Based on their mechanism of action, topical sunscreens can be broadly classified into two groups, chemical absorbers and physical blockers. Chemical absorbers work by absorbing ultraviolet (UV) radiation and can be further differentiated by the type of radiation they absorb, UVA or UVB, or both UVA and UVB. Physical blockers work by reflecting or scattering the UV radiation. The most common physical blockers are titanium dioxide and zinc oxide.

Sunscreen can protect your skin against skin cancer and premature aging. However, it is not as effective unless it’s applied correctly. Follow these tips from dermatologists when applying sunscreen:

1. Choose sunscreen that has an SPF of 30 or higher, is water resistant, and provides broad-spectrum coverage, which means it protects you from UVA and UVB rays.
2. Apply sunscreen generously before going outdoors. It takes approximately 15 minutes for your skin to absorb the sunscreen and protect you. If you wait until you are in the sun to apply sunscreen, your skin is unprotected and can burn.
3. Use enough sunscreen. Most adults need at least one ounce of sunscreen, about the amount you can hold in your palm, to fully cover all exposed areas of your body. Rub the sunscreen thoroughly into your skin.
4. Apply sunscreen to all bare skin. Remember your neck, face, ears, tops of your feet and legs. For hard-to-reach areas like your back, ask someone to help you or use a spray sunscreen. If you have thinning hair, either apply sunscreen to your scalp or wear a wide-brimmed hat. To protect your lips, apply a lip balm with a SPF of at least 15.
5. Reapply sunscreen at least every two hours to remain protected, or immediately after swimming or excessively sweating.

People who get sunburned usually didn’t use enough sunscreen, didn’t reapply it after being in the sun, or used an expired product.

Your skin is exposed to the sun’s harmful UV rays every time you go outside, even on cloudy days and in the winter. So whether you are on vacation or taking a brisk fall walk in your neighborhood, remember to use sunscreen.