The sun feels harmless most days. It warms your skin, lifts your mood, and in many cultures a tan or a day outdoors is seen as a sign of health rather than risk. Underneath that warmth, though, is a form of invisible radiation that is doing measurable, cumulative damage to the skin and eyes with every unprotected exposure, whether you are in Lagos, Manila, Nairobi, or Mumbai.
This article explains what ultraviolet radiation actually is, what it does to the body, and what the latest research says about limiting exposure. It also separates the documented science from the myths that circulate about tanning, skin tone, and sun safety, since some of these myths cause real, avoidable harm.
What UV radiation actually is
Ultraviolet radiation, or UV, is a form of electromagnetic radiation that sits between visible light and X-rays on the electromagnetic spectrum, and it is invisible to the human eye [1]. It reaches the earth mainly from the sun, though artificial sources such as tanning beds also produce it [2].
UV radiation is divided into three types based on wavelength.
UVC has the shortest wavelength and the most energy, making it the most damaging type in theory, but it is almost entirely absorbed by the ozone layer before it reaches the earth’s surface, so it is not a meaningful part of everyday sun exposure [1, 3].
UVB has a medium wavelength and is the main cause of sunburn. It penetrates the outer layer of skin and is directly absorbed by DNA in skin cells, where it causes specific, well documented types of genetic damage [3, 4]. UVB makes up only about 5 percent of the UV radiation that reaches the earth’s surface, but it does a large share of the direct damage [4].
UVA has the longest wavelength of the three and makes up more than 95 percent of the UV radiation that reaches the ground [4, 5]. It penetrates deeper into the skin, reaching the dermis, the thicker layer beneath the surface, and is strongly linked to skin ageing, wrinkling, and melanoma [1, 5]. UVA can also pass through window glass, which UVB largely cannot [6].
How UV radiation actually damages the body
It damages DNA directly and indirectly
Even ordinary, everyday UV exposure can generate up to 100,000 DNA lesions per skin cell per day, which makes UV exposure the single most common outside source of DNA damage that humans experience, more common than damage from cigarette smoke [7]. UVB causes this damage directly, since its photons are absorbed straight into the DNA strand, creating specific distortions in the genetic code called pyrimidine dimers, which interfere with normal cell function and are strongly associated with the specific mutation patterns found in skin cancer tumours [4, 8, 9].
UVA works differently. Rather than hitting DNA directly, it is absorbed by other molecules in the skin, which then generate reactive oxygen species, unstable molecules that go on to damage DNA, proteins, and the collagen and elastin that keep skin firm [5, 9, 10]. This oxidative damage is a major driver of premature skin ageing, since it activates pathways in skin cells that break down collagen [10].
The body does have repair systems for this damage, including a process called nucleotide excision repair. But when UV exposure is frequent or intense, unrepaired damage accumulates over years, and this accumulation is what drives the transition from normal skin cells to cancerous ones [9, 11].
Skin cancer
The link between UV radiation and skin cancer is one of the most thoroughly documented relationships in cancer research. The World Health Organization classifies UV radiation as carcinogenic to humans and states that up to 90 percent of the global burden of melanoma and other skin cancers is attributable to UV exposure [3, 12].
A 2025 study from the International Agency for Research on Cancer, part of the World Health Organization, found that more than 80 percent of the roughly 332,000 cutaneous melanoma cases diagnosed worldwide in 2022 were directly attributable to UV radiation exposure [13]. This was a refined, more accurate estimate than earlier figures, and it specifically accounted for a rare type of melanoma called acral lentiginous melanoma, which is not caused by UV exposure and which makes up a larger share of melanoma cases in people with darker skin tones, showing that researchers are increasingly correcting older studies that did not fully account for how melanoma differs across skin tones [13].
Globally, over 1.5 million cases of skin cancer were diagnosed in 2020, with more than 120,000 deaths linked to skin cancer that year [3]. A separate global analysis using Global Burden of Disease data found that surface UV radiation levels have generally been rising, with North Africa, the Middle East, and parts of Europe showing some of the highest melanoma risk linked to UV trends between 1990 and 2021 [14].
Skin ageing
Beyond cancer, UV exposure is the dominant cause of what dermatologists call photoageing, meaning wrinkles, loss of elasticity, and uneven skin tone that come from sun exposure rather than the passage of time alone. This happens because UV radiation, especially UVA, triggers enzymes that break down collagen and elastin, the structural proteins that keep skin firm and smooth [5, 10].
Eye damage
UV radiation does not stop at the skin. The World Health Organization states that worldwide, an estimated 15 million people are blind due to cataracts, and roughly 10 percent of these cases may be linked to UV exposure [3]. Chronic UV exposure, even at relatively low doses over time, is a documented risk factor for cataracts, a condition called pterygium, which is a fleshy growth on the surface of the eye, and rare cancers of the eye’s surface tissue [3, 15]. Short-term, high-dose exposure can also cause photokeratitis, a painful, sunburn-like inflammation of the eye’s surface, sometimes called snow blindness [3, 15].
