There are no reports of allergy to clay in the available scientific literature. However, in theory, allergy/hypersensitivity to clay, clay products, or constituents of clay may occur.
Side Effects and Warnings
The practice of eating dirt, clay, or other non-nutritious substances is called "pica" or "geophagia," and may occur in early childhood or in mentally handicapped people. Clay or dirt eating has been associated with lead poisoning in infants, children, and pregnant women, with potential risks such as low red blood cell count and brain damage. Death has occurred, related to complications of lead poisoning and brain damage after drinking from a glazed clay pitcher. Clay pots containing candy have been recalled in the United States by the Food and Drug Administration due to high levels of lead in the candy, absorbed from clay pots. Pica may carry a risk of central nervous system damage. The risk of neurolathyrism, a neurodegenerative, irreversible disorder that causes spastic paraparesis of the body leading to paralysis, was reported to quadruple in a case-control study in Ethiopia when cooking grass pea with clay utensils.
Clay products may contain varying amounts of contaminants including aluminum, arsenic, barium, nickel, and titanium. Elevated levels of 2,3,7,8-tetracholorodibenzo-p-dioxin have been found in fish and eggs from chickens fed a diet including clay. Chronic clay eating has also been associated with imbalances of blood chemistry, such as increased calcium or magnesium, decreased iron and potassium. Myopathy due to severe hypokalemia (low blood potassium levels) has been reported in one case report with large quantities of clay ingestion.
In the 19th Century, a condition was described called "Cachexia Africana," including a swollen appearance, enlarged heart, increased urination, and death. Descriptions of people who chronically ate clay in the 19th Century noted skin that was initially dry and shiny, and in late stages of disease, especially in children, skin ulcerations occurred over the arms and legs. Chronic clay eating has also been associated with small gonads (testes), and muscle injury.
Heartburn, gas, loss of appetite, constipation, diarrhea and vomiting after meals have been reported with use of clay. One study on safety using NovaSil clay for two weeks found that mild gastrointestinal effects occurred such as abdominal pain, bloating, constipation, diarrhea and flatulence, but that these effects were no more common than placebo. Clay eating has also been associated with intestinal blockage and injury, bowel rupture (perforation), formation of stones in the intestine, and enlarged liver/spleen.
It is reported that children with pica are more likely to develop lung infections. Chronic bronchitis, trouble breathing, and infections have been associated with dust exposure in the heavy clay industry. Hookworm infections may result from eating clay. Tetanus contracted from clay has been described in an infant who ate clay, and in a newborn whose umbilical cord was wrapped in clay.
One study on safety using NovaSil clay for two weeks found that mild gastrointestinal effects occurred such as abdominal pain, bloating, constipation, diarrhea and flatulence, but that these effects were no more common than placebo.
Pregnancy and Breastfeeding
Use of clay during pregnancy or breastfeeding is not recommended. Eating clay during pregnancy may increase the risk of toxemia or complications at birth.
Adults (18 years and older)
There is not enough scientific evidence to recommend safe use of clay.
Children (younger than 18 years)
There is not enough scientific evidence to recommend safe use of clay in children.
Interactions with Drugs
When taken together, clay may inhibit the absorption of drugs such as cimetidine (Tagamet®).
Kaolin has been shown to reduce the bioavailability of quinine in laboratory study.
Interactions with Herbs and Dietary Supplements
Clay can interfere with iron absorption.