The Sun Question

There is a scene that repeats itself every summer on beaches across the Mediterranean: a mother sprays her toddler with an aerosol sunscreen — a white mist that settles on skin, hair, towels, and the air the child is breathing in — and feels, understandably, like a responsible parent. The message has been clear for decades: sun is the enemy, sunscreen is your shield. Apply liberally. Reapply often. Start young.

But what if the story is more complicated than that? What if some of the chemicals we have been rubbing into the most absorbent skin of our smallest children are disrupting their hormonal development? What if the sunscreens marketed as natural and mineral are not quite what they claim? And what if the cultural obsession with blocking out the sun entirely is generating its own category of harm — one that sits quietly in the background while melanoma rates continue to rise?

The sun is not simply a hazard to be managed. It is a biological signal, ancient and irreplaceable, that your body has been reading for hundreds of thousands of years. Learning to work with it, rather than against it, is the real sun question.

A Primer on UV Radiation

Sunlight reaches the skin as a spectrum. The portion most relevant to sunscreen discussions is ultraviolet radiation, which is divided into UVA (320–400nm) and UVB (280–320nm).

UVB penetrates only the upper layers of the skin — the epidermis — and is the primary driver of sunburn and, at sufficient dose, of the DNA damage that can initiate skin cancer. It is also the wavelength responsible for triggering vitamin D synthesis: it converts 7-dehydrocholesterol, a cholesterol derivative, into previtamin D3, which the liver and kidneys then activate into the hormone we call vitamin D. This is not a minor function. Vitamin D regulates calcium metabolism, modulates immune response, protects cardiovascular function, and influences gene expression in almost every tissue in the body. You cannot make it from behind glass, in the shade, or under sunscreen.

UVA penetrates deeper — into the dermis — and is the primary driver of photoaging, collagen degradation, and the oxidative damage linked to melanoma. It passes through cloud cover and glass, and is present throughout the day at relatively consistent intensity, unlike UVB, which peaks around solar noon. This distinction matters when we talk about SPF: most SPF ratings measure only UVB protection. Broad-spectrum sunscreens cover both, but the ratio is rarely communicated.

Then there is what sunscreen discussions almost never mention: the rest of the spectrum. Visible light, red light, and near-infrared radiation — which together constitute the majority of solar energy — are not hazards. They are active biological signals, ancient and precisely calibrated, that stimulate mitochondrial function, regulate circadian rhythms, and prime the skin's own antioxidant defences.

The Chemical Filter Problem

Modern sunscreens fall into two broad categories: chemical, or organic, filters, which work by absorbing UV radiation and converting it to heat; and physical, or mineral, filters — zinc oxide and titanium dioxide — which work primarily by scattering and reflecting UV.

Chemical filters dominate the market. They are cosmetically elegant, they go on clear, they blend easily. They are also the category drawing the most concern. The most scrutinised are oxybenzone (benzophenone-3), octinoxate (ethylhexyl methoxycinnamate), homosalate, avobenzone, and octocrylene. A 2024–2025 review of 75 epidemiological and human studies found significant associations between these filters and hormonal disruption: reduced testosterone in adolescent males, altered thyroid hormones in pregnant women, delayed pubertal development in boys, and earlier menarche in girls.

This is not fringe science. In 2025, the European Commission finalised its position that octinoxate is an endocrine-active substance — meaning it interferes with hormonal signalling. A 2023 review of 254 studies found mounting evidence that oxybenzone has endocrine-disrupting properties when sunscreen is applied normally, concluding that the most concerning consequence is potential reproductive harm. The regulatory framework, however, remains fragmented: oxybenzone is still freely sold in the US and Australia, while Hawaii and several Pacific jurisdictions have banned it for killing coral larvae at parts-per-trillion concentrations.

The endocrine-disruption concern carries particular weight for children, whose hormonal axes are actively developing. Oxybenzone and octinoxate exhibit estrogenic and anti-androgenic activity, interfere with steroidogenic enzymes, and modulate thyroid hormone — all through pathways that interact with the developing endocrine system. A 2025 review in Toxics documented the convergence between these filters' disrupting properties and the hormonal vulnerabilities underlying polycystic ovary syndrome, including hyperandrogenism and disrupted folliculogenesis.

None of this means that a single application of conventional sunscreen is a medical emergency. But it does mean that daily, whole-body application of these chemicals across an entire childhood — which is effectively what standard sun-safety messaging recommends — deserves far more scrutiny than it has received.

The Nanoparticle Question

If chemical filters raise biological concerns, mineral alternatives — zinc oxide and titanium dioxide — raise a different anxiety: particle size. In their conventional form, these minerals leave a white cast on the skin. In nanoparticle form, they spread more easily and go on more invisibly. The concern is whether particles small enough to disappear into skin could also penetrate it — and if they could, what they would do.

