The exact etiology of pica remains unknown despite the fact that pica has been reported since antiquity. Pica is considered a multifactorial phenomenon because of this potential for multiple etiologies.1,4 Several theoretical approaches attempt to explain pica from nutritional, sensory, neuropsychiatric, ethnic, or psychosocial perspectives.4,6,13
The most common nutritional theories attribute pica to deficiencies of specific minerals including iron and zinc. Several case studies describe patients with low iron or zinc levels whose pica behavior diminishes with iron or zinc supplementation.4 Clay, especially red clay from the southern United States, is high in iron and may prompt pica behavior in an attempt to supplement for this micronutrient.16 However, clay eating may be the cause of iron deficiency anemia, as clay is an iron chelator and binds iron, reducing its bioavailability. A less common theory postulates that people eat nonfood substances because they do not have anything else to eat.16
Sensory theories focus on the reports that patients say they enjoy the taste, texture or smell of the item they are consuming.13 The “crunch” of cornstarch or clay, the “chew” of rubber bands or the smell of foam rubber are described as pleasing to the consumer.
A neuropsychiatric component is supported by evidence in laboratory animals with certain brain lesions and abnormal eating behaviors in these animals. Therefore, pica may be associated with certain brain disorders in humans.13 Recent evidence indicates that pica may be part of the obsessive-compulsive disorder (OCD) spectrum of diseases. There are case reports from five patients undergoing OCD treatment who indicate their pica behavior is a ritualistic behavior they are compelled to carry out and that eating the substance lessens the anxiety or tension they experienced.13 Traditional OCD therapy, which is primarily psychotherapy, had a variable effect on the pica behavior in these patients. These case reports lend support to the theory that, at least in some patients, pica may be a manifestation of OCD.13 Pica has comorbid associations with other diseases and disorders including autism, autism spectrum disorders (ASD), psychosis, and developmental disabilities.2,7,11,13 Neurochemical and neuropathological changes that occur in patients with dementia may also contribute to a change in eating habits resulting in pica behavior.4
Pica is a widespread practice in India and has been reported in Australia, Canada, Israel, Iran, Uganda, Wales and Jamaica.6 Pica is culturally acceptable among families of African heritage and is reported to be problematic in 70% of provinces in Turkey. In Guatemala, clay is molded into small religious icons, called panito del senor, and consumed. Pica has been associated with fertility rites; the eating of soil is thought to ensure future offspring. Clay and starch have been eaten by pregnant women to ease morning sickness.4 Some clay contains kaolin, formerly the active ingredient in Maalox® and Kaopectate. These over-the-counter products are used to treat nausea, diarrhea and vomiting.16 Clay is also consumed to coat the stomach and intestines before eating foods such as fish that may contain toxins or pathogens.4,16 This coating could slow the absorption of these toxins and pathogens.16 It is understandable that children could mimic the pica behavior of those around them as a practice as well as a method of relieving intestinal distress.4
Psychosocial theories of the etiology of pica suggest an association with family stress (abuse, parental separation, neglect or poor parenting), a smaller social support network and as a display of aggression.4,13