The sun reaching your skin today is, in many places, measurably stronger than it was a few decades ago. That is not an illusion or nostalgia for milder summers. Since the late 1980s, the amount of solar radiation hitting the ground across much of the Northern Hemisphere has been increasing, a trend scientists call “brightening.” But the atmosphere is only part of the story. Changes in where you live, what medications you take, how much time you spend in air conditioning, and even how old you are can all make the same sunshine feel dramatically more punishing than it once did.
Cleaner Air Actually Lets More Sunlight Through
For much of the twentieth century, industrial pollution was inadvertently shielding people from the sun. Sulfur dioxide, soot, and other aerosols pumped into the atmosphere by factories and power plants scattered and absorbed incoming sunlight before it could reach the ground. Researchers documented a slow decline in surface solar radiation at weather stations around the world through the 1980s, a phenomenon called “global dimming.”1PubMed. From dimming to brightening: decadal changes in solar radiation at Earth’s surface Then, as clean-air legislation took hold in Europe and North America, aerosol levels dropped and the trend reversed. From about 1990 onward, surface solar radiation started climbing. The dimming gave way to brightening.
In Europe, where this shift has been studied most closely, the increase in sunlight at the surface is substantial. A recent analysis using satellite data found that changes in cloud properties and cloud cover account for roughly 80% of the brightening, while the direct reduction in aerosol pollution explains the remaining 20%.2Remote Sensing of Environment. Study finds reduction of aerosols and cloud cover drives increase in solar radiation in Europe But those two numbers are tangled together. Aerosols do not just block sunlight on their own; they also seed cloud formation and make clouds more reflective. When the atmosphere gets cleaner, clouds form with fewer but larger water droplets, which lets more light pass through. So the aerosol cleanup has a compounding effect, simultaneously removing its own direct shade and making the remaining clouds less effective as sunshields.
Italian records spanning more than five decades show the same pattern. Surface solar radiation declined until the mid-1980s and then rose, with the strength of the trends varying by season. Under clear skies, the dimming phase was even steeper than the all-sky measurements suggested, because cloud variability partially masked the aerosol signal during the pollution era.3Atmospheric Chemistry and Physics. Detection of dimming/brightening in Italy from homogenized all-sky and clear-sky surface solar radiation records and underlying causes (1959–2013) In other words, pollution was quietly doing more to filter the sun than many people realized, and its removal has left the atmosphere more transparent than at any point in living memory for many regions.
Global warming adds another layer. Rising temperatures reduce overall cloud formation in some regions, which further increases the amount of sunlight reaching the ground.2Remote Sensing of Environment. Study finds reduction of aerosols and cloud cover drives increase in solar radiation in Europe The result is a feedback loop: cleaner air and a warmer climate both conspire to make sunny days sunnier.
What the Ozone Layer Does and Does Not Explain
When people ask why the sun feels harsher, the ozone layer is usually the first suspect. And ozone does matter, but the story is more nuanced than the headlines from the 1990s might lead you to expect. The Montreal Protocol, signed in 1987, phased out the worst ozone-depleting chemicals, and the ozone layer has been slowly recovering since. Without that treaty, sunburning UV radiation at latitudes below 50° would have risen by 10 to 20% between 1996 and 2020. Over the Antarctic, the increase would have exceeded 100% during spring.4PubMed Central. Stratospheric ozone, UV radiation, and climate interactions The protocol averted a genuine crisis.
But “recovering” is not the same as “recovered.” Ozone levels remain below their pre-depletion baselines in many regions, meaning UV exposure at the surface is still somewhat elevated compared to the early twentieth century. Looking ahead, models project that erythemal UV at mid-latitudes will decrease by only about 2 to 6% between 2015 and 2090 as ozone continues to rebuild, assuming all countries keep their treaty commitments.4PubMed Central. Stratospheric ozone, UV radiation, and climate interactions Outside the polar regions, the projected UV decreases from ozone recovery are relatively small, less than 10%.5PubMed. Ozone depletion and climate change: impacts on UV radiation So while the ozone layer is no longer in freefall, it has not bounced back enough to cancel out the brightening effect from reduced aerosols. If anything, the two trends have been working in the same direction for the past few decades: less pollution above us and a still-thin ozone shield together mean more UV reaches your skin.
The Sun Itself Has Not Changed Much
If you are wondering whether the sun itself is ramping up its output, the answer is: barely. The sun does go through an 11-year activity cycle, during which its total radiative output fluctuates by about 0.1%. That is not nothing, but it is far too small for you to feel on your skin. The UV portion of the spectrum swings more than the total, but even there the numbers are modest. Over a full solar cycle, UV radiation between 200 and 300 nanometers varies by about 1.1%, and UV between 300 and 400 nanometers changes by roughly 0.25%.6Journal of Geophysical Research: Atmospheres. Detection and parameterization of variations in solar mid‐ and near‐ultraviolet radiation (200–400 nm) At wavelengths closer to the extreme ultraviolet, the variation is much larger, nearly a factor of two near 121.6 nanometers, but those wavelengths are absorbed high in the atmosphere and never reach the ground.7Advances in Space Research. The solar cycle variation in ultraviolet irradiance
The variation in sunlight that matters to your daily experience is driven overwhelmingly by the atmosphere, your local geography, and your own body. The sun’s output changes are a rounding error by comparison. This is worth knowing because it rules out one popular theory: the idea that the sun is simply “getting hotter.” It is not, at least not on any timescale relevant to whether you got a worse sunburn this summer than last.