The research, taken in aggregate, is broadly reassuring, with one important caveat. Studies using multiphoton microscopy and advanced imaging have demonstrated that intact zinc oxide nanoparticles do not penetrate the viable epidermis in normal use conditions. They accumulate in skin furrows and the stratum corneum but do not reach living cells. This holds even when skin is barrier-impaired or occluded. The caveat concerns zinc ions released from the particles: these penetrate slightly deeper, and their cytotoxic potential at those concentrations remains less precisely defined.

The European Commission's Scientific Committee on Consumer Safety concluded that nanoparticulate zinc oxide and titanium dioxide are safe when applied to intact skin. Both the Australian TGA and the FDA concur, with the FDA noting the remaining data gaps concern photoactivation — ultraviolet exposure can activate certain uncoated titanium dioxide formulations and generate free radicals that may damage DNA.

The caveat that matters most for this article sits not on skin but in the lungs. There is clear evidence that zinc oxide nanoparticles can cause inflammation in lung tissue when inhaled. This makes the aerosol question urgent.

The Aerosol Problem

Spray sunscreens are ubiquitous. They are sold on the promise of convenience — no greasy hands, fast coverage, easy for wriggly children. They are, arguably, one of the more poorly considered products of the modern sunscreen market. The FDA has not cleared aerosol sunscreens as safe; it has requested additional data from manufacturers and has not received it. Consumer Reports has specifically recommended against their use on children. Here is why.

When an aerosol sunscreen is sprayed — particularly in the enclosed or semi-enclosed conditions typical of beach-bag application, inside a car, in a beach tent, in a bathroom — it produces a fine mist that hangs in the air. Children inhale this mist. If the product contains chemical UV filters like oxybenzone, those chemicals go directly into lung tissue and, since the lungs are far more absorptive than skin, into the bloodstream. If the product is mineral-based, the nanoparticles of zinc oxide or titanium dioxide that are perfectly safe on skin become potential pulmonary irritants when inhaled. Children with asthma are at particular risk, since any aerosol can trigger airway constriction.

There is also an efficacy problem. Sunscreen standards are based on applying two milligrams of product per square centimetre of skin. Aerosol application makes this essentially impossible to achieve — much of the mist is lost to the air or carried off by wind — meaning children are likely receiving far less actual UV protection than the label SPF implies, at the cost of chemical exposure. Several aerosol sunscreens have additionally been recalled after testing revealed contamination with benzene, a known human carcinogen that appears as a byproduct of the propellant chemistry rather than as an ingredient. Its presence in a product applied to children is not acceptable.

The simple message: avoid aerosol sunscreens entirely, particularly for children. A lotion requires more effort and slightly greasier hands. It also means your child is actually protected, and not inhaling whatever the can is spraying into the air around them.

Greenwashing and the Fine Print

The most useful thing you can do the next time you pick up a sunscreen labelled "natural," "mineral," "reef-safe," or "clean" is to read the full ingredient list. Not the front panel, not the marketing copy — the INCI list on the back.

The case that crystallised this for me recently was a Dutch brand marketed specifically for children, with the promise of a natural, zinc-based formulation and conspicuously clean branding. The front of the tube mentions zinc oxide. Read further and you find chemical UV filters — ethylhexyl salicylate, homosalate, or both — sitting in the ingredient list without any particular emphasis. The product is not pure mineral. It is a hybrid, and the marketing elides this.

This is not uncommon. "Mineral" in marketing copy does not mean exclusively mineral. "Natural" has no regulatory definition. "Reef-safe" is not legally defined in most jurisdictions, and a product can claim the label while containing filters shown to damage coral. "Zinc-based" simply means zinc is present — it says nothing about what else is in the formulation. The EU cosmetics regulation requires full INCI labelling, but it does not require that chemical filters be prominently disclosed alongside mineral ones. The consumer is left to decipher a list of Latin and systematic chemical names without a guide.

If you want a truly mineral sunscreen for your children, you are looking for products where the only UV filters are zinc oxide and/or titanium dioxide. Non-nanoparticle formulations are available if you prefer to avoid the nano question entirely — they will leave a white cast, but they will do what it says on the tin. For everyday use and for children, this is where I would direct my attention.

The Melanoma Paradox

Here is a fact that tends to get quietly buried in sun-safety communications: melanoma rates have risen significantly over the same decades that sunscreen use has increased. In the US, melanoma incidence in young men in 2009 was four times what it was in 1970; in young women, eight times as high. A 2023 systematic review in Cancers identified five candidate explanations — increased diagnosis, longer sun-exposure sessions enabled by sunscreen use, insufficient broad-spectrum protection, free-radical generation by some chemical filters, and confounding variables in study design.

