Um, no. “Yes, you can make your own sunscreen, but no, you should not do it,” says cosmetic chemist Perry Romanowski. “You can make your own car, too, but sometimes there are things you just shouldn’t do. Making your own sunscreen is a terrible idea.”
According to Perry, the Smiths are essentially making a body butter with some zinc in it, a far cry from real sunscreen. “It’s perfectly fine for people to make their own moisturisers because if you make it wrong, that’s not dangerous,” he says. “But if you make sunscreen wrong, you’re going to get burned.”
The couple’s DIY sunscreen wouldn’t provide any defence against burns, skin cancer, premature ageing, or any of the other risks that come with unprotected sun exposure. And there are a few key reasons why.
The first is the way their ingredients are combined. Zinc does provide sun protection (it is, after all, the key ingredient in many sunscreens), however, Perry says that their whisking method doesn’t properly distribute it. That causes an uneven spread of zinc, which would lead to “pockets” or “spots” of sunburn later on.
“When it’s professionally done, the zinc oxide is spread out into an even film,” he explains. “Additionally, formulators put polymers in [sunscreen] so when it’s spread on skin, it’s spread evenly.”
According to cosmetic chemist Kelly Dobos, chemists and formulators work hard to ensure sunscreen provides an even layer of active ingredients on the skin by using specialised equipment like homogenisers, ensuring that each formulation has an even particle size. “The particles want to stick together, so we want to break them and make sure they’re the right size to protect you,” she explains.
And while the Smiths’ sprinkle of zinc may look generous, it probably isn’t doing much to protect against the sun’s rays anyway. “Generally speaking, for every percentage of zinc oxide, you might get one or maybe two SPF,” Kelly says. (Dermatologists generally recommend a minimum of SPF30 for daily sun protection.)
Stability is also a factor, says Mona Gohara, MD, a board-certified dermatologist and associate clinical professor of dermatology at Yale. “[These homemade ingredients] may be stable together, but may not be stable when they hit the light,” she explains. “The preservatives and stabilisers that go into [professionally formulated sunscreens] that make them efficacious aren’t being considered.”