Best sunscreen: how to choose one and how much to use

Sunscreen is the most useful product you can add to a routine, because sun exposure is behind most visible skin aging, many dark spots and most skin cancers. The best one is simply the one you will wear generously and often.

Quick answer: Choose a broad-spectrum, water-resistant sunscreen with SPF 30 or higher. Use about a teaspoon for the face and neck and about 1 ounce (a shot glass) for the body. Put it on about 15 minutes before going out, and reapply every 2 hours and after swimming or sweating. Pick a texture you enjoy, so you actually use it.

What do SPF, broad spectrum and water resistant mean?

These three phrases on the label tell you most of what you need to know.

• SPF (sun protection factor) shows how well the product protects against sunburn, which is mainly caused by UVB rays. The American Academy of Dermatology (AAD) recommends SPF 30 or higher. SPF 30 blocks most UVB rays, and higher numbers add only a little more, so a higher number is not a reason to skip reapplying.
• Broad spectrum means the product protects against both UVB and UVA. UVA rays reach deeper into the skin and are linked to skin aging and dark spots. The label must say "broad spectrum", because not every sunscreen is. In the UK, the NHS also suggests looking for at least a 4-star UVA rating.
• Water resistant means the sunscreen stays effective for 40 or 80 minutes while you swim or sweat, and the label must say which. No sunscreen is waterproof, so you still need to reapply.

Mineral or chemical sunscreen?

Sunscreens work with ingredients called UV filters. Mineral filters, zinc oxide and titanium dioxide, sit on the skin and block and scatter UV light. Chemical (organic) filters absorb UV light and turn it into a small amount of heat. Both types protect well when used properly.

Many modern formulas combine both types. If you have sensitive skin, a fragrance-free mineral formula is a sensible first try. The "best" type is the one that does not irritate you and that you will use daily.

How much sunscreen should you use?

Most people apply too little, and a thin layer gives less protection than the number on the bottle. The AAD gives these guides:

• Body: about 1 ounce (30 ml), the amount that fills a shot glass, to cover the exposed skin of most adults. The NHS gives a similar guide of around 6 to 8 teaspoons for the whole body. Larger bodies may need more.
• Face and neck: at least about a teaspoon, roughly the length of your index and middle fingers. Some other guides quote less for the face alone. If in doubt, apply a generous layer rather than a thin one.
• Often-missed spots: ears, the back of the neck, hairline, tops of feet and the parting in your hair. If your hair is thin, put sunscreen on the scalp or wear a wide-brimmed hat.
• Lips: use a lip balm with SPF 30 or higher.

Apply sunscreen to dry skin about 15 minutes before you go outside, as the AAD advises. The NHS suggests applying it 30 minutes before going out if you will be outside long enough to burn, and again just before you leave. You can browse body sunscreens and face sunscreens on Glowpedia.

How often should you reapply?

• Every 2 hours when you are outside.
• Right after swimming, sweating heavily or towel-drying, even with a water-resistant product.
• Sooner if you rub the area, for example with a bag strap or a hat.

If you are inside all day and not near bright windows, one morning application is often enough. UVA rays are present all year and can pass through window glass, so a daily habit still makes sense on cloudy days, in winter and when you sit by a window.

Reapplying over makeup is the hardest part. Options include a sunscreen stick or a generously applied spray. If you use a spray, apply it until the skin looks evenly coated and rub it in. Spray it away from your face, do not breathe it in, and keep it away from flames. Sunscreen powders are harder to apply in a protective amount, so many people use them as a top-up and not as their only layer.

Which texture suits your skin?

• Oily or acne-prone skin: gels, fluids and lotions labeled "non-comedogenic" (made not to clog pores).
• Dry skin: cream or lotion formulas with a moisturizing base.
• Sensitive or redness-prone skin: fragrance-free mineral formulas.
• Around the eyes: a stick is easy to control and less likely to run into the eyes.
• Medium to deeper skin tones: a formula that blends in with no white cast, or a tinted one. The AAD notes that a tinted sunscreen containing iron oxide may help prevent dark spots.

If you struggle with dark spots or melasma, a tinted mineral sunscreen with iron oxides is often suggested by dermatologists, because iron oxides help block visible light as well as UV.

Sunscreen on darker skin

Darker skin has more natural protection, but it is not complete. The NHS notes that people of all skin tones can get skin cancer, and sun exposure can darken existing marks. If a product leaves a gray or white cast, try a different texture or a tinted version instead of skipping it.

Sunscreen with other products

• Sunscreen last: in the morning, sunscreen goes after moisturizer, as the last skin-care step before makeup.
• Retinoids and exfoliating acids: these can make skin more sensitive to the sun, so use sunscreen every day. Read more in retinoids and sunscreen and exfoliating acids and sunscreen. The FDA specifically advises sunscreen with alpha hydroxy acid products.
• SPF moisturizers and foundations: fine as an extra layer, but most people do not apply enough of them to reach the label's SPF. Use a proper sunscreen layer underneath.
• Mixing sunscreen into other products: this dilutes it and makes the protection unpredictable. Apply it as its own layer.
• Old sunscreen: check the expiry date or the open-jar symbol with a number of months. Sunscreen kept in a hot car or beach bag may not work as well.

Common mistakes

• Using a thin layer, or skipping the neck, ears and hands.
• Relying on sunscreen alone. Shade, a hat and clothing also help, and sunscreen should not be used to stay in the sun longer.
• Putting it on only when it is sunny or hot.
• Believing that a high SPF means you can skip reapplication.
• Using sunscreen from last summer without checking whether it is expired.

Worried about vitamin D? Ask your doctor, who can check your level and advise on food or supplements. Skipping sunscreen is not a safe way to get it.

When to see a dermatologist

• A rash, hives, burning or swelling after using a sunscreen. You may react to a single ingredient, such as a filter or a fragrance, and a doctor can help find it.
• A new spot, or a mole or spot that changes in size, shape or color, itches, bleeds or does not heal.
• A bad sunburn with blisters, fever, chills or severe pain.
• Dark patches that appear or worsen in the sun, which could be melasma or another condition.

FAQ

Is SPF 100 better than SPF 50?

Only slightly. Higher SPF numbers add a little protection, but not enough to replace reapplying, shade and clothing.

Do I need sunscreen on cloudy days or in winter?

Yes. UVA rays are present all year and can pass through clouds and window glass. A daily morning layer is a good habit.

Can babies and children use sunscreen?

Keep babies under 6 months in the shade and in covering clothing, and ask a pediatrician before using sunscreen on them. From 6 months, the AAD and NHS both advise broad-spectrum sunscreen with SPF 30 or higher on skin not covered by clothing. Mineral formulas tend to be gentler.

Is spray sunscreen enough?

It can work if you apply enough and rub it in, but it is easy to miss patches. Many people apply a spray into their hands for the face and do not breathe it in.

Does a higher price mean better sunscreen?

No. What matters is the SPF, broad-spectrum label, the amount you apply and how often you reapply.

Sources

• Sunscreen: How to Help Protect Your Skin from the Sun (FDA)
• Questions and Answers: FDA's regulatory actions on over-the-counter sunscreen (FDA)
• How to apply sunscreen (American Academy of Dermatology)
• How to select a sunscreen (American Academy of Dermatology)
• Infant sun protection: how parents can keep their baby safe (American Academy of Dermatology)
• Sunscreen and sun safety (NHS)