Amidst the heatwave and holiday season, interest in sunscreens has surged to record levels. However, many remain unaware of the significance of the numbers on sunscreen packaging. It is a common misconception that a higher number implies stronger protection. In reality, the SPF number primarily indicates the duration of the protection rather than its strength.

The SPF number indicates how much longer you can stay in the sun without getting sunburned compared to not using any SPF. Dermatologist and skin cancer specialist Dr Ross Perry explained this on metro.co.uk.

"If you would burn after 15 minutes in the sun without protection, an SPF 30 would give you 30 times that protection – so around four to five hours in the sun without burning. SPF 100 generally just means that it would give 100 times the protection of what a normal burn time would be," Dr Perry explains to Metro.co.uk.

Determining the duration of unprotected sun exposure needed to cause sunburn is difficult. "Everyone is individual; one person may burn after 10 minutes while another may burn after 20 minutes, so one person may need to reapply after two hours while another needs to reapply after three," notes consultant dermatologist Dr Mary Sommerlad.

As metro.co.uk notes, human error is a big player in suncream effectiveness. "It is never the case that coverage will last exactly 100, 50 or 30 times the burn times as people sweat, wash SPF off in pools or the sea, or rub it off against clothing," says Dr Perry. Such things obviously reduce the effectiveness of sunscreen.

Studies have confirmed the efficacy of SPF 100 compared to lower SPF levels. For instance, a 2018 study involving 200 participants applying either SPF 50 or SPF 100 before six hours of sun exposure found that 55% of those using SPF 50 showed signs of sunburn, compared to only five per cent of SPF 100 users.

Dermatologists explain that there is minimal difference in the effectiveness of the filters in blocking UVB radiation. This radiation can penetrate the uppermost layers of the skin, causing burning, peeling, and blistering.

"SPF 100 is normally about 99% efficacious in terms of its sunblock, whereas SPF 50 is 98% and SPF 30 is 97%," Dr Perry explains. "As you can see, there is not a great deal of difference between them."

On the other hand, Dr Mary Sommerlad stresses: "Very pragmatically, SPF 100 lets in less UVB than traditional SPFs, so if you are prone to burning, the more protection, the better. However, 1% of UVB still will get through, and in intense sunlight, this can still be enough to lead to sun damage to the skin."

SPF 100 does not guarantee total sun protection. Given its relative scarcity compared to lower SPFs like 50 or 30, Dr. Perry recommends opting for a lower SPF and being meticulous about reapplication. Regular top-ups are also easier with lower SPF sunscreens, as SPF 100 formulas tend to be thicker and stickier to be slightly more effective.

Source: metro.co.uk