We often only think about sun protection when it's sunny outside. But you still need to take steps to protect your skin even when it's overcast because the UV index can still cause lasting damage.
It's easy to assume that if it's not sunny outside then you don't need sunscreen - after all, you're not feeling the sun on your skin. But actually, you can still get sunburnt even when it's overcast and grey outside. It's the UV index that puts you at risk of burning, and that exists whether its bright and sunny or cloudy.
Rather that relying on what the weather looks like, or the temperature, when deciding if you need sunscreen you should be looking at the local UV forecast, according to Dr Walayat Hussain of the British Association of Dermatologists.
"If the UV index is three or higher, you should be protecting your skin,”" he reveals. "Your first line of defence should always be making use of shade, particularly between 11 am and 3 pm, wearing protective clothing and applying a sunscreen with a minimum 4-star UVA rating and an SPF of 30 or higher."
Don't fall into the trap of thinking you're safe in the shade, either. The sun's UV rays can reflect off sand, water or concrete and still cause damage to your skin. You can even get sunburnt when driving and skiing, so make sure you're always protected.
Why is UV dangerous for your skin?
Any time your skin is exposed to harmful UV rays you're at risk of sunburn, which not only causes aesthetic damage to your skin, like wrinkles, but also puts you at greater risk of skin cancer.
Every time your skin gets damaged by the sun it can cause mutations in your cells, which can lead to malignant tumours.
"The UV index is generally higher on cloudless, hot days; however, UV rays can still get through when it is completely overcast," Hussain says. "Although you are not more likely to get sunburnt when it's overcast, there is the risk of being lulled into a false sense of security when it is not obviously sunny.
"This can lead to sunburn on cloudy, cooler summer (and even spring) days. In the winter months, UV protection in the UK is very unlikely to be necessary except in people who are abnormally sensitive to sunlight."
UVA and UVB rays are the two main UV rays emitted by the sun. So you need to make sure you are protected from both. That means buying a sunscreen with a high enough SPF and a decent UVA star rating.
UVA rays account for up to 95% of UV radiation reaching the Earth's surface, according to the Skin Cancer Foundation. UVA penetrates the inner layer of the skin, called the dermis, and UVB mainly affects the outer layer of the skin, called the epidermis. Both can cause cancer.
How can you protect yourself?
"UVA is associated with causing premature skin ageing, whereas UVB is most responsible for causing sunburn. Both types of UV ray can cause skin cancer," Hussain adds.
"When choosing a sunscreen, it's important to choose one with both a high UVA rating and a high SPF, to ensure you're protected from both UVA and UVB rays."
Your risk of burning also depends on how long you'll be outside for.
If you work outside, or are planning on being outdoors all day, then you'll need more protection than someone who is just going for a quick walk. But you should always opt for a sunscreen with an SPF of 30 or more, and adequate UVA protection.
It's important to remember that sunscreen goes out of date, usually every year, so if it's past its use-by date it's less effective at protecting your skin from harmful UV rays. Make sure you always check the label.
Is the SPF in a moisturiser enough?
Some moisturisers and makeup provide an SPF, but be careful not to fall into the trap of thinking it's enough if you're outside all day.
You need to make sure every area of your skin exposed to the sun, or not covered by clothing, is protected with sunscreen.
"SPF moisturisers and foundation can provide adequate protection if you're not planning to be outside for long periods - for example, if you're just popping to the shops at lunchtime," Hussain points out.
"However, if you intend to spend time outdoors, particularly in the summer months, sunscreens are much more effective, not least because they tend to be applied much more thickly."
Skin cancer symptoms
Skin cancer is one of the most common cancers in the world.
In the UK, more than 100,000 new cases of non-melanoma skin cancer are diagnosed each year. It affects more men than women and is more common in the elderly.
Around 13,500 new cases of melanoma, the deadlier type of skin cancer, are diagnosed each year.
The most common symptoms to look out for include changes in the shape, colour, size, and edges of a mole; the formation of a new mole; and a mole on the skin that keeps bleeding.
Skin cancer can occur anywhere on the body, with most cases diagnosed in people under 50. Some 2,000 people die from melanoma each year in the UK.
If you have any of the above symptoms you should speak with a GP as soon as possible.