It''s hard to ignore a face filled with disgust, but people with an unsightly skin disorder seem to have a muted response to such facial expressions. This reduced sensitivity may serve to protect them from hurtful reactions.
Christopher Griffiths, a dermatologist at Manchester University, UK, and colleagues showed people with psoriasis – a non-infectious skin condition that produces reddening and lesions – a series of images of faces while scanning their brains.
Images of disgusted faces elicited less activation in the insular cortex, which processes feelings and observations of disgust, compared with a control group. Images of fearful faces produced normal levels of activation in the amygdala, which responds to fear, in both groups.
Volunteers with psoriasis were also less likely to identify disgust in faces that showed only subtle signs of the emotion, compared with controls.
People often react with disgust to psoriasis, even thought it is not infectious, says Griffiths. He reckons the brain adaptations in people with the disease "emerged to protect people that do not conform to facial norms".
The psychological burden of the disorder is always far worse than the physical pain, says Linda Papadopoulos, a psychodermatologist based in London who specialises in the social effects of skin disorders.
"This study is fascinating. It''s the first I know of that shows neurological changes in psoriasis sufferers, but the results don''t surprise me," she says. "People with obvious skin disorders often show behavioural changes."
Journal reference: Journal of Investigative Dermatology, DOI: 10.1038/jid.2009.152