The sun burns your skin because ultraviolet (UV) radiation damages the DNA inside your skin cells, triggering an inflammatory response that produces the redness, heat, and pain you recognize as sunburn. It’s not the warmth of sunlight doing the damage. You can get sunburned on a cool, cloudy day because UV radiation passes through clouds and operates independently of the heat you feel on your skin.
How UV Radiation Damages Your Skin Cells
Sunlight contains two types of ultraviolet radiation that harm your skin in different ways. UVB rays are absorbed almost entirely by the outermost layer of skin, the epidermis. There, they’re absorbed directly by your DNA, causing the molecular structure to buckle and form abnormal bonds between neighboring DNA bases. These malformed structures, called photoproducts, are the core injury behind a sunburn.
UVA rays penetrate much deeper, reaching well into the second layer of skin (the dermis). Rather than hitting DNA directly, UVA generates reactive oxygen species, unstable molecules that damage DNA, proteins, and cell membranes through a chain of chemical reactions. This deeper damage contributes to premature aging, wrinkles, and long-term skin cancer risk, even when you don’t visibly burn.
Why It Turns Red and Hurts
The redness and pain of sunburn aren’t caused by the UV exposure itself. They’re caused by your immune system’s response to the damage. When UVB radiation injures skin cells, it triggers a cascade of inflammatory signals. Damaged cells release powerful pro-inflammatory molecules that dilate blood vessels and recruit immune cells to the area. This flood of blood to the damaged skin is what creates the characteristic redness, warmth, swelling, and tenderness.
Pain typically starts within a few hours of sun exposure and peaks at about 24 hours, which is why a burn can look mild when you come inside and feel much worse the next morning. The delay happens because the inflammatory process takes time to fully ramp up. Your body is essentially treating UV-damaged skin the way it would treat any injury: sending in immune cells to clean up the mess and prevent further problems.
What Melanin Does (and Where It Falls Short)
Your skin’s primary defense against UV is melanin, the pigment that gives skin its color. Melanin works by absorbing UV radiation across a broad range of wavelengths and converting that energy into harmless heat. It’s remarkably efficient at this. The energy dissipates so quickly that very little is left over to cause chemical reactions in your cells.
But melanin has limits. Everyone’s skin contains a finite amount of it, and past a certain dose of UV, there simply isn’t enough pigment to absorb all the incoming radiation. The excess gets through to your DNA. Interestingly, melanin itself has a dual nature: under extreme UV exposure, it can actually participate in reactions that generate damaging molecules rather than neutralize them. This is one reason why no skin type is completely immune to UV damage, even though darker skin burns far less often.
Why Some People Burn Faster Than Others
How quickly you burn depends largely on how much melanin your skin produces. Dermatologists classify skin into six broad types based on its response to UV. People with very pale skin (Type I) are extremely sensitive, always burn, and never tan. Those with white skin that tans minimally (Type II) burn easily as well. Light brown skin (Type III) sometimes burns but can slowly develop a tan. Moderate brown skin (Type IV) rarely burns and tans readily. Dark brown skin (Type V) very rarely burns, and deeply pigmented skin (Type VI) essentially never does.
These differences come down to the amount, type, and distribution of melanin in the epidermis. People with lighter skin produce less melanin overall and a higher proportion of a lighter form of the pigment that offers less UV protection. But regardless of where you fall on this scale, UV still penetrates your skin and causes DNA damage. Tanning itself is actually evidence of injury: your body ramps up melanin production specifically because it detected UV damage and is trying to prevent more.
Why Your Skin Peels Afterward
Peeling is your body’s way of getting rid of cells too damaged to safely repair. When UV exposure crosses a certain threshold, skin cells initiate apoptosis, a form of programmed self-destruction. They do this because cells with severely damaged DNA are unstable and could potentially become cancerous if allowed to keep dividing. The cells essentially sacrifice themselves as a safety measure.
Once those cells die, your body pushes the next layer of healthy skin upward and sheds the dead layer. That’s the peeling you see a few days after a bad burn. It looks dramatic, but it’s a protective process. Cells that sustained minor damage can often repair their own DNA using built-in repair enzymes, so not every exposed cell dies. Only those beyond repair are eliminated.
Medications That Make You Burn Faster
Certain common medications lower your skin’s threshold for burning, sometimes dramatically. This is called photosensitivity, and it can cause sunburn-like reactions or rashes after surprisingly little sun exposure. The FDA lists several categories of drugs known to cause this effect:
- Common antibiotics, including doxycycline, tetracycline, and ciprofloxacin
- Anti-inflammatory painkillers like ibuprofen and naproxen
- Blood pressure and heart medications, particularly certain diuretics
- Cholesterol-lowering drugs in the statin family
- Oral contraceptives and estrogen therapy
- Acne medications containing retinoids like isotretinoin
- Some antihistamines, including diphenhydramine and cetirizine
- Alpha-hydroxy acids (AHAs) found in many skincare products
Phototoxicity, the more common form of this reaction, can develop within just a few hours of sun exposure. If you’re taking any of these medications and noticing that you burn more easily than expected, the drug is likely the reason.
Environments That Increase Your Exposure
Your surroundings can significantly amplify UV exposure without you realizing it. Fresh snow reflects about 85% of UV radiation, which means you’re essentially being hit from both above and below. Dry sand reflects around 17%, enough to accelerate burns at the beach even if you’re sitting under a partial shade. Water reflects about 5% under normal conditions, but that percentage climbs sharply at lower sun angles.
Altitude matters too. The atmosphere absorbs some UV, so the higher you go, the less filtering you get. A ski trip combines high altitude, snow reflection, and cold air that masks the sensation of burning, making it one of the most deceptive settings for severe sunburn. Similarly, overcast days still allow a substantial portion of UV through clouds, which is why people often burn when they don’t expect to.