the earth in areas with high salt concentrations. In such instances, the motive is clear: the animal is seeking sodium. By geophagy, I am referring to animals who actively seek out the earth itself, in the absence of sodium. And many, many species do this.

There are some wonderful review articles about geophagy in nonhuman primates (Krishnamani and Mahaney 2000), terrestrial mammals (Hui 2004; Klaus and Schmid 1998), herbivores (Kreulen 1985), and birds (Diamond et al. 1999). And there are an even greater number of scientific articles detailing observations among individual species. For example, along the border between Kenya and Uganda, elephants have excavated deep caves in their quest for earth (Houston et al. 2001; Lundberg et al. 2006). In Yellowstone, grizzly bears consume soil in early spring and late summer (Mattson et al. 1999). Smaller mammals do, too, including hindgut herbivores like rhinoceros, zebra, and horse; ruminants like giraffe, kudu, eland, antelope, water buffalo, and duiker; and small herbivores like tapir, grouse, rabbit, squirrel, koala, and tortoise (Barlow 2000).

But Why?

By now, you must be wondering why all these human and nonhuman animals are eating earth and starch and ice, given the hassle, the cost, and the pleas not to. That is the exact question I propose to answer in this book. It’s a tough one; after all, scientists continue to debate its function, if any, after two thousand years of study. But given how widespread the practice is, especially among some of the most vulnerable segments of our society (pregnant women and children), it’s one worth answering.

In the pursuit of an answer, we will scoot through the history of medicine, touch on some of the world’s greatest literature, and enter the guts and minds of pregnant women, encountering armchair anthropologists, Nobel laureates, and tortured slaves along the way. We will unravel royal intrigues, become acquainted with several pantheons, and test a number of scientific hypotheses using a range of data, from randomized clinical trials to mineralogical analyses. But best of all, through the concurrent study of culture and biology, we will make scientific progress by making sense of some very chaotic data.

To begin, I will outline the biocultural framework, the perspective I have used to study pica (chapter 2). You may want to skim it if you are reading only for content about pica, but it does introduce some useful concepts that are peppered throughout the rest of the book. The rest of part I (chapters 3–5) further contextualizes pica by dealing broadly with humans’ use of non-food substances. In chapter 3 (“Medicine You Can Walk On: The Amazing Properties of Clays”), I describe the many ways that pica substances have been used both internally and topically to heal a range of ailments from the “bitings of venemous poison-outcasting beasts” to explosive diarrhea. Chapter 4 (“Religious Geophagy: Sacredness You Can Swallow”) details the uses of earth in religion: Christianity, Islam, Hinduism, and hoodoo folk magic. Both chapters 3 and 4 deal with geophagy that is not pica; these are not instances of craving earth, but provide an important context for the practices of pica. Chapter 5 (“Poisons and Pathogens”) presents the darker side of pica and describes the harm that pica substances have been associated with. With this background, you will have the knowledge necessary for the second part of the book, which evaluates the many explanations of pica.

Part II deals uniquely with the etiology, or causes, of pica and opens with chapter 6 (“Dismissal and Damnation”), about the historical perspectives on the causes of pica among six groups who have most frequently been documented as engaging in pica. For each group, I suggest why such conclusions can be rejected.

Chapters 7, 8, and 9 are the most data-rich, scientific chapters of the book. They describe and evaluate the three most plausible hypotheses about the physiological functions of pica: that it is a response to hunger; that it is a response to a micronutrient deficiency such as iron or calcium; and that it occurs to protect against harm from toxins and pathogens. By chapter 10 (“Putting the Pica Pieces Together”), you’ll be very knowledgeable about pica.

As you read, you may want to refer to the glossary and appendices at the end of the book. Four of the appendices summarize different types of biomedical studies on pica. Additionally, there are two more that attempt to organize different types of information on pica: a timeline of notable moments in the history of pica and instances of pica in literature.

One proviso: this is not an arcane volume that requires intimate knowledge of nutritional, soil, or biomedical sciences. After several years of studying pica, I find it too fascinating a topic to address only in academic journals. Thus, I have sought to write a book that is both accessible and pleasurable for people with a variety of backgrounds. In fact, you don’t even need to have heard of pica to enjoy this book. I’ve worked hard to distill and translate the jargon from thousands of sources so that the only prerequisite to reading this book is a healthy dose of curiosity. Of course, if you would like greater scientific detail than I provide here, I would encourage you to track down some of the hundreds of references with which this book is laced. Finally, those who have specific questions about pica or want to share their own personal experiences can contact me at


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About the Author

Sera L. Young is a faculty member of the Division of Nutritional Sciences at Cornell University in Ithaca, New York.

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