Cloudy days, real damage: How much light penetrates winter skies?

Even when the sky is thick with clouds, UVA radiation still reaches the skin and causes deep damage. Unlike UVB rays, which are strongest in the summer months, UVA remains present and harmful all year round. Wearing sun protection every day is not just about preventing sunburn - it’s about maintaining skin health across all seasons.

Why cloudy days feel ‘safer’ for skin

After the heat of the summer, cloudy skies signal a change of the seasons. Clouds are synonymous with cold temperatures and wet weather, and when we see grey skies, we are much more likely to reach for scarves and raincoats than sun protection.

But cloud coverage offers a false sense of security in terms of sunlight and light-induced damage.

Without the glare of the sun, daily sun protection is easily forgotten. Many people assume that if they can’t feel warmth or see bright skies, their skin is safe. Behaviourally, these sun protection myths translate into fewer SPF applications or skipping sun protection altogether.

But the visible intensity of sunlight is not a reliable indicator of biological risk. Visual brightness and UV exposure are separate variables, and the skin is still at risk of damaging UVA rays even when the sun is obscured by cloud coverage.

What actually happens to sunlight when it hits cloud cover

When light from the sun hits clouds, it scatters, reflects or partially passes through.

Cloud droplets, which are much larger than air molecules, scatter all visible wavelengths fairly evenly, which is what makes clouds appear white or grey. Thin, wispy clouds filter a fraction of incoming radiation, allowing most ultraviolet and visible light to pass through. Thick, heavy clouds can reduce UVB more noticeably, but a significant portion of UVA remains. Only a small fraction of sunlight is absorbed.

Studies have shown that clouds may reduce total UV radiation slightly, depending on thickness, but they rarely block it entirely. Visible light penetration acts similarly, so even though we can’t see or feel sunlight, the skin continues to absorb radiation.

Does UVA penetrate clouds?

UVA rays have a wavelength of between 320 and 400 nanometers. They are less energetic than UVB rays, but they penetrate clouds, glass and deep skin layers more powerfully.

Clouds may reduce, but will never completely eliminate, UVA radiation. The rays are less easily absorbed or scattered, and will continue to have a strong presence, regardless of cloud cover. Throughout winter, UVA intensity remains substantial, even as temperatures drop and daylight hours reduce.

This can be misleading when it comes to sunscreen application, even for those who would be otherwise strict with SPF in the summer. Cold or grey conditions suggest safety, yet UVA still contributes to photoageing, pigmentation changes and cumulative oxidative stress. The skin’s lack of immediate redness under such exposure reinforces these misconceptions.

What about visible light and infrared-A on cloudy days?

Visible light and infrared-A (IRA) also penetrate clouds. No matter the weather, the energy from these wavelengths will reach the skin and pose a number of risks to skin health. This includes free radical damage and oxidative stress, premature skin ageing, DNA damage, excessive melanin production, a reduction in collagen and elastin production, and a weakened skin barrier function.

Winter clouds may dim the view, but they do not stop the full spectrum of light from harming the skin.

Why you can still accumulate skin damage without seeing the sun

Even in the autumn and winter, UVA radiation and visible light will penetrate the atmosphere and cloud coverage, reaching the skin and triggering oxidative stress. In the skin, these reactive oxygen species (ROS) accelerate collagen breakdown and weaken the skin’s structure. Melanin production is also disrupted, which can lead to pigmentation and uneven skin tone. Unlike UVB radiation, UVA rays penetrate the skin more deeply and exert subtle but cumulative effects. And it is these cumulative exposure that drive long-term skin ageing. In fact, multiple low-dose UVA exposures have been linked to significant dermal and epidermal histological changes, which in the most serious cases lead to skin cancer.¹

So even when the sun isn’t shining brightly, regular low-level light intake of light, whether through clouds, windows or reflected surfaces, will accumulate and cause long-term damage.

Cloudy day myths: What people get wrong

There are many sun protection myths that can undermine protective behaviours. These can include the misconception that you can’t burn on cloudy days, you can’t burn in the winter sun, and indoor sun exposure doesn’t count.

Each of these misconceptions underestimates the power of UVA radiation and visible light. Cloud cover may reduce UVB enough to prevent immediate redness, but UVA rays remain active and harmful, meaning the skin will continue to absorb damaging energy.

Why dermatologists still recommend daily protection on overcast days

High-level, full-spectrum protection on cloudy days is recommended for several reasons.

"Cloud cover often creates a false sense of safety, but it does not block the wavelengths of light that drive long-term skin damage." says Dr Amy Perkins. "Daily broad-spectrum protection supports skin health across all skin tones by reducing cumulative oxidative stress, photoageing and pigmentation changes. While the risk of skin cancer is highest in lighter skin tones, sunscreen use goes far beyond cancer prevention and benefits everyone."

Adequate sun protection extends beyond sunburn, and considers all things skin health, from its structural integrity and skin barrier function, to visible signs of ageing like wrinkles, dullness and pigmentation.

A consistent approach will make for the gradual but meaningful prevention of photoageing. When we apply sun protection every single day, we care for the skin in so many ways. Collagen and elastin production is stabilised, pigmentation disorders are mitigated, barrier function is maintained, and cumulative oxidative stress is reduced.

Clouds change what you see, not what your skin receives

Grey skies might alter our perception of sunlight, but exposure is still a risk. UVA rays and visible light will still penetrate cloud coverage, contributing to photoageing, oxidative stress and skin health risks. That’s why daily sun protection is a must, even when it’s cold and cloudy outside.

For reliable protection against light-induced damage all year round, choose HELIOCARE 360°. Our award-winning range of dermatological sun protection is designed to defend the skin against the full spectrum of light, including UVA rays. It is widely regarded as one of the most comprehensive sun protection ranges available, delivering extremely high-level protection that extends beyond conventional SPF.

At the core of the HELIOCARE 360° is Fernblock®+, a clinically-proven antioxidant technology that protects against multiple forms of light-induced damage, while strengthening the skin’s natural defences from within. The HELIOCARE 360° range is further boosted by ASPA-Fernblock®, a next-generation bioactive complex and the latest evolution in skin photoprotection. ASPA- Fernblock® ensures your skin only gets the very best from the sun, featuring two patented technologies that protect and support skin health whilst boosting the efficiency of UV filters (including UVA) and preserving the skin’s natural ability to receive and use vitamin D.

As a daily strategy, HELIOCARE 360° provides complete protection against sun damage and premature skin ageing. Recognising that no two skin types are the same, the range includes a wide variety of formulations tailored to different skin concerns, sensitivities and indications, ensuring effective protection for every skin type, every day.

Cloud cover may soften the view, but it does not soften the impact. Wearing high-level, full-spectrum sun protection like HELIOCARE 360° is the most reliable strategy for reducing cumulative damage and protecting the skin, all year round.