The free-radical point is worth pausing on. Avobenzone — one of the most widely used chemical UVA filters — degrades in sunlight and generates free radicals. When combined with octinoxate, that degradation accelerates. Free radicals are exactly the mechanism by which UV radiation damages DNA and initiates carcinogenesis. A sunscreen that generates oxidative stress as it degrades is not straightforwardly protective.

The Stanford dermatology finding is perhaps the most counterintuitive: people who relied solely on sunscreen for sun protection got more sunburns than people who reported infrequent sunscreen use but wore hats and protective clothing. Sunscreen appears to extend time in the sun — its SPF rating gives people the confidence to stay out longer — without extending protection proportionally. It becomes a substitute for shade, hats, and timing. And that substitution, accumulated over a lifetime, may matter.

None of this means sunscreen causes melanoma. The association between sunburn and melanoma risk is well-established — five or more blistering sunburns between the ages of 15 and 20 increases lifetime melanoma risk by 80%. Protecting yourself from burning is genuinely important. But the dominant narrative — that sunscreen is the solution, apply it daily, more is better, always, from infancy — needs to be examined in the light of the evidence, not just repeated.

The Sun You Actually Need

The argument for avoiding the sun has been so thoroughly amplified that it has produced its own problem: epidemic vitamin D deficiency. An estimated 40% of US residents have overt deficiency, and the figures in Northern Europe are similar. The UK's NHS advises that between October and March, sunlight cannot produce adequate vitamin D at all — the sun's angle is simply too low for UVB to reach the skin effectively.

Vitamin D is not a minor nutrient. It functions more like a hormone, regulating calcium and phosphorus metabolism, modulating immune response, influencing gene expression across hundreds of genes, and playing roles in cardiovascular, neurological, and metabolic health. Low vitamin D status is associated with increased risk of autoimmune disease, cardiovascular disease, depression, and several cancers — including, with notable irony, melanoma.

The vitamin D–cholesterol connection is often skipped in public communication but is biochemically fundamental. Vitamin D3 is synthesised in the skin from 7-dehydrocholesterol, a derivative that sits at the end of the cholesterol synthesis pathway. UVB converts it to previtamin D3, while a competing enzyme converts the same precursor to cholesterol. Adequate cholesterol is therefore a prerequisite for robust vitamin D synthesis. The low-fat, low-cholesterol dietary prescriptions of recent decades are, in this light, part of a larger story about why vitamin D insufficiency is so prevalent. The foods once dismissed for their cholesterol content — egg yolks, liver, fatty fish, butter — are the same foods that have traditionally provided vitamin D directly and that support the substrate pool for its cutaneous synthesis.

Sunscreen blocks vitamin D production. SPF 15 reduces synthesis by approximately 99%. People who apply sunscreen every day, as public-health guidance recommends, will not produce meaningful amounts of vitamin D from sun exposure. This is not a side effect hidden in small print. It is physics.

Vitamin D is not the only reason your body needs the sun. Near-infrared and red light wavelengths reach deep into tissue and directly stimulate mitochondrial function: their absorption by cytochrome c oxidase in the mitochondrial respiratory chain drives ATP production and reduces oxidative stress. Near-infrared light also stimulates melatonin production within the mitochondria, functioning as an intracellular antioxidant that helps protect skin cells from UV damage. This is not the melatonin of the pineal gland and sleep cycles — it is a separate, local antioxidant system, activated by the same morning sun that starts the circadian day.

Sunlight also regulates serotonin synthesis, cortisol rhythms, nitric oxide release from the skin — which directly lowers blood pressure — and the complex signalling that synchronises every organ system to the 24-hour day. The circadian disruption associated with inadequate outdoor light is itself linked to increased cancer risk, metabolic dysfunction, cardiovascular disease, and impaired immunity. A life lived largely indoors, under artificial light, is a life lived in a state of chronic photonic malnutrition.

Morning Light as Preparation

This is the part of sun biology almost entirely absent from conventional sun-safety messaging, but that photobiology researchers have been documenting for years. Sunrise light is dominated by red and near-infrared wavelengths. The UV content in the early morning is low — at temperate latitudes in summer, negligible. What the morning sun delivers abundantly is the photobiomodulatory spectrum: the wavelengths that activate mitochondria, set the circadian clock through the suprachiasmatic nucleus, initiate serotonin production, and — critically — prime the skin for the more intense radiation that follows.

