How to Treat a Severe Sunburn: An Evidence-Based Timeline
The first 24 hours matter most. Cooling, hydrating, and pain management for moderate to severe sunburn — and when to go to an ER.
Sunburn is a delayed-onset burn injury. Redness peaks 12 to 24 hours after exposure, and inflammation continues for three to five days. What you do in the first hours meaningfully changes how bad the burn feels and how it heals.
The first hour
Get out of the sun. Cool the skin with a lukewarm shower or a cool damp towel — not ice, which can extend the injury. Take ibuprofen or naproxen immediately; NSAIDs blunt the prostaglandin cascade driving the burn and are most effective when taken early.
The first 24 hours
Hydrate aggressively — burned skin pulls fluid to the surface. Fragrance-free moisturizer with ceramides or aloe vera gel reduces discomfort. Avoid petroleum jelly, which traps heat. Skip retinoids, exfoliants, and waxing for at least a week.
Signs you need medical care
Blistering over more than 20 percent of the body
Fever, chills, or nausea
Confusion or dizziness (possible heatstroke)
Severe pain not managed by OTC medication
Signs of infection: yellow discharge, expanding redness, red streaks
The healing window
Peeling starts around day three to seven. Do not pick — you can extend hyperpigmentation. Keep the area moisturized and out of the sun until fully healed, then use SPF 50 on the site for the next month because new skin sunburns fast.
Key takeaways
Cool, hydrate, ibuprofen early.
Blistering over 20 percent BSA or fever means ER.
Protect healed skin from sun for a month afterward.
Using How to Treat a Severe Sunburn: An Evidence-Based Timeline in practice
UV strength on this page follows solar elevation, ozone thickness, cloud cover, altitude, and surface reflection. Snow can bounce back most of the UV that hits it, water and sand far less, but all of them add to the dose skin receives.
Burn-time figures come from minimal erythemal dose (MED) values published for each Fitzpatrick skin type, divided by the erythemal irradiance at a given UV index. Personal MED varies by roughly 20 percent, so treat every number as a planning range.
Reapplication matters more than the SPF number. Reapply roughly every two hours outdoors and immediately after swimming, heavy sweating, or towelling, regardless of what the bottle claims.
Cumulative dose drives photoaging and long-term skin damage more than any single day. Small daily exposures on commutes, walks, and driving add up across a season.
Plan outdoor blocks around the peak UV window, usually between 10am and 4pm local time. Shade, UPF fabric, a wide-brim hat, and UV-blocking sunglasses reduce dose more reliably than sunscreen alone.
UV scale reference
The WHO scale groups UV 1-2 as low, 3-5 as moderate, 6-7 as high, 8-10 as very high, and 11 or above as extreme. Protection is recommended from UV 3 upward, and shade during the middle of the day becomes the priority from UV 8 upward.
A practical routine at moderate-to-high UV is roughly one ounce of broad-spectrum sunscreen for full-body coverage, applied 15 minutes before going out, then reapplied on schedule. Clothing, hats, and shade carry the rest of the load, especially for children and anyone with a history of easy burning.
Keep exploring DermUV
These pages give more depth around how to treat a severe sunburn: an evidence-based timeline, from UV-scale reference material to calculators and city forecasts.