About 6.1 million American adults are treated for basal cell and squamous cell skin cancer every year, at a cost of roughly $8.9 billion. The Centers for Disease Control and Prevention reports that estimate, drawn from the federal Medical Expenditure Panel Survey.
Here is why you have probably never seen those two cancers in a statistics table. State cancer registries do not normally collect them, because they are too common. Registries track melanoma and rarer types such as Merkel cell carcinoma, so the country’s two most frequent cancers sit outside the official count.
CDC says most skin cancers trace back to a single exposure. This article is about that exposure: what ultraviolet radiation is, how to read the daily forecast, what blocks it, what a sunscreen bottle is legally permitted to promise, and the one place where the advice has to hold two true things at once.
Two kinds of UV, and what the index measures
UVA and UVB damage differently
Ultraviolet radiation is light at wavelengths too short for your eyes to register. The Environmental Protection Agency sorts it into three bands, and only two matter at ground level.
UVA has the longest wavelength. The atmosphere does little to stop it, so most of the UV reaching you is UVA, and it penetrates to the deeper layers of skin. EPA connects it to skin aging, eye damage, weakened resistance to illness and skin cancer risk. UVB is shorter, does not reach as deep, and is the band that burns you. The atmosphere blocks most of it, and how much gets through depends on latitude, altitude and time of year. UVC is shorter still and never arrives at all.
Two things follow. A product that prevents burning is not automatically stopping the deeper exposure, which is why broad spectrum exists as a regulated phrase. And feeling cool tells you nothing, because warmth is infrared while UV produces no sensation at all, which is why sunburn shows up hours late. EPA also puts a figure on the cumulative effect: up to 90 percent of the visible skin changes people attribute to aging are caused by the sun.
What changes your dose
EPA builds the UV Index from a satellite-based forecast of next-day stratospheric ozone plus the angle of incoming sunlight, estimating ground-level strength at every wavelength from 280 to 400 nanometers. Each wavelength is weighted by how strongly it reddens human skin, using a standard curve called the McKinlay-Diffey erythema action spectrum. The weighted total is adjusted for elevation and cloud cover, divided by 25, and rounded.
That division by 25 is the only reason the scale runs from about 0 to 11 instead of 0 to 300. It is an index, not a measurement of anything physical.
The adjustments carry the useful numbers. EPA’s figures for cloud: a clear sky passes virtually 100 percent of UV, scattered cloud 89 percent, broken cloud 73 percent, overcast 31 percent. Read the third one again. Broken cloud still delivers nearly three-quarters of the dose.
Elevation adds about 6 percent per kilometer above sea level, and CDC notes that UV reflects off snow, water, sand and cement, so some of it reaches you twice. CDC’s action threshold is an index of 3 or above, and EPA’s top band of 8 or higher comes with a rule you can use without a phone: if your shadow is shorter than you are, find shade.
Prevention has an order, and sunscreen is not at the top
Read CDC’s prevention guidance closely and you notice what the summaries drop. Sunscreen appears there conditionally.
The physical measures come first. Shade. Clothing over arms and legs. A wide-brimmed hat that shades face, ears and neck, which a baseball cap does not. Wraparound sunglasses blocking both UVA and UVB. Sunscreen enters as what you put on the skin clothing and a hat are not covering, or as the substitute when those are impractical. CDC also puts peak UV across the continental United States between 10 a.m. and 4 p.m. daylight saving time, which makes timing the cheapest control of all.
The reason for that ordering is simple. A shirt does not wash off, never needs reapplying, and does not depend on how thickly anyone spread it. A UPF rating states how much UV a fabric’s weave blocks, and article 717 covers those ratings.
The US Preventive Services Task Force, the federal advisory panel whose recommendations shape much of what clinicians do, graded counseling on sun protection in March 2018. For people aged 6 months through 24 years with fair skin, counseling to minimize UV exposure got a B, meaning recommended. For fair-skinned adults over 24 it got a C: offer it selectively, weighing individual risk, because the net benefit across that group is small. Counseling adults about examining their own skin got an I statement, which is a verdict on the research rather than on the practice.
What the randomized evidence shows
One randomized trial of daily sunscreen use has reported cancer outcomes, and a great deal rests on it.
