Sunscreen is often associated with summer, holidays and bright sunshine. Yet ultraviolet (UV) radiation is present throughout the year, including on days when the sky is overcast.
Understanding how UV radiation affects the skin, and what sunscreen can realistically do, makes it easier to establish sensible sun protection habits without unnecessarily complicating your skincare routine.
Understanding UVA and UVB radiation
The sun emits different forms of radiation. Two types of ultraviolet radiation reach the Earth's surface and are particularly relevant to skin health: UVA and UVB.
UVB radiation is the main cause of sunburn. Its intensity varies considerably according to the time of day, season, latitude and atmospheric conditions. In the UK, UVB exposure is generally highest around the middle of the day during spring and summer.
UVA radiation penetrates more deeply into the skin and contributes to visible signs of photoageing, including changes in pigmentation, texture and elasticity. Both UVA and UVB can damage DNA and contribute to skin cancer risk.
UVA is present throughout daylight hours and across the seasons, although its intensity is not constant. Cloud cover can reduce UV exposure, but it does not necessarily eliminate it.
This is why the temperature or brightness of the day is not always a reliable indication of UV exposure.
Do you need sunscreen on cloudy days?
Clouds can reduce the amount of ultraviolet radiation reaching the ground, but the effect varies with their thickness and coverage. Significant UV exposure is still possible when the sun is obscured.
A more useful guide is the UV Index, which measures the intensity of sunburn-producing ultraviolet radiation at the Earth's surface.
In the UK, the NHS recommends taking additional precautions when the UV Index is 3 or higher, particularly if you are spending time outdoors.
You can check the daily forecast using the Met Office UV Index.
For people with conditions that are aggravated by sunlight, including rosacea, daily sunscreen may be advisable even when the UV Index is lower.
What about UVA exposure through windows?
Ordinary window glass blocks most UVB radiation, but some UVA can pass through it.
The amount transmitted depends on the type of glass, whether it has a protective coating, and your position relative to the window.
For most people, occasional time spent indoors near a window is not equivalent to prolonged outdoor sun exposure. However, people who spend extended periods beside large windows receiving direct sunlight may wish to consider additional protection.
The important distinction is between possible exposure and meaningful exposure. Not every indoor situation presents the same level of risk.
What does SPF actually measure?
SPF stands for Sun Protection Factor. It describes the level of protection a sunscreen provides against the ultraviolet radiation responsible for sunburn, primarily UVB.
An SPF 30 sunscreen provides greater protection than SPF 15, while SPF 50 provides greater protection than SPF 30.
However, SPF is measured under controlled laboratory conditions using a specified quantity of product. The protection achieved in everyday use depends on applying enough sunscreen, distributing it evenly and reapplying it when necessary.
It is also important to understand that SPF is not a timer.
For example, SPF 30 does not mean you can safely remain in the sun for 30 times longer than you otherwise would. UV intensity changes throughout the day, and sunscreen protection is affected by factors including application, sweating, swimming and rubbing.
Understanding UVA protection
SPF alone does not tell you how much UVA protection a sunscreen provides.
When choosing sunscreen in the UK, the NHS recommends a product with at least SPF 30 and a UVA rating of four stars or higher.
The UVA star-rating system indicates the balance of UVA protection relative to UVB protection. A higher star rating indicates a better balance, rather than an absolute measure of UVA protection.
You may also see the letters UVA inside a circle on sunscreen packaging. This symbol indicates that the product meets the relevant standard for UVA protection relative to its labelled SPF.
Looking for both an appropriate SPF and clear UVA protection information helps you make a more informed choice.
How much sunscreen should you apply?
Even a well-formulated sunscreen cannot provide its labelled protection if too little is applied.
For adults, the NHS advises approximately six to eight teaspoons of sunscreen to cover the entire body, although the amount required depends on body size and the areas exposed.
For the face, neck and ears, follow the manufacturer's application instructions and ensure all exposed areas are covered evenly. Commonly missed areas include the ears, hairline and back of the neck.
Sunscreen should be applied generously before going outdoors and reapplied at least every two hours during continued sun exposure, as well as after swimming, sweating or towel drying, even when the product is described as water-resistant.
If you use moisturisers or serums, apply these first and allow them to settle before applying sunscreen as the final skincare step.
Is sunscreen necessary if your skin is sensitive or prone to rosacea?
Sun exposure is a recognised trigger for rosacea and may contribute to episodes of flushing and redness.
The NHS recommends wearing sunscreen with at least SPF 30 every day as part of managing the condition.
Finding a suitable formula can take some experimentation, particularly when skin is sensitive or easily irritated.
Fragrance-free products may be preferable for some people, while the texture and finish can influence how comfortable a sunscreen feels throughout the day.
The most useful sunscreen is one that provides appropriate protection, suits your skin and can be applied consistently in the recommended amount.
Sunscreen is only one part of sun protection
Sunscreen is an important part of protecting your skin, but it should not be relied upon in isolation.
Seeking shade during periods of strong sunlight, wearing protective clothing and using a wide-brimmed hat can help reduce UV exposure.
These measures are especially important during prolonged outdoor activities or when the UV Index is high.
Sunscreen should complement these precautions rather than encourage longer periods in direct sunlight.
Making sun protection part of your routine
An effective skincare routine does not need to be complicated.
Cleanse as needed, apply your preferred treatment products and moisturiser, then finish with a suitable broad-spectrum sunscreen in the morning.
Antioxidant skincare ingredients, including vitamin C, may complement a routine focused on maintaining healthy-looking skin, but they do not replace sunscreen or provide a measurable SPF unless the finished product has been specifically tested and labelled for sun protection.
For most people, the aim should be a straightforward routine that is comfortable enough to maintain consistently.
A considered approach to sun protection
Sun protection is not simply a summer concern. Understanding UVA and UVB radiation, choosing an appropriate sunscreen and applying it correctly can help reduce the effects of excessive UV exposure.
For everyday use, look for at least SPF 30 with good UVA protection, pay attention to the UV Index and use clothing and shade when needed.
The most effective approach is not necessarily the most elaborate. It is one that is appropriate for your circumstances and easy to maintain.
