What SPF, broad spectrum, and water resistance mean, how much sunscreen to apply, and what the FDA says about ingredient safety.
A sunscreen label carries 3 claims that matter: the SPF number, the words broad spectrum, and a water resistance time. Each is defined by Food and Drug Administration (FDA) testing rules, so the terms mean the same thing on every bottle sold in the United States.
SPF stands for sun protection factor. It rates how well a product protects against sunburn, which is caused mostly by ultraviolet B (UVB) rays. The American Academy of Dermatology (AAD) recommends SPF 30 or higher, which blocks about 97% of UVB rays.
Higher numbers block slightly more, and no sunscreen blocks everything. A higher SPF does not last longer on the skin.
SPF says nothing about ultraviolet A (UVA), the longer rays that reach deeper into the skin and also contribute to skin cancer. Only products that pass a separate FDA test for UVA coverage may print broad spectrum on the label. Dermatologists advise choosing a product that has both SPF 30 or higher and the broad spectrum claim.
The FDA does not allow the words waterproof or sweatproof, because every sunscreen eventually washes off. A product can be labeled water resistant only if it states how long the SPF holds up during swimming or sweating: either 40 minutes or 80 minutes. After that time, or after towel drying, the skin needs a fresh coat.
Most people apply far too little. The AAD figure for an adult is about 1 ounce, enough to fill a shot glass, to cover the exposed skin of the body.
For babies under 6 months, the FDA and the AAD advise shade and clothing in place of sunscreen.
Sunscreen active ingredients fall into 2 groups. Mineral filters, zinc oxide and titanium dioxide, are fine particles that sit on the skin surface. Chemical filters, such as avobenzone, octocrylene, homosalate, and oxybenzone, are carbon-based molecules that absorb UV energy. Both groups work when applied properly. Dermatologists often suggest mineral products for sensitive skin because they are less likely to sting or irritate.
In June 2026 the FDA added bemotrizinol to the list of permitted filters, at concentrations up to 6%, for adults and children 6 months and older. The agency described this as the first new sunscreen active ingredient in the United States in about 20 years. Bemotrizinol covers both UVA and UVB.
The FDA has been updating its sunscreen rules for several years. In its proposed order, the agency classified zinc oxide and titanium dioxide as GRASE, short for generally recognized as safe and effective, at concentrations up to 25%. For 12 other filters, including avobenzone, oxybenzone, octocrylene, homosalate, octisalate, and octinoxate, the FDA asked manufacturers for more safety data. The agency has stated plainly that asking for data does not mean these ingredients are unsafe.
In September 2026 the FDA issued a final order removing aminobenzoic acid (PABA) and trolamine salicylate from the permitted list, after concluding that their risks outweigh their benefits. The agency knew of no sunscreens sold in the United States that still contain them.
Much of the public concern traces to 2 FDA-run studies led by Matta and colleagues. The first (JAMA, 2019) enrolled 24 healthy volunteers, and the second (JAMA, 2020) enrolled 48. Volunteers applied sunscreen to 75% of the body 4 times a day, the maximum use the label allows. Blood tests showed that all of the chemical filters tested reached levels above 0.5 nanograms per milliliter, some after a single application.
That threshold is a regulatory trigger. Above it, the FDA expects a manufacturer to run further toxicology studies, including tests for cancer and reproductive effects. The studies did not measure harm, and none was reported beyond occasional rash. Both papers end with the same sentence: the results do not indicate that people should refrain from using sunscreen. More data is needed on what, if anything, these blood levels mean for health. People who prefer to avoid the question can choose a mineral product.
Sprays make it hard to judge how much lands on the skin. The AAD advises spraying until the skin glistens and then rubbing the product in. Avoid breathing the mist, and never spray near an open flame or while smoking, because many sprays are flammable.
The FDA requires sunscreens to keep their original strength for at least 3 years. A bottle with no printed expiration date should be treated as expired 3 years after purchase. Heat breaks the ingredients down faster, so a bottle left in a hot car all summer may fail sooner.
The strongest evidence comes from a randomized trial in Nambour, Australia (Green and colleagues, Journal of Clinical Oncology, 2011). Researchers assigned 1,621 adults to either daily sunscreen on the head and arms or their usual habits, from 1992 to 1996, and then tracked them through 2006. The daily group developed 11 new melanomas and the comparison group developed 22. For invasive melanoma the gap was wider: 3 cases compared with 11.
