Indeed it is, and did you put some on yet today? Derek Cripps is the dermatologist whose research helped lead to the SPF — sun protection factor — ratings scale. After his residency at the University of Michigan, he joined the UW’s Department of Dermatology in the UW Medical School (today’s School of Medicine and Public Health) as a professor in 1965. In the early ’70s, Cripps began to study why some sunscreens were more protective than others, and it was his 1974 NIH study that led to the development of the SPF scale — and its adoption by the Food and Drug Administration (FDA) as a standard. According to the FDA, SPF measures how much ultraviolet radiation, or solar energy, it takes for protected skin to sunburn relative to how much solar energy it takes for unprotected skin to sunburn. Contrary to popular belief, SPF isn’t related to the amount of time you spend in the sun. UW Health has some additional information and tips about sunscreen (yes, it does expire!), but here’s the short story: wear it!