Why this is the one that matters
If you do one thing for your skin, do this.
UV is the main cause of collagen breakdown, wrinkles, dark spots, and skin cancer. It's responsible for the large majority of visible skin aging.
The proof is on your own body. Compare the skin on your face or the backs of your hands to the skin on your buttocks or inner upper arm. Same age, same genes, completely different condition. The only variable is sun exposure.
Every other product in your routine is trying to repair damage. Sunscreen prevents it. That's a fundamentally better deal — and it's the one people skip.
What the numbers mean
SPF measures protection against UVB — the rays that burn.
- SPF 15 blocks about 93%
- SPF 30 blocks about 97%
- SPF 50 blocks about 98%
- SPF 100 blocks about 99%
Note how the gains flatten. SPF 100 is not three times better than SPF 30. SPF 30 is the sensible floor; SPF 50 is a reasonable default. Chasing higher numbers gives you diminishing returns and can create false confidence.
"Broad spectrum" means it also protects against UVA — and this matters more than the SPF number for aging.
UVA penetrates deeper, doesn't burn you (so you don't notice it), passes straight through window glass and clouds, and is the main driver of collagen loss and pigment. A high SPF without broad-spectrum protection leaves you exposed to exactly the rays that age you.
Always choose broad spectrum. In practice this is more important than whether you pick SPF 30 or 50.
Mineral vs. chemical
Mineral (physical) — zinc oxide, titanium dioxide.
Sits on the skin's surface and reflects and scatters UV. Works immediately. Very well tolerated — the right choice for sensitive skin, rosacea, eczema, babies, and post-procedure skin. Zinc oxide alone gives excellent broad-spectrum coverage.
The downside is cosmetic: mineral sunscreens can leave a white cast, which is a real and frequently dismissed problem for people with medium and darker skin. Modern tinted formulas largely solve it — and if a white cast is why you don't wear sunscreen, then finding a tinted one you like is the single most useful thing you can do.
Chemical — avobenzone, octinoxate, oxybenzone, and newer filters.
Absorbs UV and converts it to heat. Lighter texture, no white cast, blends invisibly. Cosmetically superior for most people.
Can sting sensitive skin or eyes. Needs about 15–20 minutes before sun exposure.
Which is better? The one you'll actually wear every day. This isn't a dodge — the best sunscreen in the world does nothing in the bottle. A chemical sunscreen you enjoy applying beats a mineral one you avoid.
A note on "chemical sunscreens are dangerous." Some filters are absorbed into the bloodstream, which prompted headlines. Absorption is not the same as harm, and no evidence shows these filters cause harm at the levels used. The FDA has asked for more data — that's ordinary regulatory diligence, not a warning. Meanwhile the risk of UV exposure is thoroughly proven. If you'd rather avoid them, use mineral. But don't skip sunscreen over this.
Tinted sunscreen — an underrated upgrade
If you have melasma or hyperpigmentation, this is worth knowing.
Visible light — not just UV — worsens melasma. Standard sunscreens don't block it at all.
Tinted sunscreens contain iron oxides, which do block visible light. For melasma, a tinted mineral sunscreen is meaningfully better than an untinted one, and dermatologists recommend it specifically for this reason.
It also solves the white cast problem. Two wins.
How to actually use it
Use enough. This is where nearly everyone fails.
The SPF on the bottle is measured using 2mg per square centimetre — far more than people apply. Most people use a quarter to half of what's needed, which means an SPF 50 applied thinly may be performing like an SPF 10.
For the face: about 1/4 teaspoon, or the two-finger rule — a line of sunscreen along the length of your index and middle fingers.
Don't forget: ears, neck, the back of your neck, your hands, and your eyelids. Hands and neck are where age shows most, and they're the most commonly missed.
Reapply every 2 hours in direct sun, and after swimming or sweating. For a normal indoor day, morning application is reasonable — but reapply if you're near windows for hours or go outside.
Wear it every day. Cloudy days: UVA passes through cloud. Winter: UVA is present year-round. Indoors near a window: UVA passes through glass. In the car: side windows don't block UVA.
Makeup with SPF doesn't count. You'd need to apply an implausible amount to reach the stated protection. Use it as a bonus, not as your sunscreen.
Beyond sunscreen
Sunscreen is one layer of defense, not the only one.
Shade, especially between 10am and 4pm.
A wide-brimmed hat — more reliable than reapplying sunscreen.
UPF clothing — doesn't wear off, doesn't need reapplying.
Sunglasses — eyelid skin is thin, and eyelid skin cancers are easy to miss.
FAQ
What SPF do I need?
SPF 30 minimum, broad spectrum. SPF 50 is a good default. Above that, gains are marginal.
Mineral or chemical?
Whichever you'll wear daily. Mineral for sensitive skin, rosacea, eczema, or after procedures. Chemical for a lighter feel and no white cast. Both work.
Are chemical sunscreens safe?
Yes, based on current evidence. Some filters are absorbed into the bloodstream, but absorption isn't harm, and no evidence of harm has been shown. The risks of UV exposure are, by contrast, well established. If you're concerned, use mineral — but wear something.
Do I need it indoors?
If you're near windows, yes. UVA passes through glass and it's the wavelength that ages skin. If you're in a windowless room all day, it matters less.
Do I need it on cloudy days?
Yes. UVA passes through cloud cover.
Does darker skin need sunscreen?
Yes. More melanin gives some natural protection — roughly equivalent to SPF 13 at most — which is nowhere near enough. And darker skin is more prone to hyperpigmentation, which UV directly worsens. Skin cancer in darker skin is also diagnosed later and has worse outcomes. Find a formula without a white cast — tinted mineral or a modern chemical one.
How much should I use?
About 1/4 teaspoon for your face. Or the two-finger rule. Almost everyone under-applies, which is why real-world protection falls far short of the number on the bottle.
Does my SPF moisturizer or foundation count?
Not really. You'd have to apply far more than anyone does. Use a dedicated sunscreen.
Which sunscreen is best for melasma?
A tinted mineral sunscreen with iron oxides. It blocks visible light, which worsens melasma and which ordinary sunscreens don't stop. This is a genuinely meaningful upgrade if you have melasma.