New York City ? Researchers have solved a medical mystery that has eluded them for hundreds of years, demonstrating that an abundance of abnormal skin proteins causes the blotchy skin condition called rosacea.

In a study published Sunday in the online edition of the journal Nature Medicine, scientists showed that people with rosacea have too much of a protein called cathelicidin that is processed incorrectly.

The results could aid researchers in designing an effective treatment for the disease, which affects 14 million people in the United States.

Rosacea is a skin disease that causes redness, visible blood vessels, bumps and pimples on the face. It tends to strike more women, usually between ages 30 and 60, but men often have more severe symptoms.