People eat dirt for reasons that range from deep cultural tradition to nutrient deficiency to unexplained cravings during pregnancy. The practice, called geophagy, has been documented on every inhabited continent and stretches back thousands of years. It is not simply a bizarre habit. For many communities, it is a normal part of life, and for researchers, it remains a surprisingly complex puzzle.
A Practice With Deep Cultural Roots
Eating specific types of clay or soil is a longstanding tradition in parts of sub-Saharan Africa, South America, and the American South. The Aymara people of Bolivia and Peru have practiced geophagy for generations. In rural Holmes County, Mississippi, researchers documented 25 separate sites where Black communities sourced clay for eating, most of them tied to established rural settlements throughout the county’s upland areas. The clays are not scooped randomly from the surface. They are carefully extracted from deeper soil layers, selected for texture and taste.
Historical records also describe soil eating among Texas Coastal Indians in the early sixteenth century and among poor white communities in the South, where the practice was common enough to produce the term “clay eater.” In West Africa, edible clay is processed into products sold in markets under names like Calabash Chalk, Nzu, Poto, and Calabar Stone. These are often shaped into pellets or chunks that look like balls of dried mud and are widely available in African grocery stores across Europe and the United States.
In communities where geophagy is traditional, it carries no stigma. People describe specific preferences for the taste, texture, and smell of particular clays, much the way someone might prefer a certain mineral water. This cultural dimension is important because it means not every case of dirt eating signals a medical problem.
The Nutrient Deficiency Connection
One of the most common explanations is that the body craves soil to correct a mineral deficiency, particularly iron or zinc. The logic sounds intuitive: soil is rich in minerals, so a depleted body reaches for it. But the science tells a more complicated story.
When researchers simulated what happens to soil as it passes through the human digestive system, the results were striking. The soils tested retained about 90% of the iron already present in the digestive solution, with individual soils absorbing between 87% and 95%. For zinc, the result was even more dramatic: no detectable zinc remained in the solution after the soil passed through the simulated intestine. Copper was similarly wiped out, with a 100% negative balance. In other words, eating soil does not deliver these critical minerals. It actively strips them from whatever else you have eaten.
This means geophagy can actually cause or worsen the very deficiencies people assume it corrects. Clay’s ability to exchange charged particles lets it bind tightly to iron and zinc in the gut, blocking their absorption. So a person who is mildly iron-deficient and begins eating clay may become significantly more deficient over time, creating a self-reinforcing cycle: the deficiency triggers the craving, and the craving deepens the deficiency.
There is one partial exception. Some soils can release calcium, magnesium, and manganese in amounts the body can absorb. But this depends heavily on the type of soil. Calcareous soils (those naturally rich in calcium-bearing minerals) may offer some supplementation, while other soils release none of these nutrients at all.
Why Pregnant Women Crave Soil
Pregnancy is the single most common context for geophagy worldwide. Prevalence varies enormously depending on the population studied, from as low as 0.004% among pregnant women in Denmark to as high as 92.5% among pregnant and lactating women in one Nigerian study. Race and cultural background are major factors. Research has found a four-fold increase in pica during pregnancy among African American women compared to white women in the same studies.
The leading theory for years was that pregnancy-related anemia drives the craving. Pregnant women need substantially more iron, and many become deficient, so the thinking was that the body instinctively seeks out mineral-rich soil. But the data complicates this idea. More people with anemia do not engage in pica than do, which means anemia alone is not a sufficient explanation. Researchers now believe cultural factors play a large role, with the practice being passed between generations in communities where it is considered a normal response to pregnancy nausea or a traditional remedy for morning sickness. The craving may then contribute to worsening anemia rather than relieving it.
When Dirt Eating Becomes a Medical Concern
In clinical terms, eating non-food substances falls under a condition called pica. To meet the diagnostic threshold, the behavior needs to persist for at least one month and occur outside a cultural context where it is considered normal. This distinction matters. A pregnant woman in rural Nigeria eating clay from a traditional source is engaging in a cultural practice. A child in a U.S. suburb compulsively eating playground dirt may have a diagnosable condition.
Pica can appear in young children (who frequently mouth non-food objects as part of normal development), in people with intellectual disabilities, and in anyone with severe nutritional deficiencies. It is also associated with obsessive-compulsive spectrum disorders. The key clinical question is always whether the behavior is culturally embedded, developmentally expected, or a sign of something else going on.
Real Health Risks of Eating Soil
Regardless of the reason someone eats dirt, the health risks are real. An analysis of 88 geophagic soil samples purchased in Central, West, and East Africa, as well as in Europe and the United States, found measurable contamination with bacteria and heavy metals. Lead concentrations reached up to 148 mg/kg, with a median of 40 mg/kg. Mercury levels went as high as 0.64 mg/kg, and cadmium reached 0.57 mg/kg. Lead, mercury, and cadmium are persistent toxins that primarily damage the kidneys and brain, and exposure during pregnancy or early childhood can impair a child’s brain development and kidney function.
Interestingly, no parasitic worm eggs were found in the commercial samples tested, which suggests that processed and packaged clays may carry lower parasite risk than soil eaten directly from the ground. But heavy metal contamination remains a concern regardless of the source.
Calabash Chalk, one of the most popular commercial products, has been specifically flagged by New York City’s health department for containing both lead and arsenic. The city issued a direct warning to stop using these products, noting that lead poisoning during pregnancy can cause complications and learning and behavior problems in young children, while long-term arsenic exposure raises the risk of cancer, skin lesions, and nervous system damage.
The Paradox at the Center of Geophagy
The most puzzling thing about eating dirt is that it does not do what most people assume it does. Soil is mineral-rich, but those minerals are largely locked up in forms the human body cannot access. Worse, certain clays actively pull essential nutrients like iron, zinc, and copper out of the digestive tract before they can be absorbed. Some researchers have proposed that this binding capacity might actually be the point: clay could act as a natural detoxifier, binding to harmful substances in food (plant toxins, pathogens) and carrying them safely through the gut. This “detoxification hypothesis” would explain why geophagy is most common in pregnancy, when the body is especially vulnerable to foodborne illness and toxins.
Other researchers point to the simple sensory experience. Many people who eat clay describe craving the smell after rain, the gritty texture, or the cool earthy taste. These sensory qualities may trigger reward pathways in the brain that have nothing to do with nutrition and everything to do with comfort and familiarity, especially when the practice is learned in childhood from a mother or grandmother.
No single explanation accounts for all cases. Geophagy sits at the intersection of biology, culture, psychology, and ecology, which is exactly why it has fascinated scientists for centuries and why a simple “they need minerals” answer falls short.