NEW YORK, Nov 23 (Reuters Health) - Women who rely on their foundation makeup to shield their faces from the sun may need to touch-up every couple of hours. A study of "foundation migration" shows that the makeup tends to collect in facial lines not long after a woman smoothes it on, leaving most of her face exposed to the sun's damaging rays.

"Foundations with an SPF (sun protection factor) provide a benefit to consumers," the study's author, Dr. Zoe Diana Draelos, said in a statement. "However, it is important for consumers to be aware that if they are going to be outside for an extended period, they can only rely on their foundation to protect them from the sun for approximately 2 hours."

Draelos came to that conclusion after studying 12 women who wore various types of foundation for 8 hours in an indoor, controlled environment. Using a video microscope, she charted the makeup's movements over the women's faces throughout the day.

It turned out that the foundation--be it liquid, cream/powder or lotion--found its way into the fine lines of the women's faces and tended to gather around hair follicles. The migration happened more quickly for women with oily skin, and the cream/powder formulation appeared most prone to shifting.

Draelos, of Wake Forest University School of Medicine in Winston-Salem, North Carolina, reported the findings in a recent issue of the Journal of the American Academy of Dermatology.

For women with oily skin, Draelos found, it took 2 hours or less for the foundations to lose their sun-shielding capability. The same was true for all the women by 4 hours after application.

This "degradation," Draelos notes, probably happens even faster in the real world where sweat, natural oil production in the skin and accidental removal of makeup would factor in.

Besides the fact that foundation migration might eliminate some women's sun shield, the makeup's tendency to pool around hair follicles might explain why some users show skin break-out near the hairline.

"This may explain why facial foundations that claim to be noncomedogenic and nonacnegenic cause (acne) eruptions in persons with self-diagnosed sensitive skin," Draelos writes.

This idea, she adds, remains only a hypothesis.

SOURCE: Journal of the American Academy of Dermatology 2001;45:542-543.

From Reutershealth.com