Some sunscreen lotions intended to protect the skin may actually irritate it because they contain a chemical that can cauuse allergic reactions upon exposure to sunlight, a dermatologist says.

Dr. Elizabeth Knobler, a research fellow at New York University, studied four patients who developed rashes after using high-protection lotions to block out the sun's harmful ultraviolet rays.

Knobler's tests showed the patients were suffering from light-induced allergic reactions caused by the chemical benzophenone in their sunscreens.

The findings prompted Knobler to recommend allergy-prone people carefully read the ingedient labels on sunscreens. In a recent presentation at the American Academy of Dermatology's annual meeting, she also urged doctors to include benzophenone in their patch tests of people who suffer allergic skin reactions.

Knobler did not identify the benzophenone-containing sunscreens, noting the formulations of such products often change from year to year although the trade name remains the same.