In 1992, researchers in Nambour, a township in Queensland, Australia, randomly assigned 1,621 residents aged 25 to 75 to apply sunscreen daily to head and arms or to use it at their own discretion. Adèle Green and colleagues followed them for ten years past the trial and published the melanoma results in the Journal of Clinical Oncology in 2010.
By 2006 the daily group had 11 new primary melanomas against 22 in the discretionary group: hazard ratio 0.50, confidence interval 0.24 to 1.02, p value .051, just the wrong side of conventional significance. For invasive melanoma the result was clearer, 3 cases against 11, hazard ratio 0.27. Borderline on the headline, clear on the dangerous subset, in a subtropical setting with very high background UV and a comparison group that was not using nothing.
The National Cancer Institute reads the overall evidence more conservatively. Its patient summary says it is not known whether sunscreen lowers non-melanoma skin cancer risk, because not enough studies have been done, and that sunscreen used to prevent sunburn has not been proven to protect against UV-related melanoma. It does credit sunscreen with preventing sunburn and actinic keratoses, the scaly patches that can progress into squamous cell carcinoma.
Two federal bodies pointing different ways, because they answer different questions. CDC tells you what to do with today. NCI tells you what trials have proven.
What a sunscreen label is legally allowed to say
Sunscreen is regulated as an over-the-counter drug here, and the words on the front are controlled by federal regulation at 21 CFR 201.327.
SPF and broad spectrum
SPF is a sunburn number. FDA states that SPF values primarily indicate UVB protection, and the figure comes from testing on a human panel. The test only counts if a reference standard performs inside a narrow window, 16.3 plus or minus 3.43, so an SPF is a laboratory result rather than a property of the chemistry.
Broad spectrum is the UVA half, and it carries a numeric threshold almost nobody has heard. A product qualifies only if its mean critical wavelength, calculated from absorbance across 290 to 400 nanometers, reaches 370 nanometers or more. Fail, and the panel must read SPF alone and carry a bold alert as its first warning: this product has been shown only to help prevent sunburn, not skin cancer or early skin aging. A broad spectrum product below SPF 15 carries it too.
Only a broad spectrum product at SPF 15 or above may make a skin cancer claim, and even then FDA requires it to begin “if used as directed with other sun protection measures.” Any labeling implying that sunscreen alone prevents skin cancer makes the product misbranded. So the bottle is legally barred from saying what a lot of people believe it says, and three familiar words are banned outright: sunblock, waterproof and sweatproof.
Water resistant, for 40 or 80 minutes
Water resistance may be claimed in only two tested durations, and the label must say which. The directions have to match that time, and must also tell you to reapply immediately after towel drying and at least every two hours regardless. A product failing the test may not claim water resistance at all.
The gap between the label and your bathroom
SPF is measured at a defined thickness, 2 milligrams of product per square centimeter of skin, and almost nobody applies that much.
In a 2014 review in Photodermatology, Photoimmunology and Photomedicine, Bibi Petersen and Hans Christian Wulf found real-world application running between 0.39 and 1.0 milligrams per square centimeter, a quarter to a half of the tested amount, which cuts protection considerably. They also flag two failure modes nobody plans for: missed patches, and the UV you collect before applying anything. Rather than train people to use more, they proposed something simpler. Put it on before you go out, then reapply once within the first hour, because the second coat covers what the first missed.
FDA’s guidance lands in the same place: apply 15 minutes beforehand, use at least one ounce for an adult body, roughly a shot glass, and reapply at least every two hours. Treat SPF as a ranking between products, not a multiplier on how long you can stay out.
Where FDA’s sunscreen rules stand right now
Sunscreens sold here are governed by an over-the-counter monograph, the rule book setting which active ingredients and labels are acceptable without an individual drug approval. In March 2020 the CARES Act replaced monograph rulemaking with a faster administrative order process, and sunscreen’s existing rules carried over by operation of law into what FDA calls a deemed final order, built on a 1999 monograph that had been stayed plus labeling requirements from a 2011 rule. FDA posted that order on September 24, 2021, and the same day posted a proposed order carrying forward a 2019 proposed rule that was never finalized. That proposal drew more than 15,000 comments and remains a proposal. It would cap labeled SPF at 60 plus and require broad spectrum protection at SPF 15 and above.
