Sunscreen Science: How Sun Protection Really Works and What to Watch For
When you put on sunscreen, a topical product designed to absorb or reflect ultraviolet radiation to prevent skin damage. Also known as sunblock, it’s not just a summer accessory—it’s one of the most effective tools we have to prevent skin cancer and premature aging. But not all sunscreens are created equal. The science behind them is more complex than just picking the highest SPF number on the shelf.
UV radiation, invisible rays from the sun that damage skin cells and trigger DNA mutations comes in two main types: UVA and UVB. UVB causes sunburns and is the main driver of skin cancer, while UVA penetrates deeper, breaking down collagen and causing wrinkles. Effective sunscreen must block both. That’s where SPF, Sun Protection Factor, a measure of how well a product protects against UVB rays comes in. SPF 30 blocks about 97% of UVB rays. SPF 50 blocks 98%. Going higher gives you almost no extra protection—and can trick you into staying in the sun too long.
Then there’s the sunscreen ingredients, the active compounds that either absorb UV light (chemical filters) or reflect it (mineral blockers). Zinc oxide and titanium dioxide are mineral filters. They sit on top of the skin, bounce UV away, and are less likely to irritate sensitive skin. Chemical filters like avobenzone and octinoxate absorb UV and convert it to heat. Some of these chemicals have raised concerns about skin absorption and environmental harm, especially to coral reefs. The FDA has only recognized zinc oxide and titanium dioxide as generally safe and effective. The rest are still under review.
Water resistance matters too. No sunscreen is truly waterproof. Labels that say "water resistant" mean it stays effective for 40 or 80 minutes while swimming or sweating. You still need to reapply. And don’t forget: sunscreen wears off. Rubbing, towel-drying, and even just sitting in the sun break it down. Most people apply only 25-50% of the amount used in lab tests. That means you’re getting far less protection than the bottle claims.
Here’s what most people miss: sunscreen alone isn’t enough. Hats, sunglasses, and shade are just as important. UV rays bounce off sand, water, and concrete. Even on cloudy days, up to 80% of UV radiation gets through. And yes—dark skin needs protection too. While melanin offers some natural defense, skin cancer in people of color is often diagnosed later, when it’s more dangerous.
The real question isn’t just "which sunscreen should I buy?" It’s "how am I using it?" Are you applying enough? Are you reapplying? Are you covering your ears, neck, and the tops of your feet? Are you checking the expiration date? Sunscreen expires. Heat and sunlight degrade the active ingredients. A bottle left in a hot car is useless.
This collection of articles dives into the real-world side of sunscreen science—not just how it works, but how it fails, how it’s misused, and what you can do to actually protect yourself. You’ll find guides on spotting misleading labels, understanding ingredient safety, dealing with sunscreen shortages, and even how certain medications make your skin more sensitive to the sun. These aren’t theoretical tips. They’re lessons from people who’ve learned the hard way.
Sunscreen Science: SPF, UVA/UVB, and Daily Protection Explained
Nov, 12 2025