Sun exposure appears to trigger a substance in the body that may lead to the visible blood vessels that often appear with rosacea, according to research funded by the National Rosacea Society and reported at the annual meeting of the Society for Investigative Dermatology.

"Our initial study showed that sunlight may indeed have a role in causing rosacea," said Dr. Marita Kosmadaki, research fellow, Department of Dermatology, Boston University, who presented results of her research with Dr. Mina Yaar, professor of dermatology at Boston University.

Drs. Yaar and Kosmadaki found that exposure to ultraviolet (UV) radiation - a component of sunlight - led to the production of vascular endothelial growth factor (VEGF), a substance that has been linked to the development of visible blood vessels (telangiectasia).

"The melanin in the skin of darker-skinned individuals appears to make it difficult for UV radiation to reach the lower layers of the skin," Dr. Kosmadaki noted. "As a result, in darker-skinned individuals VEGF would tend to be induced only in the upper skin layers, and hence would not affect the blood vessels. In contrast, sufficient ultraviolet rays could induce VEGF synthesis in the deeper skin layers in fair-skinned individuals."

Because other researchers had found the production of VEGF can be triggered by another molecule called tumor necrosis factor (TNF), Drs. Yaar and Kosmadaki hypothesized that the UV radiation first induced the production of TNF, and its release in turn led to the synthesis of VEGF.

They then tested whether a hexapeptide, which binds TNF and cancels its effect, would block VEGF production and leave blood vessels unaffected. However, their research found that blocking this single pathway was ineffective in preventing the production of VEGF.

"Our findings have shed new light on the potential pathogenesis of this vascular component of rosacea," Dr. Kosmadaki said. "It appears that sun-induced VEGF may play a significant role in rosacea, and its production seems to involve factors other than TNF. This opens the way for further research that may lead to substantial improvements in treatment and prevention."

In a recent survey of 1,066 rosacea patients, 81 percent reported that sun exposure aggravated their condition. Rosacea patients affected by sunlight are advised to protect their skin year round by using sunscreen.