Sunscreen myths: what's true out of what people say about it?

I'm a cosmetology student. Cloud only filters out part of UV radiation physically, a significant share still gets through.

I didn't find a precise figure for what percentage of UV passes through an average cloud layer, so I'm not writing a number here. What I can say from sources: UV radiation directly damages DNA in skin cells, and if the cell repairs this damage incorrectly, a genetic mutation is left behind.1 This mechanism doesn't depend on whether you can see the sun in the sky, and it's covered in detail in the article on UV radiation.

What you can take from this: cloud gives unreliable, unpredictable protection, so your daily sunscreen routine should be decided by whether you're outside during the day, not by the weather.

False. Darker skin reduces, but doesn't eliminate, the risk of UV damage. According to Leybengrub and colleagues' 2026 literature review, darker skin's higher eumelanin-to-pheomelanin ratio and more mature melanosomes provide natural photoprotection, but this protection isn't complete: skin cancer incidence is lower in dark skin, while mortality is higher, likely due to late diagnosis or misdiagnosis. The authors state this in so many words: darker-skinned populations are also susceptible to UV-induced skin damage, which can lead to the worsening of various dermatological conditions, including pigmentary disorders, photo-induced skin lesions and skin cancer.2

There's another reason to be careful about decisions based on skin type. According to Olsen and colleagues' 2026 review, the Fitzpatrick scale (a self-reported, six-category questionnaire about how your skin reacts to the sun), widely used to measure skin type, has received considerable criticism: it's self-reported, the wording of the questions varies, its range is limited, and it underestimates skin cancer risk.3 So it isn't even certain that someone would know exactly where to place themselves on this scale.

What you can take from this: lower risk doesn't equal zero risk, and darker skin doesn't exempt you from daily sunscreen either.

This falls down on quantity. SPF measurement is done with 2 milligrams of sunscreen per square centimetre, this is worked through in detail in the article on sunscreen types; a thinly applied foundation or powder doesn't come close to that amount. I didn't find a precise source for whether a makeup product labelled SPF on its own replaces separately applied sunscreen, but given the quantity principle, it's unlikely that a thin layer of makeup delivers the same amount as sunscreen applied separately for that purpose. This is my own reading, not a measured fact.

What you can take from this: SPF-labelled makeup is a supplement, not a replacement; sunscreen should be the last skincare step, before makeup, as the article on the minimum routine also describes.

I didn't find a direct clinical study comparing the breakout risk of physical and chemical sunscreens. What I can say, as my own reading, not a measured fact: comedogenicity (the tendency to clog pores) is a matter of formulation, mainly the oily base ingredients, not whether the sunscreen contains a mineral or chemical filter.

What you can take from this: if your skin is acne-prone, the product's full ingredient list matters, not whether you pick a "physical" or "chemical" sunscreen.

Partly true. Normal, non-UV-filtering window glass absorbs most of the UVB radiation responsible for sunburn, but lets a significant portion of UVA radiation through. This is a physical, optical principle, following from wavelength-dependent glass absorption, not a claim from a clinical study. This means that indoors, next to a window, in a car or in an office, you're mainly exposed to UVA, which rarely causes sunburn. UVA radiation is one of the documented causes of premature skin ageing: according to the European Commission's 2006 recommendation, every sunscreen should reach a minimum UVA protection level partly for this reason.5

I didn't find a precise percentage for how much UVA passes through an average window pane, so I'm leaving that sentence without a number.

What you can take from this: "it doesn't burn through a window" may be true for sunburn, but it doesn't mean you're free of UV exposure; on long car journeys or at a desk next to a window, this UVA load adds up.

I go through this question in detail in the article on sunscreen types: protection depends on the laboratory SPF number together with the amount applied, and I didn't find a study on whether an SPF100 product would last longer than an SPF30 one. Here I'll just add: a higher number doesn't fix a quantity problem if you apply it thinly.

I take this fear apart in detail in the carcinogenic chapter of the article on sunscreen types. Briefly: the chemical UV filters studied (avobenzone, oxybenzone and others) do enter the bloodstream. This was measured by US regulatory studies, using generous doses: applied to 75 percent of the body surface, and in the 2020 study even after a single application. This isn't a typical daily face routine, and the authors themselves state that this isn't a reason to avoid sunscreen. The 2021 benzene issue, meanwhile, was a manufacturing contamination, not a property of the active ingredients. The "carcinogenic" myth was born from conflating these two separate stories, not from a measured carcinogenic effect.

For this question ("does sunscreen prevent skin cancer"), the best data comes from Green and colleagues' 1999 Australian trial of 1621 people,4 also gone through in detail in the article on UV radiation. For squamous cell carcinoma (SCC), daily sunscreen use measurably produced fewer tumours; for basal cell carcinoma (BCC) there was no effect on tumour count. For the question of whether anyone developed a new cancer at all, though, there was no detectable difference for either type, and an independent review rated this evidence as low certainty. The same participants' long-term follow-up for melanoma sits at the edge of statistical reliability for the whole group, but was detectable for invasive (already spread into the skin's deeper layer) cases, based on few cases; this is presented in detail in the article on UV radiation.

This is actually the reverse: tanning (increased melanin production) is presumably the skin's defensive response to UV-induced cell stress. This is my own reading, not a literal statement from the Yang and Lan review: the review describes DNA damage and reactive oxygen species as the mechanism of UV-caused skin cancer, but doesn't discuss tanning as a defensive response.1 A more direct, but different kind of source is Cui and colleagues' 2007 experiment on mouse skin and cell culture: they showed that UV-induced pigmentation is driven by the p53 protein (one of the cell's central regulators responding to DNA damage).6 This is animal and cell-experiment data, not evidence directly about humans. I also go through this mechanism in detail in the article on UV radiation.

What you can take from this: tanning may signal that cells have possibly responded to a UV load, but these sources don't state whether the speed or depth of tanning in a given person is proportional to the extent of DNA damage; it's therefore a reaction to a signalled load, and its extent can't be read off from the tan.

This myth comes from the false assumption that UV radiation is an experience tied to sunbathing, not a constantly present factor. Each of the points above (cloudy weather, window glass) shows exactly that UV exposure doesn't only reach you at the beach or in summer: some UV reaches your skin in an office, next to a window, on a cloudy day, or on a walk in the city too. This is why the third step of a skincare routine is sun protection, every day, not just in summer; I go through this in more detail in the article on the minimum routine.

What you can take from this: the deciding question is whether you're outside during the day, in any season, not whether you're going to the beach.