It’s tempting to constantly reach for sunscreen that comes in a bottle or tube. However, you might be able to rely on a different type of sunscreen—a natural mechanism that develops as your skin is gradually exposed to the sun.
A telltale photo in a review published in Experimental Dermatology shows an arm that got sun exposure shortly after a cast was removed—red skin perfectly fills in where the cast previously wrapped around the lower thumb, across the middle of the back of the hand, and midway up the arm. The rest of the arm shows no sign of sun exposure.