Why is it necessary to apply sunscreen every day?

Anyone older than six months should apply a broad-spectrum sunscreen with an SPF of 30 or higher every day to sun-exposed areas.

Even today, most people continue to use sunscreen irregularly. Many assume it is only needed in summer or during prolonged sun exposure, such as beach sunbathing or water sports. However, this protection is not limited to sunny days. Skin is exposed to UV radiation far more often than you realise.

Outside periods of peak solar intensity, from 10 am to 4 pm, UV rays reach the skin’s surface at first light. Their presence does not depend on perceived heat or brightness: where there is natural light, exposure occurs. This applies on cloudy days, when up to 80% of UV rays can pass through the clouds, making sunscreen use relevant in overcast conditions.

Moreover, UV exposure is not limited to outdoor settings. It may appear counterintuitive, but applying a broad-spectrum sunscreen indoors is advisable, as sunlight still passes through windows. UVA rays, which penetrate more deeply than UVB, pass through glass and continue to affect skin indoors. One study reported a case of a 65-year-old office worker with pronounced photoageing on her left cheek, who spent 15 years exposed to sunlight through her office window. The other side of her face, less exposed, showed almost no signs of photodamage.

Similarly, motorists are exposed daily to significant doses of UVA radiation through side windows and windscreens. A 2016 study found that windscreens filter on average 96% of UVA rays. However, This repeated exposure is linked to increased skin lesions, photodamage, and the risk of skin cancers. These findings are supported by epidemiological data: a 2010 US study showed skin cancers predominated on the left side of the face (52.6%) among drivers in countries where people drive on the right, corresponding to the side more exposed to the sun, compared with 47.4% on the right side.

These factors highlight the need for sun protection even in low-risk settings, such as in an office or in a car.

Contrary to common belief, applying a layer of sunscreen can make a meaningful difference. Whatever your skin colour, wearing sunscreen year round, regardless of season, helps protect skin from the acute and chronic effects of UV exposure.

Sunscreen helps preserve the integrity of the skin barrier.

Brief unprotected sun exposure – 15 minutes only – can cause invisible yet cumulative cellular damage.

UV rays weaken the skin’s natural protective barrier, making it more susceptible to irritation, dryness, and inflammation. Daily photoprotection is one of the most effective ways to limit sunburn by reinforcing the skin barrier’s protective function. In addition, sun exposure can aggravate certain dermatological conditions, such as rosacea, eczema, and acne. Regular sunscreen use helps prevent flare-ups and supports daily management of these conditions.

Sunscreen helps delay premature skin ageing.

80 to 90% of signs of premature skin ageing are linked to chronic sun exposure.

UV radiation damages cellular DNA and proteins structural proteins such as collagen and elastin. They also trigger free radical formation, causing local immune suppression and impaired cellular renewal. In the long term, chronic exposure accelerates the appearance of visible signs of skin ageing. However, incorporating sun protection into a skincare routine is an effective preventive measure against premature skin ageing, supported by experimental and clinical evidence.

A 2013 randomised controlled trial conducted on 903 adults under the age of 55, showed that daily application of a sunscreen stabilised skin condition over the years without visible worsening of skin ageing, unlike the control group. These results confirm the central role of daily use of a sunscreen in the prevention of visible signs of photoageing, in particular wrinkles, loss of firmness, vascular disorders (telangiectasias) and uneven pigmentation (age spots).

Beyond prevention, some research suggests that daily sun protection may help to improve the condition of already photodamaged skin. A 2016 study found that 33 women aged 40 to 55 who applied a broad-spectrum SPF 30 sun cream for one year showed significant improvements in texture, clarity, and pigmentation. The existing signs of photodamage improved by 40 to 52% as early as 12 weeks, with continued progress through the 52nd week.

Sun cream reduces the risk of skin cancer and precancerous skin lesions.

According to Santé Publique France, more than 85% of skin cancers are attributable to excessive UV exposure.

UV rays are the main risk factor for skin cancer, such as basal cell carcinoma, squamous cell carcinoma, and melanoma. Their impact is no longer limited to older populations: incidence is rising among young adults. By penetrating deep into the skin, UV rays can cause DNA mutations in skin cells, which may lead to the formation of cancerous cells.

If avoiding sun exposure remains essential, daily sun protection is a key strategy to prevent skin cancer. We recommend applying an adequate dose of broad-spectrum sunscreen with an SPF of at least 30 every day, regardless of phototype. Although fair skin types carry greater risk, darker skin is not exempt from UV-induced cellular damage.

While several experimental studies on animals exposed to UV radiation have already clearly demonstrated the need for photoprotection to reduce skin cancer incidence, a 1999 Australian study of 1,621 adults over four to five years, with an additional eight years of follow-up, found that daily application of an SPF 15 sunscreen+ reduced ofaround 40 per cent the risk of developing a squamous cell carcinoma. Similarly, a 1993 clinical trial of 588 Australians with actinic keratoses showed a significant reduction in the occurrence of new actinic keratoses (precancerous lesions), after a summer of regular use of a broad-spectrum sunscreen with SPF 17.

These findings highlight the importance of constant protection, even for darker phototypes, less prone to sunburn but equally affected by the long-term effects of sun exposure.

• MARKS R. & al. Reduction of solar keratoses by regular sunscreen use. New England Journal of Medicine (1993).

• FIERE A. & al. Un cas unilateral d’élastose avec kystes et comédons de Favre et Racouchot. Annales de Dermatologie et de Vénéréologie (1994).

• RUSSELL A. & al. Daily sunscreen application and betacarotene supplementation in prevention of basal-cell and squamous-cell carcinomas of the skin: a randomised controlled trial. Lancet (1999).

• FOSKO S. W. & al. Increased prevalence of left-sided skin cancers. Journal of the American Academy of Dermatology (2010).

• GREEN A. C. & al. Sunscreen and prevention of skin aging: a randomized trial. Annals of Internal Medicine (2013).

• PIOT B. & al. Effect of the sun on visible clinical signs of aging in Caucasian skin. Cosmetic and Investigational Dermatology (2013).

• WHITEMAN D. & al. Cancers in Australia attributable to exposure to solar ultraviolet radiation and prevented by regular sunscreen use. Australian and New Zealand Journal of Public Health (2015).

• WACHLER B. S. B. Assessment of levels of ultraviolet a light protection in automobile windshields and side windows. JAMA Ophthalmology (2016).

• SOUTHALL M. D. & al. Daily use of a facial broad spectrum sunscreen over one-year significantly improves clinical evaluation of photoaging. Dermatologic Surgery (2016).

• WHITEMAN D. C. & al. How many melanomas might be prevented if more people applied sunscreen regularly? British Journal of Dermatology (2018).