Why should you apply sunscreen every day?

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

Even today, most people continue to apply sunscreen irregularly. Many think it’s only useful during summer or prolonged sun exposure, such as beach tanning sessions or water sports. However, this protection isn’t limited to sunny days. The skin is exposed to UV rays far more often than you might think.

Even outside peak solar hours between 10 a.m. and 4 p.m., UV rays reach the skin’s surface at first light. Their presence does not depend on perceived heat or brightness: whenever natural daylight is present, exposure occurs. This also includes cloudy days, when up to 80% of UV rays can pass through the clouds, making sunscreen use relevant on overcast days.

Furthermore, UV exposure is not limited to outdoor settings. This seems counterintuitive. You should apply broad-spectrum sunscreen indoors because sunlight passes through windows. UVA rays, with greater penetration than UVB, pass through window glass and continue to affect the skin indoors. One study reported the case of a 65-year-old office worker showing pronounced photoaging on the left cheek, She remained exposed to sunlight through her office window for 15 years. The other side of her face, less exposed, showed minimal photodamage.

Similarly, motorists are exposed daily to significant doses of UVA radiation through side windows and windshields. A 2016 study found that windshields filter 96% of UVA on average. However, Repeated exposure is associated with increased skin lesions, photodamage, and skin cancer risk. These findings are supported by epidemiological data: a 2010 US study showed a predominance of skin cancers on the left side of the face (52.6%) in drivers in right-driving countries—corresponding to the side most exposed to the sun—compared with 47.4% on the right side.

These elements highlight the need for sun protection in settings that seem low risk, such as an office or a car.

Contrary to what you might think, applying a layer of sunscreen can make all the difference. Whatever your skin tone, applying sunscreen year-round, regardless of the seasons, helps protect skin from acute and chronic effects of UV exposure.

Sunscreen helps preserve the integrity of the skin barrier.

A short exposure without sunscreen – 15 minutes – can cause invisible, cumulative cellular damage.

UV rays weaken the skin’s natural barrier, increasing sensitivity to irritation, dryness, and inflammation. Daily sun protection strengthens the barrier’s protective function and limits sunburns. Sun exposure can worsen certain skin conditions, such as rosacea, eczema, and acne. Regular use of sunscreen helps prevent flares and supports daily care of these conditions.

Sunscreen helps delay premature skin aging.

80 to 90 percent of signs of premature skin aging are linked to chronic sun exposure.

UV rays damage Cellular DNA and proteins Structural proteins such as collagen and elastin. They generate free radicalsthat lead to local immune suppression and disrupt cell renewal. Over time, chronic exposure accelerates visible signs of skin aging. However, Adding sunscreen to your daily routine serves as a preventive measure against premature skin aging, supported by experimental and clinical evidence.

A 2013 randomized controlled trial involving 903 adults under 55 demonstrated that daily sunscreen application stabilized skin condition over the years, with no visible progression of skin aging, compared to the control group. These findings confirm the central role of daily sunscreen use in preventing visible signs of photoaging, including wrinkles, loss of firmness, vascular changes (telangiectasias), and pigmentary irregularities (age spots).

Beyond prevention, some research suggests that daily sunscreen may also help improve skin already altered by UV exposure. A 2016 study found that 33 women aged 40 to 55 who applied a broad-spectrum SPF 30 sunscreen for one year observed significant improvements in texture, clarity, and pigmentation. The existing signs of photodamage improved by 40 to 52% after 12 weeks, with continued gains through the 52nd week.

Sunscreen 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 cancers such as basal cell carcinoma, squamous cell carcinoma, and melanoma. Their impact is no longer limited to older adults: incidence is rising among young adults. By reaching the deeper skin layers, UV rays can cause DNA mutations in skin cells that may lead to cancer formation.

While avoiding sun exposure remains essential, daily sun protection is a key strategy for preventing skin cancer. It is recommended to apply a sufficient amount of broad-spectrum sunscreen with an SPF of at least 30 daily, regardless of skin phototype. Although fair skin types are at higher risk, darker skin tones are not immune to UV-induced cellular damage.

While several experimental studies in animals exposed to UV radiation have already clearly demonstrated the need for photoprotection to reduce skin cancer incidence, a 1999 Australian study involving 1,621 adults over four to five years, with an additional eight years of follow-up, showed that a daily application of SPF 15+ reduced by about 40% the risk of developing 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 sunscreen with a broad-spectrum SPF 17.

These results highlight the need for consistent protection even for darker phototypes. Though less prone to sunburn, they face the same 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).