Sunscreen 101

Why sunscreen matters so much

Sun exposure is the largest controllable factor in visible facial ageing. Women with a sun-seeking history showed more wrinkles, sagging and uneven pigment, and the authors attributed most visible facial ageing to the sun (Flament et al., 2013). In identical twins, the twin with more sun exposure looked older (Guyuron et al., 2009). Sun protection also matters for skin-cancer prevention, a medical topic this guide does not cover; ask a doctor about any mole that changes.

Unlike many cosmetic steps, sunscreen has good direct evidence. In a randomised trial, adults assigned to daily broad-spectrum sunscreen showed no detectable increase in skin ageing over 4.5 years, unlike those who used it as they pleased (Hughes et al., 2013). If you are going to add one thing to your routine, this is it.

Decoding the label

SPF

SPF (sun protection factor) measures protection against UVB, the rays that cause sunburn. In lab conditions SPF 30 lets through about one thirtieth of UVB and SPF 50 about one fiftieth, so the jump from 30 to 50 is small. Applying enough matters more than chasing a higher number.

Broad-spectrum

This means the product also protects against UVA, the longer UV rays, and not only UVB. Look for the words broad-spectrum, and in some regions a UVA logo, PA rating or a star rating.

Water resistant

Water-resistant labels mean the product holds up for a stated time (such as 40 or 80 minutes) in water or sweat. No sunscreen is waterproof, so reapply after swimming and towel drying.

How much to use

Laboratory SPF values come from a thick test layer of about two milligrams per square centimetre. A thinner layer gives less protection than the label suggests, so apply generously.

• For the face and neck, use about two finger-lengths of cream, measured along your index and middle fingers.
• For the whole body, think a shot glass of lotion.
• Apply 15 minutes before going outside if you can, as a last skincare step in the morning.
• Do not forget ears, the sides and back of the neck, the tops of the feet and the hairline.
• Use a lip balm with SPF. Lips burn easily.

Mineral versus chemical

There are two families of UV filters. Both families are sold as effective when used as directed. Choose the one you will actually wear.

Chemical (organic) filters

These absorb UV and convert it to heat. They tend to be thin and clear on the skin, which many people find easier to wear daily. Some people find certain ones irritating around the eyes.

Mineral (inorganic) filters

Zinc oxide and titanium dioxide sit on the surface and reflect and scatter UV. Many people with sensitive skin prefer them, but they can leave a white cast, especially on deeper skin tones. Tinted versions can reduce that.

Choose by feel and finish. Try samples, test on your jaw for a day and keep the one you enjoy. A comfortable sunscreen you wear daily outperforms a perfect one that stays in the cupboard.

Common myths

• Dark skin does not need sunscreen. Skin of every tone can be affected by the sun. In one small study of people with darker skin, visible light caused darker, longer-lasting pigmentation than long-wave UVA (Mahmoud et al., 2010), which matters if dark marks are your concern. A dermatologist can advise on options.
• I am indoors, so I do not need it. If you spend long periods by a window or commute in daylight, it is sensible to wear it.
• Makeup with SPF is enough. Foundation is usually applied more thinly than the test layer behind the label, so it may fall short. Use sunscreen underneath.
• A base tan protects me. Tanning is not a safe shield. A sun-seeking history was linked with more wrinkles, sagging and uneven pigment (Flament et al., 2013).
• Cloudy days do not count. In the 4.5-year trial the sunscreen group applied it daily, not only when it was sunny (Hughes et al., 2013).

Making it a habit

1. Keep it next to your toothbrush or keys so you see it.
2. Make it the last step of your morning, every day, no exceptions.
3. Keep a small tube in your bag or desk for reapplication.
4. Choose a stick, mist or powder for reapplying over makeup.
5. Pair it with a hat and sunglasses on bright days.

If you use retinoids, which commonly cause irritation (Mukherjee et al., 2006), daily sunscreen is even more worthwhile. See retinoids for beginners.

Sunscreen and your face

Daily sunscreen protects the features people care about most. Faces with more even skin colour were judged younger, healthier and more attractive (Fink et al., 2006), and the daily-sunscreen trial found no detectable increase in skin ageing (Hughes et al., 2013). Pigment is one of several causes of dark circles (Vrcek et al., 2016).

LookFlex tracks skin zones such as tone, texture and redness across scans and warns you when lighting differs. Sunscreen's main benefit is long-term prevention, so don't expect it to show up within weeks. Start a free scan on your iPhone to set a baseline. The scan is a tracking tool and not a skin-cancer check. Have any worrying mark examined by a clinician.