How Do I Choose and Use Sunscreen?

The bottle in your bag says SPF 50 and “waterproof.” You put a coin-sized dab on your face, then went on a four-hour walk. By dinner your nose and the part in your hair are pink. You assumed the number did the work.

What the label means

The FDA² says broad spectrum products protect against both UVA and UVB radiation, while SPF mainly measures UVB protection. The AAD¹ says SPF 30 blocks about 97% of UVB rays.

On “waterproof,” the FDA² says there’s no such thing. A product labeled water resistant must state whether it keeps its protection for 40 minutes or 80 minutes of swimming or sweating.

How much and how often

• Amount. The AAD¹ says adults should use about 1 ounce, roughly enough to fill a shot glass, and at least a teaspoon for the face. The FDA² says at least one ounce to cover the body from head to toe.
• Timing. The AAD¹ says to apply it to dry skin 15 minutes before going outdoors.
• Reapplying. The AAD¹ says about every two hours, or after swimming or sweating. The FDA² says at least every two hours and more often if you’re swimming or sweating.

What sunscreen can’t do alone

The AAD¹ says sunscreen alone is insufficient. It recommends shade during peak sun hours, long sleeves, pants, a wide-brimmed hat, UV-blocking sunglasses, and avoiding tanning beds. The CDC³ lists the same: stay in the shade, cover your arms and legs, wear a hat with a wide brim to shade your face, head, ears and neck, and use sunglasses that wrap around and block both UVA and UVB. It says to apply plenty of sunscreen to all exposed skin, including the ears and the back of the neck, and that UV rays are strongest between 10 a.m. and 4 p.m. daylight saving time.

The AAD¹ and FDA² both use 10 a.m. to 2 p.m. as the peak window. Plan outdoor time around whichever applies where you live.

The CDC³ says indoor tanning beds expose users to intense levels of UV rays, a known cause of cancer.

Babies

The FDA² says sunscreen is not recommended for infants under six months old. The AAD¹ says to keep them in the shade and use protective clothing. Ask a pediatric clinician.

For what sun exposure shows up as later, see age spots, dark patches on the face, skin aging and checking your skin.

The play

Try this: a sunscreen-ready kit

Keep sunscreen accessible for your routine, protected from excessive heat and direct sun, as the FDA² advises.

Measure once. Squeeze a teaspoon onto your fingers, which is the AAD’s¹ amount for your face, and see how much that is.

Set a two-hour reminder on days you’re outside, and add a hat.

When to get checked

Book an appointment if any of these fit:

• A new spot, or an old spot that’s changing, itching or bleeding. See the self-exam article.
• You’ve had many sunburns or used tanning beds and have never had a skin check
• You react to sunscreen with a rash. See contact dermatitis.
• You’re not sure which sunscreen suits your skin

A number on a bottle doesn’t protect you. Amount, reapplication and shade do.