A sunburn is an inflammatory reaction in your skin caused by overexposure to ultraviolet (UV) radiation from the sun. It’s not just surface-level redness. What you see and feel on the outside reflects real damage happening at the cellular level, where UV rays alter your DNA and trigger your body’s damage-control systems. Most mild sunburns heal within a week, but the cellular injury they leave behind accumulates over a lifetime and raises your risk of skin cancer.
What Happens Inside Your Skin
Sunlight contains two types of UV radiation that reach your skin: UVA and UVB. They cause damage in different ways and at different depths.
UVB rays are absorbed mostly by your outermost skin layer, the epidermis. These rays are directly absorbed by your DNA, creating structural defects called pyrimidine dimers, which are essentially kinks in your genetic code. UVB is the primary driver of the visible redness and pain you associate with sunburn, and it’s also the wavelength most strongly linked to skin cancer development.
UVA rays penetrate deeper, reaching the dermis (the thicker layer beneath the surface). Rather than hitting DNA directly, UVA generates reactive oxygen species, unstable molecules that damage DNA, break down collagen and elastin fibers, and kill the cells responsible for maintaining your skin’s structure. This is why UVA is the bigger contributor to premature aging, wrinkles, and long-term skin damage, even though it plays a smaller role in the acute burn itself.
Both wavelengths trigger a cascade of inflammation. Your body detects the DNA damage, floods the area with blood (causing redness and heat), and releases signaling molecules that produce swelling and pain. This inflammatory response is your body attempting to clean up the damage and protect surrounding tissue.
Sunburn Cells and Why They Matter
One of the most important things your body does after UV exposure is kill off its own damaged cells. Skin cells with badly corrupted DNA are pushed into a self-destruct process called apoptosis, and pathologists can actually see these dying cells under a microscope. They’re called “sunburn cells.” This controlled demolition prevents cells with dangerous mutations from dividing and potentially becoming cancerous. It’s a protective mechanism, but it comes at a cost: enough cell death across a large area is what produces peeling, blistering, and raw skin.
First-Degree vs. Second-Degree Sunburn
Not all sunburns are the same. They’re classified by depth, similar to other burns.
A first-degree sunburn damages only the outer layer of skin. You’ll notice redness (on lighter skin), skin that feels hot or tight, tenderness, and possibly some swelling. After several days, the damaged skin peels off. On darker skin tones, a sunburn can be harder to see visually but still causes the same pain, tightness, and eventual peeling.
A second-degree sunburn reaches into the dermis. The hallmark sign is blisters. You may also see extremely red or wet-looking skin, white discoloration within the burn, significant swelling, and more intense pain. Second-degree sunburns carry real risks: when blisters pop, the open skin can lose fluids and electrolytes and become vulnerable to infection.
Severe Sunburn and Systemic Symptoms
When a sunburn is extensive or deep enough, it can affect your whole body, not just the skin. This is sometimes called “sun poisoning,” though it’s not actually a toxin. It’s your body’s systemic inflammatory response to widespread tissue damage.
Symptoms can include headache, nausea and vomiting, fever, chills or shivering, and dehydration. These signs indicate that the burn is serious enough to warrant medical attention, particularly if blisters cover a large area. Fluid loss through damaged skin can cause dangerous dehydration, and open blisters create entry points for bacterial infection.
Why Some People Burn Faster
The amount of UV exposure needed to produce a sunburn varies enormously from person to person. Dermatologists measure this as the “minimal erythemal dose,” or the smallest amount of UV that produces visible redness within a few hours. Your threshold depends largely on your skin type, classified on a scale from Type I (very fair, always burns, never tans) to Type VI (very dark, rarely burns). Fairer skin contains less melanin, the pigment that absorbs and scatters UV before it reaches vulnerable cells, so it burns with significantly less exposure.
A common belief is that you burn faster near water because of reflection off the surface. The reality is more mundane. Even under the most extreme midday sun, reflected UV from the ocean adds the equivalent of less than 1 UV Index point to your exposure. The real reason people burn at the beach or on the water is the absence of shade. There are no trees, no buildings, no awnings. You’re simply exposed for longer with no relief.
How Sunburn Heals
A mild first-degree sunburn typically resolves within three to five days. Redness and pain usually peak around 24 hours after exposure (not during the time you’re in the sun, which is why many people don’t realize they’re burning until it’s too late). Peeling begins a few days later as your body sheds the layer of dead and damaged cells.
Second-degree sunburns take longer, often one to two weeks or more, depending on the extent of blistering. During healing, the priority is keeping skin hydrated and protecting it from further UV exposure. Cool compresses, aloe vera gel, moisturizing lotion, and cool colloidal oatmeal baths can all help ease discomfort. Over-the-counter anti-inflammatory pain relievers reduce both pain and swelling. Staying well hydrated by drinking plenty of water helps your body manage fluid losses, especially if blistering is involved.
A few things to avoid: topical anesthetic creams can irritate burned skin. Corticosteroid creams, whether over-the-counter or prescription, have not been shown to help sunburns despite their use for other inflammatory skin conditions. If blisters rupture on their own, wash them gently with soap and water and cover them with moist gauze. Don’t pop intact blisters, as the overlying skin acts as a natural bandage.
Long-Term Cancer Risk
Every sunburn represents DNA damage that your repair systems may not fully correct. A comprehensive meta-analysis of 25 studies found that having been sunburned even once in childhood nearly doubles the risk of melanoma (odds ratio of 1.9). The risk increases with each additional burn, at every age.
For every five sunburns during childhood, melanoma risk rises by about 80%. Five sunburns during adolescence increase risk by roughly 66%. But adults aren’t off the hook. When researchers adjusted for the length of each life period, adult sunburns actually showed the strongest per-decade risk: five sunburns per decade in adulthood tripled melanoma risk. Blistering sunburns in adulthood carried the highest odds of all.
This means sunburn prevention isn’t just a childhood concern. The DNA damage from a bad burn at age 40 contributes to cancer risk just as meaningfully as one at age 10. The cumulative total matters, and each burn you prevent is damage your body doesn’t have to try to repair.