Importantly, research shows that the risk of UV-related eye damage is independent of skin type. Having darker skin offers essentially no protective advantage for the eyes, since the mechanism of damage is different from skin cancer [16].
Immune suppression
UV radiation, both UVA and UVB, has a documented immunosuppressive effect on the skin and, to some degree, on the wider immune system [3, 17]. This matters because immune suppression in the skin plays a direct role in allowing damaged cells to survive and develop into skin cancer, rather than being cleared by the immune system as they normally would be [3, 17]. This same immunosuppressive property is also used medically, under close supervision, in treating certain inflammatory skin conditions, but that controlled medical use is very different from unprotected, everyday sun exposure [17, 18].
The one genuine benefit: vitamin D
It would be inaccurate to describe UV exposure as having no upside. UVB radiation triggers the skin to produce vitamin D3, which the body needs for healthy bones and which may play a role in immune regulation [3, 19]. The World Health Organization is clear, however, that only a small, fairly casual amount of sun exposure is needed to maintain healthy vitamin D levels for most people, and that the dangers from overexposure are considerably greater than the benefits of getting extra sun beyond that point [20].
This is a genuinely nuanced area of research. Some researchers have described a real “sun exposure dilemma,” where public health messaging has to balance encouraging enough sun exposure for vitamin D against the well established risks of skin cancer and eye disease, and note that this balance is not the same for every individual, since it depends on skin type, age, geographic latitude, and other factors [21]. What is not disputed is that this small vitamin D requirement does not justify long, unprotected sun exposure, since brief, incidental daily exposure during ordinary outdoor activity is generally enough [20].
Darker skin still needs protection, according to the evidence
This is one of the most consequential misunderstandings in global sun safety, and it deserves detailed treatment because it affects a large share of readers across Africa and Asia.
It is true, and documented, that melanin, the pigment responsible for skin colour, provides some natural UV protection. Darker skin contains more eumelanin, the form of melanin thought to offer the strongest protective effect, and research shows that very darkly pigmented skin can have an intrinsic sun protection factor, or natural SPF, in the range of roughly 10 to 15, compared with a natural SPF of around 3 in the lightest skin types [22, 23]. This is one reason non-melanoma skin cancers occur less often, and often in different body locations, in people with darker skin compared with those who have fair skin [22].
However, researchers are explicit that this natural protection is limited and is not a substitute for sun protection measures such as sunscreen, shade, and protective clothing [23, 24]. Even in the most darkly pigmented skin, natural melanin protection is nowhere near as strong as a basic sunscreen, and darker skin is still fully vulnerable to UVA-driven skin ageing, immune suppression, and eye damage, none of which depend heavily on skin tone [16, 24, 25].
There is also a documented and serious clinical consequence of the belief that darker skin does not need protection. While skin cancer occurs less frequently in people with darker skin, multiple studies show it is often diagnosed later and at a more advanced stage in this group, which contributes to notably worse outcomes. One widely cited figure from the American Cancer Society shows a five-year melanoma survival rate of around 70 percent for Black patients in the United States compared with around 94 percent for white patients, a gap researchers link partly to delayed diagnosis rather than the biology of the cancer itself [26]. A large international study covering more than 18,000 people across 25 countries found that lighter skin tone was associated with more frequent use of sun protection measures, suggesting that people with darker skin tones are, on average, adopting fewer protective habits even though they remain at real risk [27].
Darker skin also faces its own specific UV-related problem. UV and visible light exposure can trigger or worsen hyperpigmentation conditions such as melasma and post-inflammatory hyperpigmentation, dark marks that persist after skin irritation or injury, and these conditions are generally more common, longer lasting, and harder to treat in deeper skin tones [25, 28]. This means sun protection in this context is not only about cancer prevention but also about managing a very common cosmetic and dermatological concern across many communities in Africa and Asia.
Myths and beliefs not supported by the evidence
“You cannot get sunburned on a cloudy day”
This is false. Clouds block only part of UVB radiation, and the actual amount blocked depends heavily on cloud type, altitude, and time of year, while clouds block very little UVA radiation at all [29]. Studies suggest as much as 80 percent of the sun’s UV rays can still pass through cloud cover, which is why sunburn on an overcast day is a well documented and common occurrence [30].
“A base tan protects your skin from further sun damage”
This is a persistent and clearly disproven myth. A tan is not a sign of protection, it is direct visual evidence that skin cells have already been damaged by UV radiation, since a tan results from melanocytes producing extra melanin specifically in response to that damage [29, 31]. Research cited by Harvard Medical School indicates that the protective effect of a tanning-bed base tan is roughly equivalent to a sunscreen with an SPF of only 3 to 4, far below the SPF of 30 or higher that dermatologists generally recommend [32]. Every additional tanning session adds further accumulated damage rather than building meaningful protection [29, 31].
“Tanning beds are a safer way to tan than the sun”
This is also false and is taken seriously by international health bodies. Tanning beds can emit UV radiation three to five times more intense than midday sunlight, and the World Health Organization has placed tanning devices in its highest cancer risk category [29, 33]. Multiple studies link indoor tanning bed use to an increased risk of melanoma [29].
