Sun Safety Basics: How to Choose SPF and When to Reapply Sunscreen

Short answer: Choose a broad-spectrum, water-resistant sunscreen with SPF 30 or higher, apply about 1 ounce (a shot glass full) to exposed skin 15 minutes before you go out, and reapply every two hours and right after swimming or sweating. [S01] [S02] [S03] Pair sunscreen with shade, protective clothing, a wide-brimmed hat and UV-blocking sunglasses, especially when the UV Index is 3 or higher. [S05]

Sunscreen only works as well as you use it. This guide covers what the label means, how much to use, when to reapply, and the other everyday habits that reduce sun exposure.

Know when protection matters most

UV rays are strongest from 10 a.m. to 4 p.m. daylight saving time in the continental US, according to CDC, and CDC advises protecting your skin when the UV Index is 3 or higher. [S05] The FDA's guidance is to limit time in the sun especially between 10 a.m. and 2 p.m. [S04]

Two easy checks:

• The UV Index. It appears in most weather apps. EPA's scale calls for sun protection from 3 upward, with more precautions as the number rises. [S06]
• The shadow rule. If your shadow is shorter than you are, UV exposure is higher. Seek shade and protect your skin and eyes. [S06]

What the UV Index numbers mean

EPA groups the UV Index into three bands: [S06]

How to choose a sunscreen

Read the three key label terms

The AAD recommends a sunscreen that says all three of these: [S01]

The FDA's baseline advice is a broad-spectrum sunscreen with SPF of at least 15. [S04] Dermatologists recommend going higher, to SPF 30. [S01]

What the SPF number does and does not mean

SPF mainly reflects protection from UVB rays. The FDA explains that SPF relates to the amount of sun exposure, not the time you can spend outside. [S04] The AAD notes that SPF 30 blocks about 97% of UVB rays; higher numbers block slightly more, but no sunscreen blocks 100%, and high-SPF products need reapplying just as often as lower ones. [S03]

Higher SPF can still be useful because most people apply too little. The AAD cites research finding people often apply only 20% to 50% of the amount needed to reach the SPF on the label. [S03]

Mineral or chemical?

Sunscreens with zinc oxide, titanium dioxide or both are called physical (mineral) sunscreens; those without either are chemical sunscreens, and hybrids contain both types of active ingredients. [S03] The AAD says any of them can protect you if it is broad spectrum, water resistant and SPF 30 or higher. People with sensitive skin may prefer mineral options. [S03]

If you are prone to dark spots, a tinted broad-spectrum sunscreen with iron oxide also helps protect against visible light. [S02]

Pick a form you will actually use

Sunscreen comes as lotions, creams, sticks, gels, oils, butters, pastes and sprays. [S04] Use spray sunscreen carefully: the FDA says never to spray it directly onto your face, and not to apply or wear spray sunscreen near open flames because it can be flammable. [S04] Spray into your hands first, then apply to the face.

How to apply sunscreen correctly

• Apply 15 minutes before going out, on dry skin. [S03]
• Use enough. Most adults need about 1 ounce, roughly a shot glass, to cover skin not covered by clothing. [S02] For the face, use at least 1 teaspoon, about enough to cover the length of your index and middle fingers. [S03]
• Cover the spots people miss: tops of the feet, neck, ears and the top of the head. [S03]
• Protect your lips with a lip balm that has SPF 30 or higher. [S02]

How often to reapply sunscreen

This is where most sun protection fails. The AAD says people who get sunburned usually did not reapply, used too little, or used expired sunscreen. [S02]

• Every two hours when you are outdoors. [S02]
• Immediately after swimming or sweating, even with water-resistant sunscreen. [S02]
• After toweling off, per CDC. [S05]

No sunscreen is waterproof or sweatproof; the FDA says all sunscreens eventually wash off. [S04] Makeup and moisturizers with SPF are convenient, but the AAD notes they still need reapplying about every two hours outdoors. [S03]

A practical tip for long days outside: set a two-hour phone timer when you first apply, and pack a travel-size bottle in your bag.

What changed on sunscreen ingredients in 2026

The FDA regulates sunscreens as over-the-counter drugs, and two updates this year affect the ingredient list on the label: [S04]

• A new permitted ingredient. In June 2026, the FDA added bemotrizinol as a permitted active ingredient in sunscreens, which it says should widen the choice of sun protection products.
• Two ingredients removed. On September 10, 2026, the FDA issued a final order removing aminobenzoic acid (PABA) and trolamine salicylate from the sunscreen monograph, after finding their risks outweigh their benefits. The FDA says consumers do not need to take any action, because it is not aware of any sunscreens currently sold that contain them.

To see which active ingredients a sunscreen uses, look at the section on the container labeled "Active Ingredients." [S03]

Store and replace sunscreen

• Check the date. The FDA says sunscreen without an expiration date should be considered expired three years after purchase, and expired sunscreen should be thrown away. If you do not know how old a bottle is, discard it. [S04]
• Keep it cool. Labels advise protecting the container from excessive heat and direct sun. [S04] In a hot car or on the beach, keep it in a bag or cooler.

Sun safety beyond sunscreen

Sunscreen is one layer. CDC recommends combining several: [S05]

• Shade, especially in the middle of the day.
• Clothing that covers your arms and legs. Tightly woven fabric protects best, and a wet T-shirt gives less protection than a dry one.
• A wide-brimmed hat that shades your face, ears and neck.
• Sunglasses that block both UVA and UVB rays.

For babies, the FDA advises asking a doctor before using sunscreen on infants under 6 months and keeping them out of the sun, with protective clothing if they must be outside. [S04]

A quick sun-safety checklist

Before you head out for more than a few minutes:

• Check the UV Index; plan shade and cover-up if it is 3 or higher. [S05]
• Pick a broad-spectrum, water-resistant sunscreen with SPF 30 or higher, and confirm it is not past its date. [S01] [S04]
• Apply about 1 ounce to exposed skin and at least 1 teaspoon to the face, 15 minutes before going out. [S02] [S03]
• Put on SPF 30+ lip balm, a wide-brimmed hat and UV-blocking sunglasses. [S02] [S05]
• Set a reminder to reapply in two hours, and reapply sooner after swimming, sweating or toweling off. [S02] [S05]
• Pack the sunscreen in a bag or cooler, out of direct sun. [S04]

Packing for appointments and travel

If you are traveling for care or supporting someone who is, sun exposure often comes from waiting outdoors, walking between buildings or long drives. Add sunscreen, a hat and sunglasses to your bag alongside the items on our extended-stay hotel checklist, and share the reminder with your support team using our caregiver travel planning guide. For the visit itself, see planning a cancer-center visit.