Chemical vs. Physical: Which Type of Sunscreen Is Best?
A Dermatologist's Advice on How to Sift Through a Sea of Labels in the Drugstore Aisle
Now with the approval of Mexoryl and Mexoryl SX, we have effective UVA blockers with photostability. These specific UVA blockers had to undergo an approval process at the FDA unlike one that had never been seen before in the cosmetic world.
Choosing sunscreen can be confusing. There are organic and inorganic types, and jargon like UV, SPF and broad-spectrum to sift through. Craig Burkhart, an associate professor of dermatology at the University of North Carolina at Chapel Hill, explains.
Chemical vs. Physical
Probably the most commonly used sunscreens are "chemical absorbers." They contain carbon compounds made in a laboratory. Some 22 chemicals have become available in the U.S. to shield the skin from the sun's harmful rays since the first compound PABA was developed in the 1940s.
Physical blockers come in two types: zinc oxide and titanium dioxide—natural minerals ground down to fine powders. These used to leave white residue on the skin but modern processing techniques have largely done away with that. "The benefit of physical blockers is that they don't decompose through sun exposure, so they theoretically have a longer life on your skin," Dr. Burkhart says. The downside: "They tend to feel greasy."
The Food and Drug Administration prefers manufacturers use the term organic when referring to chemical sunscreens—because they contain carbon compounds—and inorganic for physical sunblocks.
Rays of Light
The sun's radiation comes in three varieties when it reaches the Earth: UVB rays, primarily responsible for causing sunburn, and UVA1 and UVA2, which age the skin. "But [all three] contribute to the development of skin cancer," Dr. Burkhart says. Broad-spectrum sunscreens are meant to protect against a range of radiation wavelengths.
When sunlight hits the skin, chemical absorbers absorb the active UV rays and release their energy in harmless ways. When UV rays hit skin coated in physical blockers, they are reflected and cannot penetrate the skin. The FDA recommends using sunscreen with an SPF, or sun-protection factor, of at least 15.
Dr. Burkhart prefers physical blockers. Still, he says, the best sunblock is whatever people will use.
"Whether it's a chemical or a zinc oxide or titanium dioxide product, I want you to use broad-spectrum sunblock every time you go outside, and I want you to apply it every two hours while you're exposed to the sun," he says. Even though sunscreen is made to last under light for several hours, "the sunscreen can move around or fall into hair follicle pores or anywhere else," explains Dr. Burkhart, giving the body uneven coverage.
His preferred method: Start the day with a physical-block sun cream, then reapply it every two hours.
Still, he says: "If you put some SPF on, any at all, I'm happy."
Ignore the Lab Rat
Some people are concerned that sunscreens, especially chemical-based ones, can be absorbed through the skin and cause hormonal changes in people. "That came from a study where scientists had the mice bathe in the sunscreen daily and even eat it," Dr. Burkhart says. "I don't know of any proof of estrogen-like effects in humans."
The benefits of using any sunscreen far outweigh the outside risk of these effects, Dr. Burkhart says.
At least 20 published studies have also looked at whether physical blockers can pass through the skin into the body, he says, and shown that penetration of zinc oxide and titanium dioxide is negligible.
Another possible concern: Blocking the sun's rays could result in vitamin D deficiency. "There are other ways to get vitamin D—it's in milk, it's in cereal," he says.
A Few Exceptions
Dr. Burkhart advises against using any type of sunscreen on babies younger than 6 months. They should be kept out of the sun. And people with broken skin or rashes should talk to a doctor before applying sunscreen to those parts of their bodies.
Skin allergies are manageable. "If you have allergies to one of the chemical absorbers, there is usually another chemical you can change to. But I'd just turn to the inorganic blockers," he says. Often, it's the fragrance or preservatives that give people reactions, he says.
Email your Burning Questions to firstname.lastname@example.org