“People with dark skin do not need sunscreen because their skin cannot burn or develop cancer”
As detailed above, this is a documented myth with real clinical consequences, not a minor exaggeration. Darker skin has meaningfully lower but not zero skin cancer risk, faces equal risk of UV-related eye and immune effects, and tends to experience worse cancer outcomes when it does occur, largely due to delayed diagnosis linked in part to this exact belief [23, 26, 27].
“Sitting under a beach umbrella means you do not need sunscreen”
This is only partly true and is worth clarifying rather than fully endorsing or fully rejecting. An umbrella blocks direct overhead sun, but it does not block indirect UV radiation reflected upward from surfaces such as water, sand, and pale concrete, all of which can still cause sunburn even while sitting in what looks like full shade [29].
A practical, internationally relevant takeaway
The underlying science points to a consistent, well supported set of practical steps that apply regardless of climate or skin tone: seeking shade during the strongest sun hours, generally between about 10 in the morning and 4 in the afternoon, wearing protective clothing and sunglasses, and using a broad spectrum sunscreen that protects against both UVA and UVB rays whenever the UV index is 3 or higher [3, 25]. The World Health Organization specifically recommends checking the UV index, a standard international scale that many national weather services now publish daily, as a simple, evidence-based way to judge when sun protection is genuinely necessary [3].
None of this means the sun should be avoided altogether, since a small amount of casual, everyday exposure supports healthy vitamin D levels [20]. The documented evidence simply does not support the popular idea that sun exposure is either entirely safe or that it only matters for people with fair skin. UV radiation affects everyone’s skin, eyes, and immune system to some degree, and the difference between a tan, a burn, cataracts, and skin cancer is often a matter of cumulative, largely invisible exposure over many years rather than any single afternoon outdoors.
This article is for general information and does not replace personalised medical advice. If you notice a new or changing mole, a sore that will not heal, or have concerns about a family history of skin cancer, it is worth speaking with a doctor or dermatologist directly. If you spot anything in this article that needs correcting or updating, please reach out to us with feedback.
Reference
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- [2] Ultraviolet radiation, World Health Organization
- [3] Ultraviolet radiation, World Health Organization
- [4] Molecular Regulation of UV-Induced DNA Repair, PMC
- [5] Oxidatively-generated damage to DNA and proteins mediated by photosensitized UVA, PMC
- [6] Top Myths About Tanning and Sun Protection, Everything Zoomer
- [7] Transcription and DNA repair collide after UV exposure, PNAS
- [8] UVA Radiation, DNA Damage, and Melanoma, ACS Omega
- [9] Mechanisms of UV-induced mutations and skin cancer, PMC
- [10] Ultraviolet Radiation Biological and Medical Implications, PMC
- [11] UV Radiation in DNA Damage and Repair Involving DNA Photolyases and Cryptochromes, PMC
- [12] Health consequences of excessive solar UV radiation, World Health Organization
- [13] New study results show UV radiation is responsible for more than 80 percent of melanoma cases worldwide, International Agency for Research on Cancer
- [14] Global assessment of surface ultraviolet radiation and malignant skin melanoma incidence from 1990 to 2021, Scientific Reports
- [15] An epidemiological perspective of ultraviolet exposure public health concerns, Australian National University Research Portal
- [16] Health Impacts of Exposure to UV Radiation, UK Department for Environment, Food and Rural Affairs
- [17] Effects of UV radiation, European Commission Scientific Committees
- [18] Health Impacts of Exposure to UV Radiation, UK Department for Environment, Food and Rural Affairs
- [19] Health effects of sunlight exposure, Wikipedia
- [20] Health consequences of excessive solar UV radiation, World Health Organization
- [21] An epidemiological perspective of ultraviolet exposure public health concerns, Australian National University Research Portal
- [22] The Protective Role of Melanin Against UV Damage in Human Skin, PMC
- [23] Beyond Melanin: A Literature Review of Photoprotection Mechanisms and Gaps in Skin of Color, PMC
- [24] Sunscreen 101, SPF Guide for Melanin-Rich Skin, Black Girl Sunscreen
- [25] Photoprotection for people with skin of colour, needs and strategies, British Journal of Dermatology, Oxford Academic
- [26] The Importance of Sunscreen for Dark Skin Tones, Cleveland Clinic
- [27] Photoprotection for people with skin of colour, needs and strategies, British Journal of Dermatology, Oxford Academic
- [28] Sunscreen for Skin of Colour, Why Melanin Isn’t Enough, Cantabria Labs
- [29] Top Myths About Tanning and Sun Protection, Everything Zoomer
- [30] Five myths about skin cancer, Prevent Cancer Foundation
- [31] The Truth About 7 Sun Protection Myths, Uniprix
- [32] Common Myths of Sunshine and Sunscreen, FEP Blue
- [33] Debunking Common Myths About UV Exposure, Olansky Dermatology
