How does sunscreen help your skin?

How does sunscreen protect your skin?

Sunscreen filters ultraviolet radiation before it damages your skin. UVA reaches deeper into skin and is mainly associated with lasting damage such as wrinkles. UVB mainly affects the outer layer and is the main cause of sunburn. Both contribute to premature aging and skin cancer. That premature aging is called photoaging: damage from repeated UV exposure, rather than aging determined by your age and genetics.34

Regular sunscreen use helps prevent wrinkles, dark spots and sagging caused by UV exposure. Daily use of SPF 15 or higher can reduce melanoma risk by 50% and squamous cell carcinoma risk by 40%. These are two types of skin cancer; the figures describe risk reduction, not complete protection.3

What results should you expect?

The useful result is less damage accumulating, which is less photogenic than a before and after picture but a better job description. Sun protection helps reduce sunburn and premature aging, including age spots, sagging and wrinkles. If you have already had skin cancer, sun protection can also reduce the risk of another skin cancer.5

Sunscreen helps prevent further damage rather than undoing existing damage, so it is not a time machine for your face. UV damage to skin cell DNA cannot be reversed. Existing wrinkles, discoloration and roughness can be improved with separate treatments, even though sun damage cannot be completely reversed. Natural aging also continues; sunscreen targets the additional aging caused by UV exposure.4

What sunscreen should you choose?

Choose SPF 30 or higher with broad spectrum protection and water resistance. SPF measures protection against UVB and sunburn; broad spectrum means protection against both UVA and UVB. A higher SPF offers more UVB protection, but the SPF number alone does not tell you whether a sunscreen protects against UVA. No sunscreen blocks all UV rays, so use shade, protective clothing, a hat and sunglasses alongside it.13

Mineral, chemical and hybrid sunscreens all form a protective layer that absorbs the sun's rays; mineral sunscreens also reflect them. For sensitive skin, mineral sunscreen containing zinc oxide or titanium dioxide is a useful choice. Creams suit dry skin, while gels suit oily skin and hairy areas. A tinted sunscreen with iron oxide adds protection against visible light, which can worsen pigmentation, especially in darker skin tones.1

How do you apply sunscreen properly?

1. 1Apply sunscreen every day you will be outside, including cloudy days. Apply it to dry skin 15 minutes before going outdoors.
2. 2Cover skin not protected by clothing. Most adults need at least about 1 ounce for exposed skin, depending on body size, and at least 1 teaspoon for the face.
3. 3Include your ears, neck, tops of your feet and exposed scalp. Protect your lips with SPF 30 or higher lip balm.
4. 4Reapply approximately every two hours outdoors and after swimming or sweating. Also reapply after towel drying or whenever sunscreen has rubbed off.

Applying sunscreen too thinly reduces its protection. For prolonged sun exposure, NHS guidance is to apply it 30 minutes before leaving and again just before going out. Water resistance does not remove the need to reapply after swimming. Check the expiry date, too: expired sunscreen or improper storage can make protection less effective.36

Does sunscreen help with dark marks?

Post inflammatory hyperpigmentation means darkening left after skin inflammation or injury, including acne. UV and visible light can worsen these marks. Sun protection reduces that exposure and is part of managing pigmentation, but sunscreen is not an active pigment removal treatment. Some deeper pigment can persist for years, so preventing further darkening and clearing an existing mark are different jobs.7

A small randomized trial in 20 adults with medium to dark skin tested one broad spectrum sunscreen containing sclareolide and niacinamide. Daily application for 20 days reduced darkening on test areas exposed to UV and visible light, including areas with mild barrier disruption. That supports prevention of new pigmentation with that formula, rather than a deadline for clearing existing acne marks.2

Does sunscreen help you tan?

Sunscreen is for protection, not safer tanning. There is no safe or healthy UV tan, and a tan does not protect skin from the sun's harmful effects. Do not use sunscreen as a reason to stay in the sun longer.6

Does sunscreen help with post inflammatory erythema?

Post inflammatory erythema means redness remaining after inflammation. Sunscreen protects against additional UV damage, but whether it clears established red acne marks remains uncertain. The trial of sunscreen with sclareolide and niacinamide found less redness after controlled light exposure and barrier disruption. Redness induced on test areas is different from persistent acne marks, so use sunscreen for protection rather than expecting a proven redness treatment.2

Who needs extra care?

All skin tones are susceptible to sun damage, even when burning is less likely. Some medicines increase sensitivity to sunlight, while immune suppressing medicines and certain medical conditions increase the risk of sun damage. Ask your pharmacist or prescriber whether your medicines change the precautions you need.4

Keep babies under 6 months out of direct strong sunlight. If sunburn causes severe swelling, blisters or feeling unwell, seek medical help. Stay out of the sun until redness has gone. Report a new mole, growth or lump, or a patch that changes size, shape or colour, to your doctor promptly.6