The person must regularly eat these craved substances for a month or more before a diagnosis is given. Perhaps ten to twenty percent of children have pica at some time before adulthood. Depending on the population, zero percent to sixty-eight percent of pregnant women have pica. Those in lower socioeconomic groups seem to have more problems with these cravings. In some cases, pica is related not to dietary deficiencies but to folk traditions passed on in families or ethnic groups.
Some people treat clay or dirt eating as a part of daily routine, somewhat like smoking.
Others believe that eating dirt will help them incorporate magical spirits from the Earth into their bodies. Still others believe that certain kinds of clay will suppress morning sickness when eaten. Some children with pica may be imitating a pet dog or cat. Stress may be a precipitating factor, especially the stress of dieting when the person tries to relieve hunger and cravings with non-food substances. There is evidence to support the hypothesis that at least some pica is a response to dietary deficiency.