How to know it’s time to put on sunscreen

Young girl in straw hat is applying sunscreen on her back to protect her skin.
Sunscreen is vital on a hot day to ward off burns. (Getty Images)

Only “mad dogs and Englishmen go out in the midday sun”, or so the saying goes.

Temperatures have soared to near-record levels for June, with parts of the UK basking in over 30C (86F) – hotter than Ibiza and the Bahamas.

Read more: What a heatwave does to the body

With sunny days few and far between, photographs have emerged of Britons flocking to the beach.

While the sun provides vital vitamin D, the Met Office has warned its UV rays are “very high”, leaving many at risk of painful burns that raise the risk of skin cancer.

The good news is the warm weather can be enjoyed safely, so long as you know when it’s time to load up on sunscreen.

‘Tanning signifies damage has occurred’

People with different skin tones and hair colours vary in their susceptibility to damage from UV rays, with pale redheads burning easily.

While often associated with exotic holidays, it is possible to burn in the UK, even if it is cloudy or you feel a gentle breeze.

If the weather feels warm, you are outside for a prolonged period of time or the Met Office has warned the UV rays are high – generally a score of seven – it is time to protect yourself.

“Every time your skin is exposed to the sun, it is damaged by ultraviolet rays,” Dr Sarah Brewer, GP and medical director of Healthspan, told Yahoo UK.

“In the short term, excess sun kills skin cells and damages small blood vessels, leading to inflammation with redness, heat, pain and sometimes blisters.

“Dead cells peel after several days.

Read more: Heatwave health warning as temperatures soar to over 30C

“In severe cases, sunburn is accompanied by sunstroke with dehydration, headache, vomiting, fever and even collapse.”

Repeated sunburn can cause premature ageing and thinning of the skin, which may take on a yellow hue with exposed blood vessels.

In severe cases, skin cancer can develop.

“This effect is directly linked to total lifetime exposure to the sun, and degree of sunburn experienced, especially in childhood,” said Dr Brewer.

Babies and children should always be kept in the shade, particularly between 11am and 3pm when the sun is most intense.

They should also wear covered clothing, with at least SPF30 sunscreen on exposed areas.

Many adults are reluctant to seek the shade on their quest for a golden glow.

“Tanning is the body’s response to the sun and signifies that damage has occurred,” said Dr Brewer.

“If you choose to tan, limit sun exposure to 15 minutes on the first day and only increase gradually.

“Ideally, you should use sunscreen whenever you expect to be in the sun for more than 15 to 20 minutes.

“The development of a tan when wearing sunscreen suggests that, although you did not burn, enough UVB radiation reaches the skin to stimulate production of melanin; a natural sunscreen produced in response to UV damage.”

Although sunscreen is often critical for our skin’s health, it does block vitamin D production, making supplements all the more important.

Vitamin D is an essential nutrient that helps keep bones, muscles and teeth healthy.

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“Used properly, even a sunscreen with a sun protection factor of SPF8 reduces vitamin D production in the skin by 95%, while SPF15 reduces vitamin D3 production by 99%,” said Dr Brewer.

Vitamin D supplementation is recommended, however, the experts also stress the natural source has benefits.

“Although replacement with vitamin D supplementation by mouth is often recommended, it should not completely replace a minimum of time spent in the sun as absorption of vitamin D may vary across individuals,” Dr Veronique Bataille, consultant dermatologist at The Medical Chambers Kensington, told Yahoo UK.

Dr Brewer added: “The usual advice is therefore to obtain 10 to 15 minutes sun exposure to the face, arms, hands and/or back – without sunscreen – two or three times a week.”

Mushrooms, supplemented cereals and oily fish, like salmon, are good dietary sources of the vital vitamin.

Once the body has sufficient levels of vitamin D, it “switches off” production.

Summer holiday fashion concept - tanning woman wearing sun hat at the beach on a white sand shot from above
A golden tan means skin damage has occurred. (Getty Images)

Sunscreen: How much to apply, how often and what to look for

Dr Brewer recommends sunscreen be applied 15 to 30 minutes before exposure.

“Use liberally; it takes around 36g (six teaspoonfuls) to cover the entire adult body properly,” she said.

The NHS recommends two tablespoons for an adult body wearing a swimming costume.

The sunscreen’s label should advise how often to apply. As a rule of thumb, reapply every two hours and immediately after swimming, sweating or towel drying.

Remember, just because you cannot see the sun does not mean it is not wreaking damage.

“A cloudy sky doesn’t protect you from the sun’s rays as at least 30% to 40% of ultraviolet rays penetrate through cloud cover,” said Dr Brewer.

When buying sunscreen, looks for ones that offer UVA and UVB protection, as well as having a 5-star rating.

“Sunscreens are rated according to their sun burn protection factor (SPF), which shows how effective they are at filtering UVB rays, the ones that burn and are most associated with skin cancer,” said Dr Brewer.

“In theory, SPF 15 absorbs 93% of UVB rays, SPF30 absorbs 97% and SPF50 absorbs 98% if applied to the correct thickness and frequency.

“The British Association of Dermatologists recommend using an SPF of 30, which offers high protection.”

The SPF also gives an indication of how long the sunscreen will protect you for.

“SPF30 increases time before burning by 30 fold,” said Dr Brewer.

“If you would have burned after 10 minutes without sunscreen, using an SPF30 sunscreen means you will burn after 300 minutes, if used correctly.”

UVA rays cause premature ageing.

“UVA protection is a rated from one star to five stars; the more the better, use at least a 4-star cream,” said Dr Brewer.

“Sunscreens that offer both UVA and UVB protection are sometimes called ‘broad spectrum’.

“Ideally you want SPF30 plus UVA ratings of four to five stars.”

Note, most sunscreens expire after two to three years.