Altitude and Reflected Surfaces
If you have ever been surprised by a fierce sunburn at a ski resort or on a mountain hike, the reason is straightforward: there is less atmosphere above you to filter the light. Measurements in the Alps and the Andes show that erythemal UV, the wavelengths responsible for sunburn, increases by about 18% for every thousand meters of elevation gain under clear skies.8Journal of Photochemistry and Photobiology B: Biology. Increase in solar UV radiation with altitude Total solar irradiance goes up by roughly 8% per thousand meters, while UVA radiation climbs by about 9%.8Journal of Photochemistry and Photobiology B: Biology. Increase in solar UV radiation with altitude Measurements in the Chilean Andes found a similar pattern, with UV-B increasing by about 8 to 10% per thousand meters.9Solar Energy. The effect of altitude upon the solar UV-B and UV-A irradiance in the tropical Chilean Andes
These percentage jumps compound. A city at 2,500 meters above sea level can receive roughly 45% more sunburning UV than a coastal town at the same latitude on the same day. Add snow cover or a reflective lake surface bouncing UV back up at you, and effective exposure climbs further. People who relocate from lowland cities to mountain towns, or who take vacations at high altitude without adjusting their sun habits, often learn this the hard way.
Cities Amplify the Heat
Even at sea level, your surroundings shape how intense the sun feels. Cities are thermal amplifiers. Dark asphalt, concrete, glass, and steel absorb solar energy during the day and radiate it back as heat. Asphalt in particular is a major offender: dense asphalt concrete has low reflectivity and high heat capacity, which means it soaks up sunlight efficiently and can reach surface temperatures above 60°C on hot summer days.10PubMed. The urban heat island effect, its causes, and mitigation, with reference to the thermal properties of asphalt concrete That heat radiates outward in the infrared range, warming the surrounding air and your body from below even as direct sunlight warms you from above.
This urban heat island effect means city dwellers experience the sun in a fundamentally different way than people in rural or forested areas. A parking lot at noon is not just hot because of the sun overhead; it is hot because the ground beneath your feet is re-emitting stored heat. The infrared radiation from hot pavement is invisible, but your skin senses it as warmth. Recent research has identified specific heat-sensitive receptors in the skin, transient receptor potential (TRP) ion channels, that respond to near-infrared radiation and even small temperature changes.11Journal of Photochemistry and Photobiology. Role of opsins and light or heat activated transient receptor potential ion channels in the mechanisms of photobiomodulation and infrared therapy Infrared radiation from sun-baked surfaces also contributes to oxidative skin damage, independent of UV.12PubMed. Beyond UV radiation: a skin under challenge So the intensity you feel in a city is not just subjective discomfort; your skin is genuinely absorbing more radiation from more directions.
Medications That Make Your Skin React to Light
Sometimes the sun has not changed at all, but your sensitivity to it has. Drug-induced photosensitivity is more common than most people realize. Nearly 400 different drugs or drug compounds have been reported to cause phototoxic or photoallergic reactions when combined with UV or visible light exposure.13PubMed Central. Drug-induced photosensitivity: culprit drugs, potential mechanisms and clinical consequences These span a wide range of drug classes: common antibiotics like doxycycline, certain blood-pressure medications, nonsteroidal anti-inflammatory drugs, and even some antidepressants. If you recently started a new medication and noticed that the sun feels more punishing, the drug may be the explanation rather than the weather.
Phototoxic reactions, the more common type, work like a chemical amplifier for sunlight. The drug molecules in your skin absorb UV energy and generate reactive oxygen species that damage cells directly. The result is an exaggerated sunburn response that can appear within hours. Photoallergic reactions are rarer and involve an immune response triggered by the combination of drug and light. Either way, the practical upshot is the same: a dose of sun that would have been unremarkable before the medication can now cause painful burns or rashes. Pharmacists often mention sun sensitivity when dispensing these medications, but the warnings tend to be buried among other side effects and easy to forget.
Age, Air Conditioning, and Your Changing Tolerance
Your body’s ability to cope with heat changes over time, and in ways that can make the sun feel more oppressive even when nothing about the sun itself has shifted. As you age, your thermoregulatory system becomes less efficient. Older adults require a larger rise in core body temperature before their skin blood vessels open up to dump heat. In one study, the threshold for activating the skin’s cooling response was about 1.3°C of core temperature rise in older adults compared to about 0.8°C in younger people, and once the response kicked in, its sensitivity was diminished.14PubMed Central. Thermoregulatory reflex control of cutaneous vasodilation in healthy aging The result is that the same sunny afternoon that felt tolerable at 30 might feel oppressive at 65, not because the conditions changed but because your cooling system has lost a step.
