{"id":60003,"date":"2025-08-12T12:48:00","date_gmt":"2025-08-12T12:48:00","guid":{"rendered":"https:\/\/gulftimes.ae\/how-does-sunscreen-work-and-what-do-spf-and-star-ratings-mean\/"},"modified":"2025-08-12T12:48:00","modified_gmt":"2025-08-12T12:48:00","slug":"how-does-sunscreen-work-and-what-do-spf-and-star-ratings-mean","status":"publish","type":"post","link":"https:\/\/gulftimes.ae\/?p=60003","title":{"rendered":"How does sunscreen work, and what do SPF and star ratings mean?"},"content":{"rendered":"
Temperatures are set to be well above average in many parts of the UK, and UV levels are expected to be high. <\/p>\n
How can you protect your skin from the sun’s rays and what should you do if you get burned? <\/p>\n<\/div>\n
What do the SPF numbers mean on sunscreen?<\/h2>\n<\/p>\n
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The most prominent number on sunscreen bottles is the sun protection factor or SPF.<\/p>\n
The higher the number, the greater the protection it offers.<\/p>\n
SPF tells you how much protection your sunscreen provides from UVB radiation. The number refers to how much UVB it allows in, not how much it blocks.<\/p>\n
For example, a sunscreen with SPF 15 allows one-fifteenth of the sun’s rays to reach your skin, or about 7%.<\/p>\n
So it filters out about 93% percent of UVB rays while SPF 30 filters about 97%.<\/p>\n
This means if you could stay in the sun for 10 minutes unprotected without burning, SPF 15 would in theory give you 15 times that protection, or two-and-a-half hours before you would burn.<\/p>\n<\/div>\n\n
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The British Association of Dermatologists says sunscreen with SPF 30 is a “satisfactory form of sun protection in addition to protective shade and clothing”.<\/p>\n
It says sunscreen should be reapplied at least every two hours, regardless of its SPF.<\/p>\n<\/div>\n
What are UVA and UVB and what do the star ratings mean?<\/h2>\n<\/p>\n
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Many brands also carry a star rating from one to five.<\/p>\n
This tells you the percentage of UVA radiation that is absorbed by the sunscreen in comparison to how much UVB is absorbed. The more stars the better.<\/p>\n
UVA and UVB refer to different wavelengths of radiation from the sun that enter the Earth’s atmosphere.<\/p>\n
UVA<\/b> is associated with ageing of the skin and pigmentation as well as skin cancer. It can affect human skin even through glass.<\/p>\n
UVB<\/b> causes sunburn, and is linked to particular types of skin cancer – basal cell carcinoma (the most common type) and malignant melanoma.<\/p>\n
A low SPF sunscreen could have a high star rating if the ratio of UVA to UVB protection is the same as in a higher SPF product.<\/p>\n
Ideally, you want a sunscreen with a high SPF and a high star rating.<\/p>\n<\/div>\n
How effective is the best sunscreen?<\/h2>\n<\/p>\n
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These levels of protection assume sunscreen has been applied in ideal conditions.<\/p>\n
In reality, most people do not apply sunscreen perfectly, and it can rub off with sweat or while in water. <\/p>\n
Experts think most people only apply half the recommended quantity.<\/p>\n
You should not use sunscreen which is past its expiry date as it may be less effective.<\/p>\n<\/div>\n\n
EU guidance states that sunscreen should only be marketed as having sun protection of “50+” and not the ratings of 80 or 100 which can be found in some countries.<\/p>\n
It thinks these could be misleading about how much extra protection they provide: SPF 50 provides about 98% protection, while SPF 100 would provide less than 100%.<\/p>\n
No product provides 100% protection from the sun’s rays so the advice is that everyone should cover up and seek shade when the sun is strongest.<\/p>\n<\/div>\n
What about ‘once-a-day’ sunscreens?<\/h2>\n<\/p>\n
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There are lots of “extended wear” sunscreens on the market that advertise themselves as being for use “once a day”. Many claim to offer protection for up to eight hours – if applied correctly.<\/p>\n
But some dermatologists recommend that these products should still be applied at least every two hours, like any other sunscreen, since the risk that you may have missed a spot – or that it will rub or wash off in that time – are too high.<\/p>\n
A Which? report in 2016 criticised four of these products for not providing the protection promised. It found that after six to eight hours, the average protection offered decreased by 74%.<\/p>\n
But this claim was rejected by some of the manufacturers, who said their own testing had produced different results.<\/p>\n<\/div>\n
What should you do if you get sunburned?<\/h2>\n<\/p>\n
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Sunburn results in hot and sore skin which may peel after a few days. In extreme cases, skin can blister.<\/p>\n
It usually gets better within a week or so, but there are things you can do to ease the symptoms.<\/p>\n
The NHS recommends getting out of the sun as soon as possible, and keeping burned skin covered to protect it from the sun until it has fully healed.<\/p>\n
A cool shower or a damp towel can help, as can moisturising aftersun products, painkillers and drinking plenty of water. Ask your pharmacist for advice.<\/p>\n
You should not put petroleum jelly or ice on sunburned skin. You should resist scratching the burned areas and avoid tight-fitting clothes.<\/p>\n
Contact your GP or NHS 111 if your skin is blistered or swollen or you have other symptoms of heat exhaustion or heatstroke.<\/p>\n
Regularly getting sunburned can increase the risk of skin cancer.<\/p>\n<\/div>\n<\/div>\n
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