A new study conducted by researchers at the University of California has found that it is not just one, but a combination of two abnormal factors, that cause adult acne or rosacea.

Adult acne is a common condition which affects fair-skinned people of mostly north-western European descent. It begins as erythema (flushing and redness) on the central face and across the cheeks, nose, or forehead but can also less commonly affect the neck and chest.

It is linked with a type of bacteria, and antibiotics are prescribed to treat its symptoms. It, however, worsens over time.

During the study, Richard L. Gallo and his colleagues first observed in the laboratory that small proteins of the body's host defence system called anti-microbial peptides caused the exact symptoms like redness, an increase in visible blood vessels, bumps or pimples, that rosacea did.

"When we then looked at patients with the disease, every one of them had far more peptides than normal." Nature magazine quoted Gallo as saying.

The researchers examined the source of these molecules to know why these patients had abnormal peptides.

The precursor form of these peptides, called cathelicidin, is known to guard the skin against infection. A deficiency of cathelicidin correlates with increased infection in other skin diseases.

The study found the opposite in rosacea patients, as excessive cathelicidin of a different form was present in their skin.