Sunburn is a fat going rancid inside you, and the compound it produces has a name.
4-hydroxynonenal. An aldehyde. Measurable, published, sitting in the literature for forty years.
It does not come from nowhere. It is a breakdown product of omega-6.
Specifically linoleic acid and the arachidonic acid your body makes from it.
Linoleic acid has two double bonds. Every double bond is a weak point where oxygen gets in.
Saturated fat has none. Monounsaturated has one and it is hard to reach.
Your cell membranes are built from whatever fat you have been eating, on a turnover of roughly two years.
Ultraviolet light hits the skin and strips a hydrogen off one of those weak points.
That starts a chain reaction called lipid peroxidation, and a chain reaction does not need more light to continue. It propagates on its own.
The chain breaks the fatty acid apart. Out come 4-hydroxynonenal and malondialdehyde.
Those aldehydes cross-link proteins, damage DNA and trigger the inflammatory cascade.
The redness, the heat, the swelling, the peeling. That is the immune response to the wreckage, not the sunlight itself.
More linoleic acid in the membrane means more fuel in the fire.
Linoleic acid in American body fat ran at about 9 per cent in 1959 and reached 21 per cent by 2008.
Your grandfather worked outdoors all day in a vest and came home brown, on membranes built from lard, butter and dripping.
He was less flammable, and nobody had told him he was doing anything brave.
Four grams of omega-3 a day let volunteers take 36 per cent more UV before burning. Fish oil cut the inflammatory signal in irradiated human skin by more than 60 per cent.
Sunlight is not the accelerant. It is the ignition.
Fifty years of advice about what to spread on your skin, and not one word about what you built it out of.
Interesting that you mention 2 years.
I have eaten carnivore 2 1/2 years and have gone from “sun sensitive” to walking and working outdoors at altitude with shirt off and having no issues.
We started annual trips to Maui about 12 years ago, going in winter when summer tan had faded. I burned every first day for 6-8 years. We cut seed oils about 4 years ago and the past two trips have been almost entirely burn free. Still use sunblock on the trips, not nearly as much.
Mass sunbathing arrived in the 1920s and the melanoma curve did not go vertical until the 1980s, and nobody has ever explained the sixty years in between.
For most of Western history a tan marked you as a labourer. The gentry stayed pale on purpose and carried parasols to prove it.
Then it flipped.
The 1920s make brown fashionable. The Riviera season, the swimming costume, the deliberate lie in the sun.
The 1930s build the lidos. Every British town gets an open air pool and the country strips off in public for the first time.
1938: the Holidays with Pay Act puts working families on a beach.
The 1950s and 60s send millions of pale northern Europeans to the Mediterranean for a fortnight of maximum exposure, twice the price and half the clothing.
So the exposure change is finished by the middle of the century.
The curve waits another thirty years, in a cancer that supposedly has one cause and one only.
Set the other timeline against it.
Crisco arrives in 1911. Margarine takes the wartime kitchen. Soybean oil goes from a rounding error in 1909 to the largest single source of fat in the American diet.
1961: the American Heart Association tells the population to swap saturated fat for polyunsaturated, and the population does it.
Body fat turns over on a half life of about two years, so a change in the national oil supply takes a generation to finish rebuilding everybody in it.
One timeline is sixty years early. The other lands on the curve.
The lifeguards of 1935 should have been the first to go, and they were the last generation this barely happened to.
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