A Mercadona scientist debunks the myth about the protection duration of sunscreen.

Sunscreen should be used year-round, especially on the face, although it's best to use them most frequently during the summer months to protect against the sun's ultraviolet radiation, which accelerates skin aging and can cause skin cancer. There are many myths and beliefs surrounding sun protection factors (SPF), which are indicated on packaging with numbers such as 15, 30, or 50, the latter being the most protective. Pilar Vinardell , a member of Mercadona 's Scientific Committee, has clarified in a video some of the doubts that often arise regarding the duration of creams with SPF 50.

"If we apply SPF 50 sunscreen just once a day , will we be protected? " is the question posed by Vinardell, a professor of Physiology at the Faculty of Pharmacy and Food Sciences at the University of Barcelona and an expert in cosmetic safety assessment.

"This is a myth ," he responds. "Although SPF 50 blocks 98% of ultraviolet B (UVB) radiation, which is responsible for sunburns and most skin cancers, its effect only lasts two hours," he explains.

Over time, he continues, " sweat, water, friction with clothing or sand" degrade the high protection indicated on the cream's packaging.

"A SPF of 50 protects you more intensely, but not for longer ," clarified this expert from the Valencian supermarket chain.

According to Pilar Vinardell, "the key to adequate protection is repeated application in sufficient quantities ."

At this point, dermatologists recommend following the two-finger rule for face cream and around two tablespoons or a shot glass (30 ml) for the rest of the skin on your body that will be exposed to the sun.

Dermatologist Ana Molina also recommends that products not only provide protection against ultraviolet B rays, but also "have the word PA or UVA surrounded by a small circle , which means that it also protects against ultraviolet A," in addition to protection against infrared rays and visible light, that is, that it be "broad spectrum," she explained in a recent interview on Telemadrid.

For those concerned about not getting enough vitamin D from the sun, Molina says, " You're still going to make vitamin D even if you wear sunscreen."