In individuals with autism, schizophrenia, and certain physical disorders (such as Kleine-Levin syndrome), nonnutritive substances may be eaten. In such instances, pica should not be noted as an additional diagnosis.

There is no single test that confirms pica. However, because pica can occur in people who have lower than normal nutrient levels and poor nutrition (malnutrition), the health care provider should test blood levels of iron and zinc.

Hemoglobin can also be checked to test for anemia. Lead levels should always be checked in children who may have eaten paint or objects covered in lead-paint dust. The health care provider should test for infection if the person has been eating contaminated soil or animal waste. The Diagnostic and Statistical Manual of Mental Disorders, 5th edition, posits four criteria that must be met for a person to be diagnosed with Pica:

Patients may be ashamed or actively attempt to disguise their symptoms. This can make diagnosis difficult as symptoms are not always immediately obvious, or have been deliberately hidden to avoid disclosure. If the patient admits to hair pulling, diagnosis is not difficult; if patients deny hair pulling, a differential diagnosis must be pursued. The differential diagnosis will include evaluation for alopecia areata, iron deficiency, hypothyroidism, tinea capitis, traction alopecia, alopecia mucinosa, thallium poisoning, and loose anagen syndrome. In trichotillomania, a hair pull test is negative.

A biopsy can be performed and may be helpful; it reveals traumatized hair follicles with perifollicular hemorrhage, fragmented hair in the dermis, empty follicles, and deformed hair shafts (trichomalacia). Multiple catagen hairs are typically seen. An alternative technique to biopsy, particularly for children, is to shave a part of the involved area and observe for regrowth of normal hairs.

Rapunzel syndrome, an extreme form of trichobezoar in which the "tail" of the hair ball extends into the intestines, can be fatal if misdiagnosed. In some cases, surgery may be required to remove the mass; a trichobezoar weighing was removed from the stomach of an 18-year-old woman with trichophagia.

Trichophagia () is the compulsive eating of hair associated with trichotillomania (hair pulling). In trichophagia, people with trichotillomania also ingest the hair that they pull; in extreme (and rare) cases this can lead to a hair ball (trichobezoar).

When it occurs in early childhood (before five years of age), the condition is typically self-limiting and intervention is not required. In adults, the onset of trichotillomania may be secondary to underlying psychiatric disturbances, and symptoms are generally more long-term.

Secondary infections may occur due to picking and scratching, but other complications are rare. Individuals with trichotillomania often find that support groups are helpful in living with and overcoming the disorder.

Excoriation disorder, and trichotillomania have been treated with inositol and N-acetylcysteine.

BFRBs are among the most poorly understood, misdiagnosed, and undertreated groups of disorders. BFRBs may affect at least 1 out of 20 people. Trichotillomania alone is believed to affect 10 million people in the United States.

Dermatophagia (from Ancient Greek "δέρμα" - skin - and "φαγεία" - eating) is a compulsion of gnawing or eating one's own skin, most commonly at the fingers. Sufferers typically bite the skin around the nails, leading to bleeding and discoloration over time. Some may consume the flesh during an episode.

Contemporary research suggests a link between impulse control disorders and obsessive–compulsive disorders, and this may be addressed in the "DSM-5", published in May 2013. Further information on OCD, other anxiety disorders, and dermatophagia and other impulse-control disorders can be found in the "DSM-IV TR".

Dermatophagia sufferers chew their skin out of compulsion, and can do so on a variety of places on their body. Sufferers typically chew the skin surrounding their fingernails and joints. They also chew on the inside of their mouth, cheeks, and/or lips, causing blisters in and outside of the mouth. If the behavior is left unchecked for an extended period, calluses may start to develop where most of the biting is done.

Skin chewing can be bolstered by times of apprehension and other unpleasant events. Blisters in particular can cause a feeling of desire to pull or bite off the affected skin (since the skin is dead, thus easily pulled off), which could be detrimental, causing infection. Another disorder, known as dermatillomania , the act of picking at one's skin, can sometimes accompany dermatophagia. People who suffer from dermatophagia can also be prone to infection as when they bite their fingers so frequently, they make themselves vulnerable to bacteria seeping in and causing infection. Dermatophagia can be considered a "sister" disorder to trichophagia, which involves compulsively biting and eating one's hair.