Every sunscreen has a sun protection factor, or SPF, which is a measure of its strength or effectiveness. Each of us needs a different SPF, depending on whether, and to what degree, our skin burns or tans. A tan is the direct result of melanin, a brown pigment found in the epidermis that is produced when skin is exposed to sunlight.

Melanin protects the skin by absorbing, reflecting and scattering ultraviolet radiation before it penetrates the dermis, or underlying skin. However, armor that it is, melanin can’t prevent all the negative effects of the sun, and is often representative of damage. That’s why we need to use sunscreens. To determine what SPF your skin requires, you must know how long it takes your skin to burn when unprotected and exposed to sunlight. As a rule of thumb, anyone whose skin burns, whether or not it turns into a tan, should use an SPF of 15. Check with your doctor or pharmacist if you are taking antibiotics, antidepressants or antidiuretics. Some of these medications increase your skin’s sensitivity to sunlight and may decrease the time it takes your skin to burn.