Ask any dermatologist what the best anti-aging treatment is, and you are guaranteed to get the same answer: sunscreen. If you are not already reaching for it regularly, you should be — slathering on sunscreen every day not only helps prevent skin cancer but is also the most effective (and least expensive) way to prevent premature aging.
Sometimes we forget that sunscreen’s function goes beyond just preventing sunburns. “The purpose of using a sunscreen is to reduce the risk of sun damage, including pre-cancerous lesions and skin cancers, but to also reduce signs of aging caused by the sun, including wrinkles, fine lines, blotchy skin, thinning skin, loss of collagen, loss of elastin, sun spots, redness and even sunburns,” says Kenneth Mark, M.D., board-certified cosmetic dermatologist and skin cancer expert in NYC.
Wearing sunscreen every day is a no-brainer, but debates over which type you should be using gets a bit more heated. And as confusion grows between “physical sunblocks” and “chemical sunscreens,” it is more important than ever for sun-soakers to understand the differences between the two.
Chemical Sunscreen vs. Physical Sunscreen: What Do They Do?
Chemical sunscreens are probably the most common form of sun protection on the market and are made up of different chemicals that absorb UV rays. This process “creates a chemical reaction, changing the UV rays into heat, [where that] heat is then released from the skin,” says Hadley King, M.D., a board-certified dermatologist in New York City. You can find a combination of two to six of these ingredients in every chemical sunscreen: oxybenzone, octinoxate, avobenzone, octisalate, octocrylene and homosalate.
Physical sunblocks, on the other hand, either contain the mineral ingredients zinc oxide and/or titanium dioxide, which “sit on top of the skin to scatter and deflect UV rays, physically blocking them from penetrating the skin,” says King.
Pros and Cons of Chemical Sunscreens
Many consumers love chemical sunscreen because of its lightweight texture and easy blend-ability, making it a perfect canvas for foundations and concealers. Since each chemical in a chemical sunscreen does not fully block the UVA and UVB spectrum in and of itself, there must be multiple chemicals cross-linked or stabilized in the formula so that it provides adequate protection and does not become useless upon sun exposure. “The physical blockers tend to not have this problem,” says Mark.
Pros and Cons of Physical Sunblocks
Sunblocks containing zinc oxide and/or titanium dioxide are photostable, meaning they do not change their molecular structure when exposed to UV radiation. “Zinc oxide offers the most thorough protection, while titanium dioxide is second best,” says King. “Unlike chemical sunscreens, [which require you to wait 20 minutes before sun exposure so your skin can fully absorb the product], physical sunblocks work as soon as you apply them, so you don’t need to wait.”
Unlike chemical sunscreens, physical sunblocks work as soon as you apply them, so you don’t need to wait.
Some folks fear that sunscreen will cause a breakout or inflammation on sensitive skin, but since physical sunblocks are less likely to clog pores and irritate complexions, they are ideal for those with acne-prone or sensitive skin. “Avobenzones, benzophenones, oxyphenones, methoxycinnamate and para-aminobenzoic acid (PABA) are all common chemical sunscreen ingredients that can cause pimples in sensitive, acne-prone skin,” says King. “Plus, chemical sunscreen ingredients are absorbed into the skin while mineral physical blockers sit on top of the skin, and I think that’s one reason why the chemical ingredients are more likely to cause reactions.” Although zinc oxide and titanium dioxide both will not clog pores, it is important to look for “non-comedogenic” on the product label.
Additionally, physical sunscreens are more stable than chemical ones, meaning they have a longer shelf life. “Expiration dates are stamped on sunscreen containers to specify the time limit for the product’s stability and efficacy,” explains King. “For optimal sun protection as well as texture, stability and sterility, use the sunscreen prior to the expiration date.”
Although physical sunblocks provide more broad-spectrum UVA and UVB protection than a chemical formula, the “white cast” that they leave is always the biggest complaint. Once an opaque, paste-like consistency, physical sunblocks have drastically developed over the years, with manufacturers creating more cosmetically elegant formulations by micronizing the particles. “Micronized zinc oxide and titanium dioxide can clump together over time, so the particles are coated with dimethicone or silica to keep the ingredients stable and smooth,” says King. Chemical sunscreens were once the king of the sunscreen shelves, but now that more brands are coming out with physical blocks that leave a little white residue, the shelf-balance is starting to shift.
The Aftermath of Chemical Sunscreens
Both King and Mark recommend wearing physical sunscreen. Chemical sunscreens provide sun protection, but they also might be destroying our stunning coral reefs, too. “Oxybenzone and octinoxate have been shown to have a negative impact on coral reefs, and in 2018, Hawaii became the first state to prohibit the sale and distribution of any sunscreens containing these ingredients,” says King. “These chemicals have been found to be highly toxic to juvenile corals and other marine life.”
Recent studies have shown that some chemical sunscreen ingredients may be potentially harmful as they can mimic hormones. “Oxybenzone has been linked to allergies, hormone disruption (estrogenic activity) and cell damage,” says King, “while avobenzone, upon exposure to sunlight, may become reactive and cause free-radical damage to DNA when absorbed.”
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