Liz Agar is a sporty, attractive 26-year old. But she is overwhelmed by an obsession that dominates her every waking moment.
She has an overpowering need to pull out her hair. The urge is so compelling and regular that a large area of her head is now completely bald.
Liz has trichotillomania, a disorder characterised by compulsive hair pulling followed by a brief sense of gratification or relief. The condition is surprisingly common, affecting two in every hundred people.
When she pulls out a hair with a large follicle, she likes to bite into the end of the hair. This gives Liz a fleeting but intense sense of relief. She also pulls out her eyelashes and rubs them against her face.
"But the thing is, it [trichotillomania] is not taking the anxiety away, because you're just stressing yourself more by destroying yourself," says Liz.
Liz has lost lots of her hair because of her habit
She has had the condition since she was twelve, and the outward signs of her behaviour cause her lots of embarrassment.
Mangy animal or normal?
"Sometimes I think I'm like a mangy animal and then sometimes I think I'm fine. I know I'm a normal person, but deep at the back of my mind I almost feel retarded, and it's a feeling I've got from other people too," says Liz.
Because the bald patch is at the back of Liz's head, she used to cover it up by wearing her hair up. But now Liz is having a special hairpiece made. The hairpiece has a dual purpose - it will cover up Liz's bald patch, but it is also hoped that it will stop her from picking at her hairs.
After a few months, it is clear that the hairpiece has been a success. Liz's hair is starting to grow back.
Liz bites into a hair follicle
Liz says her behaviour is a direct result of a senseless urge to pull her hair, not the sensation of pulling it, which defines her as having an OC spectrum disorder. People with OC spectrum disorders carry out their behaviour because they are unable to resist it, not because they are seeking pleasure from it.
Scientists in the United States have recently made a breakthrough in the understanding of this disorder by knocking out a gene called Hoxb8 in laboratory mice.
These mice are normal in most respects, but they over-groom themselves, ending up bald and covered with sores. It is thought that this gene could provide the basis for disorders like trichotillomania in humans.