How to Choose Sunscreen | SPF, Label Rules, and the Right Fit

Picking a sunscreen shouldn’t feel like a chemistry exam, but a quick trip down the skin-care aisle shows shelves stacked with sprays, lotions, and sticks making all kinds of promises. The good news is that federal rules strip away most of the guesswork. The FDA regulates sunscreen labeling, so terms like “broad spectrum” and “water resistant” have precise, test-based meanings. You just need to know what to look for. This guide breaks down the three label features that matter, clears up the mistakes that lead to sunburn, and points you to a buying decision you won’t second-guess.

What Do the Label Terms Actually Mean?

Three phrases on the front of any sunscreen bottle carry real weight. Understanding them settles most of the decision before you even pick up a second product.

Broad spectrum means the formula shields you from both UVA and UVB rays. UVB rays burn, while UVA rays age the skin and contribute to skin cancer. A sunscreen labeled only “SPF 30” without the broad-spectrum claim blocks UVB but leaves you exposed to deeper-penetrating UVA. The FDA requires that a product pass a specific test before it can carry this label.

SPF, or sun protection factor, measures how well a sunscreen blocks UVB rays. The FDA holds that any product must offer at least SPF 15 to even make broad claims, while the American Academy of Dermatology (AAD) pushes that baseline higher. The AAD’s guidance is simple: choose an SPF of 30 or higher for everyday protection, which blocks about 97 percent of UVB rays.

Water resistant tells you how long the sunscreen stays effective while you’re swimming or sweating. Federal rules require the label to state the duration plainly: either 40 minutes or 80 minutes. No sunscreen is ever “waterproof” or “sweatproof”—the FDA bans those terms outright because every formula eventually washes off.

How Much SPF Do You Really Need?

SPF numbers climb fast, but your practical needs don’t rise at the same rate. SPF 30 filters roughly 97 percent of UVB rays. SPF 50 pushes that to about 98 percent, and SPF 100 reaches roughly 99 percent. That small difference matters less than how you apply the product.

Here is the selection logic that works:

• Choose SPF 30 or higher for everyday trips outside, per the AAD’s standing guidance.
• Confirm the label says “broad spectrum” so UVA and UVB are both covered.
• Pick a water-resistant formula if you’ll swim or sweat, and check whether it’s rated for 40 or 80 minutes.
• Skip any product below SPF 15 or without the broad-spectrum claim—the FDA limits what these can say about protection.

One common trap: treating a high SPF as a free pass to skip reapplication. A sunscreen labeled SPF 70 still fails you if it washes off. The FDA directs you to follow the product’s reapplication directions, and the AAD says to reapply after swimming or sweating. The real-world rule is to reapply roughly every two hours, or sooner if you’re in the water.

Common Sunscreen Mistakes to Avoid

Most sunburns come down to a few predictable errors rather than a bad product.

Trusting a “waterproof” label. That claim is illegal on U.S. sunscreen labels. If a product says it, put it back—the manufacturer is already ignoring the FDA’s rules.

Skipping sunscreen when it’s cloudy. The FDA’s guidance still recommends broad-spectrum sunscreen on overcast days. Up to 80 percent of UV rays can penetrate cloud cover.

Using a non-water-resistant formula for a swim. A regular lotion washes off in minutes. If you’re heading to the pool or planning a sweaty afternoon of yard work, the 40- or 80-minute rating is the feature you’re paying for.

Forgetting that water resistance is a timer, not a shield. That 80-minute rating means exactly that: after 80 minutes in the water, the protection drops. You reapply after that window passes, not at the end of the day.

Choosing a Formula That Fits Your Day

Once the label terms check out, the rest is about matching the product to the situation.

For a routine morning walk or a short commute, a broad-spectrum SPF 30 lotion does the job. For a beach day or a long bike ride, switch to a water-resistant formula and mind the 80-minute mark. If you’re buying for the whole family, look for a product everyone tolerates—a spray or stick often wins over a heavy lotion for kids.

For eco-conscious shoppers, our tested list of eco-friendly sunscreens covers reef-safe formulas that hold up under real outdoor use. Mineral options with zinc oxide are a solid place to start if you prefer a physical block over chemical filters, and the AAD notes that mineral formulas are a good choice for sensitive skin.

Here is a quick reference for the common scenarios:

Whichever formula you pick, apply it generously—most people use about a shot glass worth for their body—and reapply on schedule. The FDA notes that all sunscreens eventually wash off, and the AAD’s guidance is to reapply at least every two hours. A product you actually use correctly beats a perfect formula you forget about.