How to Select a Sunscreen | SPF, Labels, and the Rules That Matter

Choosing a sunscreen feels harder than it should be, with shelves full of numbers, claims, and formats. The good news is that the selection process comes down to three label checks that the FDA and dermatologists agree on. Getting the right one for your skin and your day starts with knowing what those terms actually promise, and what they don’t.

The Three Label Checks That Matter Most

The American Academy of Dermatology (AAD) keeps the selection process simple: look for a sunscreen that is broad spectrum, has an SPF of 30 or higher, and is water resistant. Those three traits cover the vast majority of sun exposure, whether you’re gardening for an hour or spending a full day at the lake.

Here’s what each term means on a U.S. label:

• SPF 30 or higher. SPF stands for sun protection factor, and the FDA describes it as the level of sunburn protection a product offers. SPF 15 filters about 93% of UVB rays, SPF 30 filters about 97%, and SPF 50 filters about 98%. Past a certain point, the gains get small, which is why SPF 30 is the standard recommendation for daily use.
• Broad spectrum. This label means the product protects against both UVA and UVB rays. The FDA’s test for this designation requires a mean critical wavelength of 370 nanometers or greater, which is a technical way of confirming the sunscreen covers the full ultraviolet range that damages skin.
• Water resistant. The FDA only allows a product to claim “water resistant (40 minutes)” or “water resistant (80 minutes)” if it passes a specific test. If a label doesn’t say this, plan to use a water-resistant product when you’re swimming or sweating.

Matching the Sunscreen to What You’re Doing

The best sunscreen depends on your day. For everyday indoor use, an SPF 30 product is generally plenty. But if you’re planning extended time outdoors—say, a long afternoon of weeding or a day at the beach—dermatologists recommend stepping up to SPF 50 or higher with water resistance.

For people concerned about dark spots or melasma, the AAD notes that a tinted sunscreen containing iron oxide offers better protection against the visible light that can worsen those patches. Tinted formulas are worth a look if this is a specific concern for you.

If you’re ready to compare finished products side by side, our tested roundup of cosmetic sunscreens that feel good on skin covers formulas that layer well under a full face of makeup.

Common Mistakes That Undo Good Sun Protection

Even a great bottle fails if it’s used wrong. The most frequent errors are choosing an SPF below 30, skipping the broad-spectrum check, trusting a waterproof claim, and forgetting to reapply after time in the water or a heavy sweat.

Reapplication matters more than most people think. The FDA is clear that sunscreen is not permanent, and every product is eventually washed off by water, sweat, or friction. The agency’s guidance directs consumers to follow the label instructions for when to reapply, and the AAD reinforces that reapplying is a required step, not an optional one.

There’s no such thing as waterproof sunscreen, and the FDA says so explicitly. If a label claims otherwise, it’s not an approved product. The honest rule is simple: water-resistant means it holds up for 40 or 80 minutes in the water, and then you reapply.

How Much to Apply and How to Make It Last

Most people under-apply sunscreen, which cuts protection dramatically. The general guidance is to use about one ounce—roughly enough to fill a shot glass—to cover all exposed skin on your body. That’s the benchmark dermatologists use, and it applies to lotions, creams, and sprays alike.

Skin protection doesn’t end with sunscreen. The FDA advises treating it as one part of a broader sun-safety routine that includes shade, protective clothing, hats, and sunglasses, especially during peak hours. Sunscreen fills the gaps that clothing and shade can’t cover, and vice versa.

If you’re spending the day outside, the workflow is straightforward: apply a generous layer 15 minutes before going out, use the water-resistant interval printed on the label as your timer, and reapply to any skin that’s still exposed. That sequence, repeated through the day, is the entire secret.