Dr. Holick explains what the SPF numbers on sunscreen stand for.
An SPF of 10, for example, means that you could stay out 10 times longer before you would get a sunburn. So say if you were to get a sunburn in June at noon time on Cape Cod after 15 minutes, then for SPF of 10, you could theoretically stay on for 150 minutes.
SPF of 15 will absorb about 95% of the ultraviolet B radiation that’s responsible for causing sunburn. So as a result, not only will it reduce your risk of having a sunburn, but it will also reduce your ability to make vitamin D in your skin.
About Dr. Michael Holick, Ph.D., M.D.:
Michael Holick, Ph.D., M.D., is the Professor of Medicine of Physiology and Biophysics at Boston University School of Medicine. He received his medical degree from the University of Wisconsin, Madison and performed his residency and fellowship at Massachusetts General Hospital. Dr. Holick specializes in vitamin D, calcium, bone metabolism, photobiology of vitamin, and osteoporosis. Dr. Holick is also the recipient of the American Skin Associations Psoriasis Research Achievement Award, the American College of Nutrition Award, the Robert H. Herman Memorial Award in Clinical Nutrition from the American Society for Clinical Nutrition, and more.