Early infrared exposure induces the production of melanin, the skin's natural UV filter. It activates heat-shock proteins and antioxidant defences. It stimulates mitochondrial melatonin production, which provides intracellular protection against UV-induced oxidative damage. The morning light, in short, is doing exactly what you might design a protective pre-treatment to do — except evolution got there first, because for most of human history you could not have UV exposure without having had infrared exposure first.

The practical implication is that someone who spends thirty minutes outside in the morning — ideally before or around the time the UV index rises — before longer midday exposure is in a meaningfully different physiological position than someone who goes directly from an air-conditioned office to a midday beach. Circadian biology, mitochondrial priming, and melanin preparation all point in the same direction: build a relationship with the sun across the day, rather than avoiding it entirely and then managing the midday window with SPF 50+.

The Fitzpatrick Framework

Not all skin negotiates the sun in the same way. The Fitzpatrick scale — developed by the Harvard dermatologist Thomas Fitzpatrick in 1975 — classifies skin into six phototypes based on melanin content and sun-response behaviour.

The biochemistry behind this is important. Eumelanin — the dark brown-black pigment — functions as an efficient free-radical scavenger, absorbs UV, and scatters light. It confers a natural SPF of around 13 in darker skin, compared to approximately 3 in very pale skin. This is a real and significant difference. Lighter skin types that originated in northern latitudes did so partly because reduced melanin allowed more efficient vitamin D synthesis in low-UV environments — a trade-off optimised over millennia.

Darker skin is more protected from UV damage but not immune. Melanoma in darker phototypes tends to present later — often on the palms, soles, or under the nails, where pigmentation is absent — and carries a worse prognosis because of delayed diagnosis. The message that dark-skinned people need not worry about the sun is wrong, and it has cost lives. The practical guidance is to personalise: a Fitzpatrick Type I redhead in Tuscany in July needs different strategies from a Type IV person of Mediterranean descent. Types I and II may genuinely need to avoid peak UV hours and use mineral sunscreen for extended exposure, while getting their sun in the morning and late afternoon. Types III to V can typically tolerate longer midday exposure and should be careful not to over-block the sun their bodies need for vitamin D and circadian health.

What Sensible Sun Practice Looks Like

After all of this, what does the evidence actually support? A few principles that are older than the sunscreen industry, and likely to outlast it.

Don't burn. This is the single most consistently supported intervention for reducing skin-cancer risk. A history of blistering sunburns — especially in childhood — is a genuine risk factor. Burning is not tanning. Burning is DNA damage and inflammation. Prevent it.

Hats and layers beat sunscreen for sustained exposure. The Stanford finding is counterintuitive but robust: people who wear hats and light protective clothing get fewer burns than people who rely on sunscreen alone. A linen shirt blocks UV. A wide-brimmed hat protects the face, neck, and shoulders — precisely the sites most prone to UV-related skin cancer. These are what humans wore in sunny climates for most of recorded history.

Don't take small babies to the beach between 11am and 3pm. In summer at temperate to Mediterranean latitudes, the UV index between these hours is at its highest. Infant skin is more permeable, the DNA-repair surveillance system is less mature, and thermoregulation is less efficient. Sunscreen on infants under six months is generally not recommended by most paediatric bodies — and the aerosol alternative is not a substitute. The beach at 8am and 5pm is beautiful and appropriate. The beach at 1pm in August with a four-month-old requires a proper shade structure and brevity.

Get morning light before high-UV exposure. Ten to thirty minutes of outdoor light in the morning — before the UV index rises significantly — sets your circadian clock, primes your mitochondria, builds melanin, and activates your skin's antioxidant defences. It is free. It takes no longer than a coffee on the terrace.

Choose mineral sunscreen when sunscreen is warranted. For extended midday exposure — particularly for fair skin types, at the beach, or at altitude where UV intensity increases — a mineral sunscreen (zinc oxide and/or titanium dioxide only, ideally non-aerosol) is the most defensible choice. Check the ingredient list. If ethylhexyl salicylate, oxybenzone, octinoxate, homosalate, avobenzone, or octocrylene appear anywhere, the product is not purely mineral.

Don't avoid the sun entirely. The downstream consequences of sun avoidance — vitamin D deficiency, circadian disruption, mitochondrial underfunctioning — are real and measurable.

The sun has been asking us the same question for as long as we have existed. The question is not how to block it — it is how to listen to it. To be outside in the morning. To build tolerance gradually, the way all sun-adapted organisms do. To eat the fat-soluble nutrients that make the system work. To protect yourself intelligently when the UV index is genuinely high. And to stop treating a star that your biology was calibrated to as something requiring management by the cosmetics industry.

The light is outside. Walk towards it.