Researchers urge people to use higher-SPF products to compensate for tendency to apply protection too thinly.
The typical way most of us apply sunscreen leaves our skin with less than half the expected protection from damaging ultraviolet rays, say scientists.
New research has revealed that when sunscreen is applied in a typical way, it provides only 40% of the protection they might expect based on the sun protection factor (SPF). Most skin cancers are caused by DNA damage from UV radiation in sunlight.
The study found that protection of the skin from the harmful, UV-induced DNA damage known to underlie cancers was only significant when sunscreen was applied at a thickness between 1.3 and 2.0 milligrams per centimetre squared, whereas most people only apply a layer of 0.75.
Scientists suggest we could increase our protection by wearing a higher SPF to compensate for the tendency to apply sunscreen too thinly. “Given that most people don’t use sunscreens as tested by manufacturers, it’s better for people to use a much higher SPF than they think is necessary,” said study leader Antony Young, professor of experimental photobiology at King’s College London.
Quoted SPF ratings are based on the assumption that sunscreen is being applied at a thickness of 2 milligrams per centimetre squared, according to manufacturer’s recommendations, but the average sunscreen user typically applies much less, according to previous studies.
“People are typically getting much less protection than they think,” said Young. “For example, if you get SPF20 and use at a lower thickness of 0.75 milligrams per centimetre squared, your level of protection could be as low as SPF4.”
To investigate how protective sunscreen is when it is applied in a way that more closely resembles people’s day-to-day use, researchers measured the amount of DNA damage in the skin of 16 volunteers who were wearing different thicknesses of sunscreen when they were exposed to UV light.
The study participants were split into two groups of eight: one group received just a single dose of UV radiation to mimic sunlight exposure, and the second group received several doses over a period of five days to mimic continuous holiday exposure.
Volunteers received their UV radiation doses within 15 minutes of having their sunscreen applied, and skin biopsies were taken immediately after UV exposure. The sunscreen tested in the study, published in the journal Acta Dermato-Venereologica, was compliant with EU regulations.
The scientists also varied the amount of UV radiation during the experiment to try to replicate conditions in classic holiday destinations like Tenerife.
Skin biopsies revealed that those in the “holiday group” who wore sunscreen at the higher, manufacturer-recommended thickness also experienced the most significant protection from damage, even after being exposed to high doses of UV over several days, compared with those who wore a more typical, thin layer of sunscreen.
“There is no dispute that sunscreen provides important protection against the cancer-causing impact of the sun’s ultraviolet rays,” said Young. “However, what this research shows is that the way sunscreen is applied plays an important role in determining how effective it is.”
Nina Goad of the British Association of Dermatologists said: “This research demonstrates why it’s so important to choose an SPF of 30 or more. In theory, an SPF of 15 should be sufficient, but we know that in real-world situations, we need the additional protection offered by a higher SPF.
“An extra consideration is that when we apply sunscreen we are prone to missing patches of skin, as well as applying it too thinly.”
She added that people should not rely on sunscreen alone for sun protection, but should also use clothing and shade.