Air conditioning creates a different kind of vulnerability. People who spend most of their time in air-conditioned spaces lose some of their physiological and psychological acclimatization to heat. A study in Rio de Janeiro found significant differences in thermal sensation between people who regularly used air conditioning at home or work and those who did not. Air-conditioning users reported greater discomfort at the same outdoor temperatures, and when researchers applied these differences to annual climate data, the percentage of hours classified as heat stress rose substantially for the AC-using group.15Building and Environment. Implications of air-conditioning use on thermal perception in open spaces: A field study in downtown Rio de Janeiro A field study in Tempe, Arizona, found a related pattern: people who had been in air conditioning five minutes before stepping outside actually reported feeling more comfortable initially at above-neutral temperatures, suggesting a lagged perceptual response that could lead them to underestimate their heat exposure.16PubMed Central. Impact of shade on outdoor thermal comfort-a seasonal field study in Tempe, Arizona
The paradox is stark. Air conditioning protects you from heat indoors but erodes your ability to handle heat outdoors. As AC use increases globally, more people are spending more of their lives in artificially cool environments, which means the transition to outdoor sun feels more jarring than it would for someone acclimatized to warmer conditions. The sun has not gotten worse for these people; their baseline comfort has shifted.
Skin Pigmentation and Living in the Wrong UV Zone
Human skin pigmentation evolved over tens of thousands of years to match the UV environment of particular latitudes. Darker skin protects against UV damage in the tropics, while lighter skin allows more UV penetration for vitamin D synthesis in higher latitudes. Modern life has scrambled this ancient calibration. High-speed migration and urbanization have placed many people in UV environments radically different from those their ancestors adapted to, creating health risks on both sides of the mismatch.17PubMed Central. Human skin pigmentation, migration and disease susceptibility
People with lighter skin who move to tropical or high-altitude regions face a higher risk of sunburn and skin cancer. People with darker skin who move to northern latitudes risk vitamin D deficiency, which has been linked to conditions including rickets and multiple sclerosis.17PubMed Central. Human skin pigmentation, migration and disease susceptibility Neither group is “wrong” for their skin type; they are simply living in a UV regime their biology did not evolve to handle. For someone who grew up at a high latitude and relocated to a sunnier region, the sun genuinely is more biologically intense for them, independent of any atmospheric trends. It is a mismatch problem, and it affects hundreds of millions of people worldwide.
Air Pollution as Both Shield and Attacker
The relationship between air quality and sun intensity contains a counterintuitive twist. As discussed earlier, reducing aerosol pollution lets more sunlight through, which increases UV and total radiation at the surface. But pollution itself is not harmless to skin. Ambient air pollutants, including particulate matter and ozone at ground level, compromise the skin’s structural integrity and trigger oxidative stress and inflammatory responses.18PubMed Central. Environmental Air Pollutants Affecting Skin Functions with Systemic Implications Visible light and infrared radiation interact with pollutants deposited on the skin to amplify damage.12PubMed. Beyond UV radiation: a skin under challenge
This means there is no free lunch in either direction. Polluted air dims the sun somewhat but attacks your skin chemically. Cleaner air lets more radiation through but removes one source of skin stress. For someone living in a city that has recently cleaned up its air, both effects are in play: more sunlight is reaching them and less particulate is landing on their skin. The net health outcome depends on the specifics, but in either case the sun’s perceived intensity shifts. Cleaner air means the noon sun hits harder, even if your skin is no longer marinating in soot.
Why It All Adds Up
No single factor explains why the sun feels more intense. In most cases, several of these mechanisms stack on top of each other. You might live in a region where aerosol levels have dropped, increasing surface radiation by a meaningful percentage. You might spend your days in air conditioning, reducing your heat acclimatization. You might take a medication that sensitizes your skin to UV. You might have moved to a sunnier latitude or a higher altitude than where you grew up. Each factor nudges the dial independently, and they compound. Someone experiencing all four at once is living in a legitimately different solar environment than they were a decade or two ago, even though the sun’s own output has barely changed.
The practical response is fairly simple. Sunscreen, shade, and timing your outdoor exposure around peak UV hours matter more now than they did when the atmosphere was dirtier, especially in regions that have seen the strongest brightening trends. If you have started a new medication, check whether it is on the long list of photosensitizing drugs. If you are older, recognize that your body’s cooling system is less forgiving than it once was. And if you have relocated to a new climate zone, give yourself time to acclimatize and adjust your sun protection accordingly. The sun is not dramatically hotter, but the path between it and your skin has gotten a lot more transparent.