On active ingredients, FDA has proposed that zinc oxide and titanium dioxide are generally recognized as safe and effective. Twelve others, oxybenzone and avobenzone among them, sit in a category that reads alarming and is not: FDA says it lacks sufficient safety data to decide, and states explicitly that this is not a conclusion that they are unsafe.
Two ingredients have now been finalized out. On September 10, 2026, FDA removed para-aminobenzoic acid, better known as PABA, and trolamine salicylate, finding their risks outweigh their benefits, and adding that it is aware of no sunscreen currently marketed here containing either. In June 2026 it went the other way and added bemotrizinol, its first new permitted active ingredient in roughly two decades.
Carry one procedural detail with you. A final order under this process cannot take effect until at least a year after it is issued, so when you read that FDA has banned or approved something in sunscreen, the next question is whether the order is in effect yet.
Tanning beds, and what a tan is
Take this correction straight from the agency. CDC states that “A suntan does not indicate good health.”
A tan is not a coating your skin applies in advance. It is what happens after UV has already reached living cells, as melanin moves toward the surface in response. Any change in skin color following UV exposure, tan or burn, means injury has occurred, so a base tan records damage rather than insuring against more.
Indoor tanning delivers high UV on purpose, and CDC links it over time to skin cancer and eye cancer. FDA reclassified sunlamp products as class II devices in 2014, subjecting them to premarket review, and required labeling stating they should not be used by anyone under 18. The agency has proposed restricting sale and use to adults 18 and over, and as of its own tanning page, last updated in May 2019, that proposal had not been finalized.
Vitamin D, and why this is the part for your clinician
Your skin makes vitamin D when bare skin absorbs UVB. That is real biology, and it is why sun advice has to hold two things at once.
What the evidence supports is narrower than either side of the argument usually concedes. An international panel of 13 specialists in endocrinology, dermatology, photobiology, epidemiology and biological anthropology published a consensus in the British Journal of Dermatology in 2019. Broad spectrum sunscreens that prevent skin reddening are unlikely to compromise vitamin D status in healthy people, they concluded. Their exception matters more: people with photosensitivity disorders, who need rigorous photoprotection combining high-SPF products, covering clothing and shade, are likely to have status compromised, and the panel advised screening and supplementation for that group specifically.
Read the author list before weighing it, because several authors were employed by a cosmetics manufacturer’s research division alongside the academic and clinical authors. That does not make the conclusion wrong. It is something a reader is entitled to know.
The National Cancer Institute, covering the same ground, lists lower vitamin D levels among the possible harms of sunscreen use, and in the same summary lists impaired vitamin D metabolism among the possible harms of avoiding the sun. Holding both at once is the honest position.
What you will not find here is a number. No exposure time, no target blood level and no supplement dose appears in this article, because the right answer depends on your skin, your latitude, your diet, your medications and your medical history, and because unprotected UV exposure is not a vitamin D strategy this article will recommend.
The routes that involve no UV are worth knowing. The NIH Office of Dietary Supplements says very few foods naturally contain vitamin D and that fortified products supply most of what Americans get, including milk and many plant-based milks, some cereals, orange juice and yogurt. It also names who is most likely to fall short, including older adults, people who rarely go outside, people with darker skin and people whose conditions impair fat absorption. If you recognize yourself there, the next step is a conversation with your own clinician, not a purchase. Article 720 covers light as a signal to your body clock, a separate pathway that runs through your eyes rather than your skin.
Checking your own skin, and when to make the call
Here the federal advisory panel and the dermatology profession diverge.
The Preventive Services Task Force issued an I statement in April 2023 on visual skin examination by a clinician as a screening test in asymptomatic adolescents and adults. A clinician’s exam detects melanoma with sensitivity of roughly 40 to 70 percent and specificity of 86 to 98 percent, the evidence that screening reduces deaths comes from non-randomized studies conducted mostly in Germany, and most accuracy data come from fair-skinned populations. None of that says looking at your own skin is pointless. It says the trials that would prove a screening program works have not been run.
