Rumour: “You don’t need sunscreen in winter or on cloudy days” — What does the science say?

Short answer: sun protection is often needed in winter and on cloudy days too. Clouds do not block all ultraviolet rays; snow increases exposure by reflecting light. The UVA rays that age the skin are present all year round and can pass through window glass. In the winter months, the intensity of the sun’s rays is generally lower than in summer; however, protection is especially important for people prone to pigmentation such as melasma, for those who have recently had a medical aesthetic procedure, and for those who spend time in snowy or high-altitude places.

What is in sunlight?

The ultraviolet (UV) rays that come from the sun fall into two main groups as far as the skin is concerned. UVB rays mainly affect the surface of the skin and are the main cause of sunburn. Their intensity varies markedly with the season, the time of day and geographical location; it decreases in winter.

UVA rays, on the other hand, reach the deeper layers of the skin. They play an important role in sun-related skin ageing, such as wrinkles, loss of elasticity and pigmentation. The intensity of UVA does not fluctuate with the seasons as much as UVB. Both types of rays are linked to skin cancer risk.

Do clouds block the sun?

Clouds reduce the sun’s heat and brightness more than we sense; they do not block ultraviolet rays nearly as effectively. The World Health Organization states that a thin layer of cloud can allow most UV rays to pass through. Thick, dense clouds give more protection.

Because the sun does not feel strong on a cool, cloudy day, people may stay outdoors unprotected for longer. This can lead to unexpected sunburn and, over time, to accumulated sun damage.

Is sunlight still effective behind glass?

Standard window glass blocks most UVB rays but lets a significant proportion of UVA rays through. Medical publications have reported that people who work next to a window for long periods or drive long distances every day can show more pronounced sun damage on the side of the face and arm that faces the window.

For this reason, if you sit next to a window all day or drive for long periods, it may be helpful to consider sun protection in the winter months too.

Snow and altitude increase exposure

Fresh snow reflects most ultraviolet light. This means the skin is exposed to light coming both from above and from below. In addition, as altitude increases, the filtering effect of the atmosphere decreases and the intensity of UV rays rises.

During activities such as skiing or mountain hiking, serious sunburn can occur even though it is winter. In these environments, it is important to protect not only the skin but also the eyes with suitable sunglasses.

Who should be more careful in winter?

• People with melasma or a tendency to pigmentation: melasma can darken even with low levels of sunlight. Visible light is also thought to be able to affect melasma. For details, see our article “Dark Spots and Melasma”.
• People who have recently had laser, a chemical peel or a similar procedure: after a procedure, the skin is more sensitive to the sun, and unprotected sun exposure can increase the risk of pigmentation. For general principles, see the article “Aftercare Following Medical Aesthetic Procedures”.
• People having a course of laser hair removal: tanned skin increases the risk of burns and colour changes. The details are in our article “Laser Hair Removal”.
• People taking medicines that can cause sensitivity to light: some antibiotics, some medicines used to treat acne and other medicines can make the skin sensitive to the sun. Ask your physician or pharmacist about this for your medicine.
• People who have had skin cancer before, or people with fair skin who burn easily

How do you protect yourself from the sun in winter?

As a practical guide, the World Health Organization recommends sun protection when the UV index is 3 or above. The UV index can be found in weather apps and weather services. In the winter months, at sea level, this value may be low on most days; in the mountains, on snow and around midday, however, it can rise.

1. Check the day’s UV index; take particular care in snowy and high-altitude areas.
2. If you will be spending time outdoors, apply a broad-spectrum (against UVA and UVB) sunscreen to exposed areas such as the face, ears and hands.
3. If you are outdoors for a long time, reapply sunscreen at the intervals recommended by your physician or the product instructions.
4. Support sunscreen with a hat, sunglasses and suitable clothing.
5. If you have melasma or have recently had a procedure, discuss a personal protection plan with your physician.

Conclusion

The rumour that you don’t need sunscreen in winter or on cloudy days comes from not feeling the sun’s heat. Yet a significant proportion of UV rays pass through clouds, UVA can also get through window glass, and snow increases exposure. The level of protection needed on winter days varies with the person, where you are and what you are doing. If you have a tendency to pigmentation or have recently had a procedure, it is advisable to set your protection plan together with your physician.