Updated: Mar 1, 2021
UVB rays were once thought to be the culprits because they penetrate and affect the epidermis, but UVA rays are now known to be equally, if not more damaging. According to Dr. Madhu A. Pathak at the Harvard Medical School, “Many lines of evidence indicate that the primary biological actions of UVA radiation involve DNA damage”. UVB emissions from the sun undergo significant seasonal variations; the UVA emissions, however, do not appreciably change over the course of the year. The amount of solar UVA reaching the earth's surface is much greater than that of UVB. Also, UVA penetrates most window glass and many plastics that do not transmit UVB. Always check to make sure your sunscreen protects from UVB and UVA, but be aware that regardless of the advertising no sunscreen product screens out all UV rays. The best defense is to try to minimize your exposure between the hours of 10 a.m. and 4 p.m. The effects of infrared rays (felt by the body as heat) are not fully known, but according to Drs. Lorraine and Albert Kligman from the University of Pennsylvania, “They cannot be ignored in connection with photoaging”.