Sunburn's sting starts with damaged RNA, not damaged DNA
Sunburned skin hurts under a warm shower because inflammation resets its heat sensors: a receptor that normally fires at about 43 degrees starts firing at 29. Research has also shown the burn itself is set off by ultraviolet damage to messenger RNA, while DNA damage mainly drives the long-term risks.
Sunburn is a radiation burn. Most comes from UVB, since UVA carries less energy and is 1,000 to 2,000 times less effective at burning. When UVB damages messenger RNA, ribosomes raise the alarm through a protein called ZAK-alpha, acting like a cellular surveillance system. That triggers inflammatory signals and summons immune cells, producing the redness, heat and swelling. The damaged skin also repairs DNA, kills off hopeless cells, which later peel away, and ramps up melanin for future protection.
The timeline is deceptive. A burn can begin in under 15 minutes, yet signs may not appear for hours, and symptoms usually peak 24 to 36 hours later before easing after three to five days. Welding arcs can burn skin in seconds. Inflammatory chemicals called prostanoids and bradykinin lower the heat threshold of nerve receptors, and an overproduced protein called CXCL5 appears to activate the pain fibres.
Exposure varies with place and time. UV rises about 4 percent for every 305 metres of altitude, water, sand and snow reflect it, and clouds let a lot through. Arms and legs tolerate far more than the torso, neck and face, which burn two to four times as readily. There is a neat rule of thumb: equal shadow lengths mean equal UV, wherever you are, so the strongest dose comes at solar noon when shadows are shortest. Between the 1970s and the 2000s, thinning ozone raised average surface UV by roughly 4 percent.
Susceptibility differs widely. The six Fitzpatrick skin types run from pale skin that always burns to dark brown skin that rarely does, though every type can burn. Young children and people over sixty are more sensitive, some medicines heighten reactions, and rare conditions such as xeroderma pigmentosum impair DNA repair. Lifetime burns also add up, since melanoma risk climbs with the number of episodes.
Source: Sunburn
