Sunscreen: How to Choose It, How Much to Use and When to Reapply

What SPF, broad spectrum and water resistant mean; mineral or chemical; how much you need for face and body; when to reapply; and the mistakes that weaken protection even with the highest number.

Sunscreen · 3 min read · August 22, 2026

Written and medically reviewed by Dr. Yousef Abo Zarad · German board-certified dermatologist · Last reviewed: September 2026

Key takeaways

Choose a broad-spectrum, SPF 30+, water-resistant sunscreen.
Apply it to dry skin 15 minutes before going out, and reapply every two hours and after swimming or sweating.
Amount matters more than most people think: a shot glass for the body and a teaspoon for the face.
Mineral and chemical sunscreens both protect when broad-spectrum and SPF 30+; mineral suits sensitive skin better.
For melasma, pigmentation or darker skin, a tinted sunscreen with iron oxides adds visible-light protection.

Why do you need sunscreen?

Sunscreen helps prevent sunburn, reduces the risk of skin cancer, and helps prevent early signs of skin aging.

Everyone needs it, including people with darker skin, which can also burn and be damaged by the sun.

What do the words on the label mean?

Three things every sunscreen label should show
Label	Meaning	What to choose
Broad spectrum	Protects against both UVA and UVB rays	Always essential
SPF	Protection against burning UVB rays	30 or higher
Water resistant	Stays effective while swimming or sweating for a set time	40 or 80 minutes, then reapply

Mineral or chemical?

Mineral (physical) sunscreens contain zinc oxide, titanium dioxide or both, and are recommended for sensitive skin. Chemical sunscreens do not contain these ingredients. Both protect well when broad-spectrum and SPF 30+.

More important than the type is choosing a sunscreen you like on your skin, because you will use it daily and in the right amount.

Tinted sunscreen: for pigmentation and darker skin

Tinted sunscreen containing iron oxides adds protection against visible light, which is especially useful for darker skin and for melasma or pigmentation.

If you have melasma, the site's tinted mineral sunscreen guide explains what to look for in detail.

How much should you use?

Body: about one ounce, enough to fill a shot glass.
Face: at least one teaspoon, about enough to cover the length of your index and middle fingers.

Most people apply far less than needed, so their real protection falls below the number on the bottle.

When and how to apply it

Apply to dry skin 15 minutes before going outdoors; the skin needs that time to absorb it.
Use it every day on all exposed skin, not only on sunny days.
Cover the neck, face, ears, tops of the feet and legs.
Remember the easily missed spots: your back, your scalp if hair is thin, and your lips with an SPF 30+ lip balm.
Reapply every two hours, and right after swimming or sweating.

Sprays

Spray until the skin glistens, then rub it in well. Do not spray near the face or mouth, or near a flame.

Babies and children

Ideally, keep babies younger than 6 months out of the sun. If that is not possible, apply a minimal amount of mineral sunscreen to exposed areas.

Common mistakes that weaken protection

Applying too little.
Not reapplying after two hours or after swimming and sweating.
Relying on a high SPF number instead of amount and reapplication.
Missing the ears, neck, lips and scalp.
Using expired sunscreen.

Common questions

Does sunscreen block vitamin D? Get vitamin D from diet and fortified foods rather than unprotected sun exposure.
Do I need it indoors or on cloudy days? Apply it daily to exposed skin.
How long does it last? Sunscreens must keep their original strength for at least 3 years; discard it after the expiry date.
Is SPF 50 much better than 30? The difference in UVB protection is small; amount and reapplication matter more.