Body dysmorphic disorder is a mental condition in which people consistently worry about perceived/imagined defects in their body when in fact there are none, or if there are they're very minor.
They often seek surgery to correct their imagined defects and they spend a lot of time obsessing over their looks, and try and cover up their perceived defects by using lots of make up and dressing to cover them.
Apparently people believe that it's closely related to OCD, but no one knows how it's caused or the brain chemistry behind it.
It usually develops in teenagers, probably as they see models in magazines and start to obsess over that as people with BDD often want to appear "perfect". I think one thing that can help or that's used as therapy is cognitive behavioural therapy, although I'm not too sure about that. They also used anti depressants to treat BDD at one point, but stopped as they found a link between anti depressants and feeling hopelessness and suicidal.
Now, they often use another type of anti depressants, but CBT is what's used more often than not.