Trichotillomania (TTM, also known as trichotillosis, or more commonly as trich) is defined as "hair loss from a patients repetitive self-pulling of hair" and is characterized by the repeated urge to pull out scalp hair, eyelashes, facial hair, nose hair, pubic hair, eyebrows or other body hair, sometimes resulting in noticeable bald patches. Trichotillomania is classified in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) as an impulse control disorder, but there are questions about how it should be classified. It may seem, at times, to resemble a habit (Habit (psychology)), an addiction, a tic disorder or an obsessive-compulsive disorder.

The disorder "leads to noticeable hair loss, distress, and social or functional impairment", and is "often chronic and difficult to treat".

Trichotillomania may be present in infants, but the peak age of onset is 9 to 13. Depression or stress can trigger the trich. Due to social implications the disorder is often unreported and it is difficult to predict accurately prevalence of trichotillomania; the lifetime prevalence of trich is estimated to be between 0.6% (overall) and 1.5% (in males) to 3.4% (in females).

The name, coined by French dermatologist Fran�ois Henri Hallopeau, derives from the Greek: trich- (hair), till(en) (to pull), and mania ("an abnormal love for a specific object, place, or action").