What a sunburn does to your skin and how to care for it

What happens in skin cells during a sunburn, how to treat one at home, when to get medical care, and what past burns mean for skin cancer risk.

A sunburn is a radiation burn. Ultraviolet (UV) light from the sun or a tanning bed damages the DNA inside skin cells, and the redness, heat, and soreness that follow are the body's response to that injury.

What happens inside the skin

UVB, the shorter and more energetic part of the sun's UV, does most of the burning. The epidermis, the thin outer layer of skin, absorbs the bulk of it. UVA travels deeper, into the dermis, the thicker layer under the surface, and adds to the damage.

When UV energy hits a skin cell, it can distort the DNA code. Cells carry repair tools for this, and they fix most of the errors. A cell with more damage than it can repair shuts itself down through a programmed process called apoptosis. Pathologists can see these dying cells under the microscope and call them sunburn cells.

Injured cells also send out chemical alarm signals, including prostaglandins and proteins called cytokines. The signals widen blood vessels in the skin and draw in immune cells. Extra blood flow produces the redness and warmth. Fluid leaking out of those vessels produces swelling and, in a deeper burn, blisters.

Why the burn shows up hours later

Sunburn runs on a delay. Redness usually appears 2 to 6 hours after the exposure and keeps building until it reaches its worst at about 12 to 24 hours. The skin can look normal while the damage is happening, which explains why so many people stay out too long.

Pain tends to be strongest between 6 and 48 hours. A mild burn settles in 3 to 7 days. A blistering burn often needs 7 to 10 days to heal.

Why the skin peels

Peeling usually starts 4 to 7 days after the burn. The sheets that come off are made of cells too damaged to keep, and shedding them is how the body clears them out.

Let the skin come off on its own schedule. Pulling at it uncovers new skin before that skin is ready and raises the chance of infection. A plain moisturizer eases the itch.

First aid that helps

1. Get out of the sun as soon as you notice pink skin or a tight, hot feeling. Go indoors if you can.
2. Cool the skin with a cool shower, a bath, or damp cloths. Avoid putting ice directly on a burn. Pat dry gently and leave the skin slightly damp.
3. Apply moisturizer while the skin is still damp, and reapply as often as you like. The American Academy of Dermatology suggests products with aloe vera or soy. Skip sprays and creams that contain benzocaine or lidocaine, which can irritate burned skin.
4. Consider an over-the-counter anti-inflammatory pain reliever such as ibuprofen, if you are able to take that type of medicine. It eases both pain and swelling.
5. Drink extra water for the next few days. A burn pulls fluid toward the skin surface and away from the rest of the body.
6. Leave blisters alone. The roof of a blister works as a natural bandage over raw skin. If one opens by itself, keep the area clean and cover it with petroleum jelly.
7. Keep burned skin fully covered with loose, tightly woven clothing whenever you go outside until it heals.

Burns that need medical care

Most sunburns heal at home. Some become a medical problem, either because a large area of skin is injured or because dehydration and heat illness arrived along with the burn. Call a doctor or go to urgent care for any of these:

• Blisters that cover a large part of the body, or blisters that are very painful
• Fever or chills
• Dizziness, fainting, or confusion
• Nausea, a fast pulse, or fast breathing
• Signs of dehydration, such as extreme thirst or passing very little urine
• Signs of infection, such as red streaks, pus, or pain that gets worse after the first 2 days
• Eye pain or strong sensitivity to light

Babies are a separate case. Their skin burns quickly and they lose fluid fast. The Skin Cancer Foundation advises calling the doctor right away for any sunburn in a baby younger than 1 year, and keeping babies under 6 months out of direct sun altogether.

What a history of sunburns means for skin cancer risk

The redness fades within a week. Some of the DNA damage stays. A cell that survives with unrepaired errors passes them to every cell it produces, and errors in the genes that control cell growth can pile up over decades. Skin cancer grows out of that slow pile-up.

Studies of large groups put numbers on this. According to the American Academy of Dermatology, having 5 or more blistering sunburns between ages 15 and 20 raises melanoma risk by 80% and raises the risk of nonmelanoma skin cancer (basal cell and squamous cell carcinoma) by 68%. The Skin Cancer Foundation reports that Having 5 or more sunburns over a lifetime more than doubles the risk of melanoma.

These figures describe groups of people and cannot predict what will happen to one person. Many people who burned badly as teenagers never develop melanoma.

Past burns can't be erased, but they are useful information. Tell your doctor or dermatologist about blistering burns in childhood or the teen years, tanning bed use, and any years spent working outdoors. Doctors use that history, together with skin type, mole count, and family history, to decide how often a full skin exam makes sense. UV damage keeps adding up at every age, so sun protection started at 40 or 60 still lowers the total dose your skin receives.