Choosing a sunscreen comes down to four things on the label: SPF number, broad spectrum protection, the type of active ingredient, and whether it’s water resistant. Get those right for your skin type and activities, and you’re covered. Here’s how to evaluate each one.
What SPF Numbers Actually Mean
SPF measures how much UVB radiation (the kind that causes sunburn) a sunscreen blocks. The numbers sound like they scale dramatically, but the actual protection differences are small once you get past SPF 30. SPF 15 blocks 93% of UVB rays, SPF 30 blocks 97%, SPF 50 blocks 98%, and SPF 100 stops 99%. The jump from SPF 30 to SPF 50 is just one percentage point of additional protection.
SPF 30 is the sweet spot for most people. It blocks nearly all UVB radiation and is widely available in every formula type. SPF 50 offers a small additional margin that can matter if you burn easily, spend long stretches outdoors, or tend to apply sunscreen too thinly (which most people do). Going above SPF 50 provides almost no measurable benefit and can create a false sense of security that leads you to skip reapplication.
Why “Broad Spectrum” Is Non-Negotiable
SPF only measures protection against UVB rays. UVA rays penetrate deeper into the skin, accelerate aging, and contribute to skin cancer risk. A sunscreen labeled “broad spectrum” has been tested to confirm it filters both UVB and UVA radiation. In the U.S., the FDA requires broad spectrum products to meet a specific threshold of UVA coverage based on lab testing. The European Union goes further, requiring that UVA protection reach at least one-third of the labeled SPF value.
If a sunscreen bottle doesn’t say “broad spectrum” on the front label, it may only protect against sunburn while leaving your skin exposed to UVA damage. Always check for those two words regardless of SPF number.
Mineral vs. Chemical Sunscreen
Sunscreens fall into two categories based on their active ingredients, and this is often the biggest decision point.
Mineral sunscreens use zinc oxide, titanium dioxide, or both. These sit on top of your skin and physically reflect UV light away. They start working immediately on application. The FDA currently recognizes only these two ingredients as Generally Recognized as Safe and Effective (GRASE), which is the agency’s highest safety designation for over-the-counter ingredients. Mineral formulas tend to be gentler, making them a good default for sensitive skin, children, and anyone who wants the simplest option.
Chemical sunscreens use ingredients like oxybenzone, octinoxate, homosalate, avobenzone, and octocrylene. These absorb into the skin and work by converting UV rays into heat. They tend to blend more easily and feel lighter, which is why many people prefer them for daily wear under makeup. The tradeoff is that some chemical filters raise environmental and safety questions. The FDA has requested more data on these ingredients before classifying them as GRASE, though they remain legal and widely sold.
The old complaint about mineral sunscreens leaving a chalky white cast has largely been solved by newer formulations. Tinted mineral sunscreens, fluid-textured options, and micronized zinc oxide blends now go on smoothly across a range of skin tones.
Choosing by Skin Type
Oily or Acne-Prone Skin
Look for three phrases on the label: oil-free, non-comedogenic (won’t clog pores), and matte finish. Gel-based, water-based, or fluid sunscreens absorb quickly without adding shine. Mineral sunscreens with zinc oxide can actually help absorb excess oil throughout the day. Avoid heavy, cream-based formulas and anything with added fragrance, which can trigger breakouts. Some sunscreens designed for acne-prone skin also include niacinamide, a form of vitamin B3 that helps with blemishes and discoloration.
Dry or Sensitive Skin
Sunscreens formulated as moisturizers can pull double duty. Look for added hydrating ingredients like hyaluronic acid or ceramides, which help the skin retain moisture. Mineral formulas with zinc oxide are typically the least irritating option for reactive skin. Avoid products with alcohol high on the ingredient list, as they can dry out already parched skin.
Darker Skin Tones
All skin tones benefit from sunscreen, but the white cast from mineral formulas can be especially visible on medium to deep skin. Tinted mineral sunscreens solve this by blending a sheer color into the formula. Chemical and chemical-mineral hybrid sunscreens also tend to go on clear. If you prefer a pure mineral formula without tint, look for ones labeled “sheer” or “invisible” that use micronized particles.
Water Resistance Ratings
No sunscreen is waterproof. The FDA banned that term from labels years ago. What you’ll see instead is “water resistant” followed by either 40 minutes or 80 minutes. That number tells you how long the sunscreen maintains its labeled SPF while you’re swimming or sweating, based on standardized testing.
If you’re going to the beach, a pool, or exercising outdoors, choose an 80-minute water-resistant formula. Reapply as soon as you towel off or when the time window runs out, whichever comes first. For everyday commuting or errands, water resistance is less critical.
How Much to Apply
Most people use far too little sunscreen, which dramatically cuts the actual protection they get. The standard lab testing that determines SPF uses a thick, specific dose. In practice, a useful guideline is the “two-finger rule”: squeeze a line of sunscreen along both your index and middle fingers, from the base of the palm to the fingertips. That amount covers roughly one body zone, like your face and neck, or one arm.
For your entire body in a swimsuit, you’ll need about an ounce total, roughly the volume of a shot glass. If that feels like a lot, you’re probably not using enough day to day. Applying half the tested amount doesn’t give you half the SPF. It drops protection much more steeply than that. The most practical approach is to apply a generous layer, then reapply within 30 minutes to catch spots you missed. After that, reapply every two hours or after swimming, sweating, or toweling off.
Reef and Environmental Impact
Oxybenzone, octinoxate, and avobenzone have been linked to coral reef damage. When these chemicals wash off your skin in ocean water, they can harm reef health even in small concentrations. Hawaii, the U.S. Virgin Islands, Key West, and Palau have banned sunscreens containing oxybenzone and octinoxate. If you’re swimming in the ocean, choosing a mineral sunscreen with only zinc oxide or titanium dioxide avoids the most problematic ingredients. Look for labels that say “reef safe” or “reef friendly,” but verify the ingredient list yourself since those terms aren’t regulated.
Checking Expiration and Storage
Sunscreen degrades over time. FDA regulations require products to carry an expiration date unless the manufacturer has proven the formula stays stable for at least three years. If your sunscreen has no printed expiration date, treat it as expired three years after you bought it. If you can’t remember when you bought it, throw it out.
Heat and direct sunlight accelerate breakdown. Leaving a bottle on your dashboard or baking on a towel at the beach can degrade the active ingredients before the expiration date. Wrap containers in a towel or keep them in a cooler or shaded bag when you’re outdoors for long stretches. Sunscreen that has changed color, separated, or developed an off smell should be discarded regardless of date.
A Quick Label Checklist
- SPF 30 or higher: covers nearly all UVB radiation with a good margin for imperfect application
- Broad spectrum: confirms UVA protection, not just sunburn prevention
- Active ingredients you’re comfortable with: zinc oxide and titanium dioxide for the most established safety profile, or chemical filters if you prefer the texture
- Water resistant (40 or 80 min): necessary for swimming, sports, or heavy sweating
- Skin-type match: oil-free and matte for oily skin, hydrating formulas with ceramides or hyaluronic acid for dry skin
- Valid expiration date: or purchased within the last three years