A low level of daily exposure to the sun’s ultraviolet A1 (UVA1) rays may cause skin damage at the molecular level after just a few days, according to research out of the University of Michigan Medical School in Ann Arbor.

The study, which is published online in JAMA Dermatology, highlights the need for better sunscreens that protect against UVA1. Currently, only zinc oxide and avobenzone are capable of blocking UVA1. Window glass, and most clothing, also don’t necessarily filter out all UVA1.

Researchers found that damage starts after just two daily exposures to a low amount of UVA1 light – which makes up most of the UV light we are exposed to throughout the day ( and tanning bed light, too). This damage increased with further daily exposures.

To arrive at their findings, researchers shined a low level of pure UVA1 rays, as might be encountered in daily life, on small areas of 22 volunteers’ buttocks. A day later, they measured changes in skin pigmentation. Then, they took tiny samples of skin, to detect which genes had been “turned on” by the light exposure. They repeated this process three more times on each participant.

After just two exposures, UVA1 rays caused skin cells to make molecules that break down collagen, the study showed. Moreover, the UVA1 also caused the skin to darken slightly with each exposure, but this tan didn’t protect against further production of matrix metalloproteinase 1 (MMP1), when the skin was exposed to more doses of UVA1. Statistical analysis showed the pattern of MMP1 production increased progressively with repeated exposure in the majority of patients.

UVA1-Induced Skin Cancer Link Possible

Though the current study didn’t assess the impact of UVA1 on genetic changes that can lead to skin cancers, other forms of UV are firmly linked to most types of cancerous skin lesions, the study authors note.