skin grows/regenerates at a rapid pace, which means mutations (mistakes in DNA replication) are naturally likely to happen there than in slow-growing tissue. skin cells and the immune system are constantly self-surveying and nipping these in the buds, under normal conditions. but there are things that can affect this process.

a recent study of 2 million people in ontario showed that both high-sun and low-sun exposed people had higher risk of melanoma than people with moderate exposure.

https://www.nature.com/articles/s41598-026-48477-4

https://imgur.com/a/site-specific-melanoma-risk-by-occupatio...

a possible explanation is that UV light stimulates repair pathways within the skin, which boosts the baseline level of repair.

Enhancement of UVB-induced DNA damage repair after a chronic low-dose UVB pre-stimulation

https://www.sciencedirect.com/science/article/abs/pii/S15687...

another explanation is that as much as you can try to cover up, occasionally you may slip up, and going from extreme low-exposure to intense sun is especially bad, because your repair pathways are not primed, skin is untanned, etc..

in conclusion, extreme low or high sun exposure is bad. at the beginning of the summer you should gradually exposure yourself, and then exposure yourself daily but not overly, for the rest of the year.

There's also the effect that sunscreen makes you spend more time in the sun than if you didn't use sunscreen because you think you're "protected".