What exactly happens when a person suffers from the mental disease tricotillomania?

Hair is pulled out: Trichotillomania is a mental illness in which people pull out their hair, resulting in noticeable hair loss. This could be hair of the head, eye brows, eye lashes, or anywhere. They experience a tension before pulling out the hair, and gratification, pleasure, or relief when pulling it out. The problem is quite distressing to them. It is treated as an impulse-control disorder.