Is chemical sunscreen water resistant?

What should you look for on the label?

For swimming or sweaty outdoor activity, choose sunscreen with three separate features: SPF 30 or higher, broad spectrum protection against UVA and UVB rays, and water resistance. SPF describes sunburn protection, while water resistance describes protection during swimming or sweating. SPF and water resistance are separate label claims, so one large number cannot do all the paperwork.12

In the United States, a sunscreen labeled water resistant must pass testing and state whether it remains effective for 40 or 80 minutes of swimming or sweating. Those minutes describe water resistance, not permission to spend that long in the sun without other protection. For swimming, shop for a water resistance claim rather than a sporty name, because the pool does not read branding.1

Water resistance is not exclusive to chemical sunscreen. Mineral products can carry the claim too: Blue Lizard Australian Sunscreen Sport Mineral Spray has a Canadian licence listing zinc oxide as its medicinal ingredient and water and sweat resistance. Read the actual bottle for its duration and directions, especially when buying sunscreen from another country.13

How do you use it before swimming?

1. 1Apply sunscreen about 15 minutes before going outdoors. Do not wait until you are already in the sun to start applying it.
2. 2Use enough to cover every exposed area. Most adults need at least about 1 ounce, roughly a shot glass, for skin not covered by clothing; a larger body can need more.
3. 3Rub sunscreen thoroughly into the skin. Remember your ears, neck, hands, legs and tops of your feet, not just your face and shoulders.
4. 4Reapply every two hours outdoors and immediately after swimming or sweating. Follow the bottle's water resistance limit and reapplication directions rather than treating the two hour interval as the only rule.

Sunscreen can go into your morning routine, but that first application does not replace later reapplication. Using too little or forgetting to reapply can leave you sunburned. Water and light sand can also increase UV exposure, so a beach day needs more than a bottle with the right claim.4

Use shade, clothing, a hat and sunglasses alongside sunscreen. Cover as much skin as practical with lightweight shirts and pants, and choose sunglasses with UV protection. Apply sunscreen to exposed feet if you wear sandals. These measures matter for all skin tones, not only skin that burns quickly.5

What if sunscreen causes a rash?

Water resistance does not tell you whether a sunscreen suits sensitive skin. Sunscreen allergy can involve a UV filter, fragrance or preservative. If a product causes a rash, stop using it and ask a doctor about identifying the trigger. A dermatologist can use patch testing, and sometimes testing with light exposure, to investigate sunscreen reactions. Zinc oxide or titanium dioxide sunscreen may suit people allergic to chemical filters, but avoiding the specific ingredient responsible is what matters.6

If sunlight triggers a recurring rash, or you take medicine that increases sun sensitivity, water resistance alone is not enough to plan your protection. Photosensitivity means a condition caused or aggravated by sunlight. Managing it involves sun protection and treatment of the underlying problem; sunscreen alone often does not completely prevent these reactions.7