Dermatologists are more direct. The American Academy of Dermatology teaches the ABCDEs for any mole or pigmented spot, and the letters get easier once you see what each is asking. Three concern shape and content: Asymmetry asks whether the halves would match if you folded the spot down the middle, Border asks whether the edge is ragged rather than a clean line, and Color asks whether there is more than one, such as tan with brown and black or flecks of white, red and blue in one lesion. Diameter concerns size, flagging spots wider than about 6 millimeters, roughly a pencil eraser, though the Academy notes melanomas are sometimes found smaller. And Evolving concerns time, the one a single glance cannot give you: the spot is changing in size, shape or color, or looks unlike the rest of yours.
The Academy’s plainer prompts are arguably more useful day to day: a spot that is new, a spot unlike your others, and a spot that is changing, itching or bleeding. For any of those it recommends a board-certified dermatologist. To make that practical, pick a fixed date each year, use a hand mirror for your back, and photograph anything you are unsure about with a ruler or a coin in the frame. Change is the signal, and you cannot see change without a baseline.
Reasons to stop reading and call someone: a sore that will not heal, a spot that bleeds without being knocked, a mole that has changed over the past few months, a new dark streak under a nail, or any ABCDE feature. If you have had a skin cancer before, or a parent, sibling or child has, the Task Force’s screening statement explicitly does not cover you, and surveillance becomes a conversation with a clinician who knows your history.
The two measures that never wear off
Shade and timing. Keep those two, because they are the only measures that work on your whole body, cost nothing, never wear off, and do not depend on how carefully you applied them.
Everything else fills gaps in that. Clothing and a hat cover what shade cannot, and sunscreen covers what clothing cannot. The number on the bottle describes a thicker application than yours, so treat SPF as a ranking and put the second coat on early.
Then check the index before deciding what today requires. An overcast sky still passes about a third of the UV, broken cloud nearly three-quarters, and your skin keeps score whether or not you felt warm.
Keep exploring: Endangered Species Act and environmental justice.
Sources
- Centers for Disease Control and Prevention. “Reducing Risk for Skin Cancer.” cdc.gov
- Centers for Disease Control and Prevention. “Skin Cancer Statistics.” cdc.gov
- Centers for Disease Control and Prevention. “Skin Cancer Risk Factors.” cdc.gov
- US Preventive Services Task Force. “Skin Cancer Prevention: Behavioral Counseling (final recommendation, 20 March 2018).” uspreventiveservicestaskforce.org
- US Preventive Services Task Force. “Skin Cancer: Screening (final recommendation, 18 April 2023).” uspreventiveservicestaskforce.org
- US Food and Drug Administration. “Sunscreen: How to Help Protect Your Skin from the Sun.” fda.gov
- US Food and Drug Administration. “Questions and Answers: FDA's Regulatory Actions for Over-the-Counter Sunscreen.” fda.gov
- US Food and Drug Administration. “Tanning (sunlamp products).” fda.gov
- Electronic Code of Federal Regulations. “21 CFR 201.327, Over-the-counter sunscreen drug products; required labeling based on effectiveness testing.” ecfr.gov
- US Environmental Protection Agency. “UV Index Scale.” epa.gov
- US Environmental Protection Agency. “Calculating the UV Index.” epa.gov
- US Environmental Protection Agency. “Health Effects of UV Radiation.” epa.gov
- US Environmental Protection Agency, RadTown. “Ultraviolet (UV) Radiation and Sun Exposure.” epa.gov
- National Cancer Institute. “Skin Cancer Prevention (PDQ) Patient Version.” cancer.gov
- NIH Office of Dietary Supplements. “Vitamin D: Fact Sheet for Consumers.” ods.od.nih.gov
- American Academy of Dermatology. “What to Look For: ABCDEs of Melanoma.” aad.org
- Journal of Clinical Oncology (retrieved via PubMed). “Green AC, Williams GM, Logan V, Strutton GM. Reduced melanoma after regular sunscreen use: randomized trial follow-up. 2011. DOI: 10.1200/JCO.2010.28.7078.” doi.org
- Photodermatology, Photoimmunology & Photomedicine (retrieved via PubMed). “Petersen B, Wulf HC. Application of sunscreen: theory and reality. 2014. DOI: 10.1111/phpp.12099.” doi.org
- British Journal of Dermatology (retrieved via PubMed). “Passeron T, Bouillon R, Callender V, et al. Sunscreen photoprotection and vitamin D status. 2019. DOI: 10.1111/bjd.17992.” doi.org