People with a disorder in which they are convinced they are ugly have a brain glitch when processing things they see, researchers say.

The findings, published in the journal Archives of General Psychiatry, shed light on body dysmorphic disorder (BDD), marked by a dramatically distorted self-image and obsessive thoughts about imagined or minor defects in their appearance.

University of California psychiatry professor Dr Jamie Feusner says an estimated 1 to 2 per cent of people around the world have BDD.

Some undergo repeated cosmetic surgery procedures in a futile attempts to fix the problems.

The cause of the disorder remains unknown, with experts suspecting that a variety of factors may contribute, from genetics to upbringing.

People with BDD often think of themselves as ugly or disfigured and may obsess about physical traits or minor and imagined flaws even when assured by others they look fine.

About a quarter of people with BDD attempt suicide.