Until recently, the DSM treated pathological grooming a bit like an afterthought and put it in a catch-all category called “not otherwise classified.” But the new DSM proposes to lump together pathological groomers and those with mental disorders like OCD. That includes people who wash their hands compulsively or have to line up their shoes a certain way.

These behaviors have a lot in common. In both cases, it’s taking a behavior that’s normal and healthy and putting it into overdrive, doing it to the point of being excessive. But in at least one way, OCD and pathological grooming are also very different.

“In OCD, the compulsion is really unwanted,” says Mathews. People with OCD don’t want to be washing their hands or checking the stove over and over again. There is no fun in it. There’s fear — fear that if they don’t do something, something else that’s very bad will happen to them.

But from her pathological grooming patients, Mathews hears a very different story: They enjoy it. “It’s rewarding. It feels good. When you get the right nail, it feels good. It’s kind of a funny sense of reward, but it’s a reward,” she says.