One single severe sunburn during childhood (or later) is sufficient to develop a bad case of melanoma (bad guy skin cancer) thirty or forty years later. One. single. severe. sunburn.
One day, you are wondering about that constantly itching mole that has grown lately and lost all symmetry for that matter (and did you see a trace of blood the other day ?), but only your mother remembers that one day — 34 years earlier — when you sunburned so badly in Spain that a square foot of skin peeled off of your little belly in the Aftermath.
One. single. severe. sunburn. is. enough.
But changing moles tell a story, and as soon as you notice your skin going berserk — even on a tiny scale (“honey, your rectangular micro-mole isn’t rectangular anymore”), you have to make an appointment with a dermatologist for a complete check-up as soon as you can.
A very good friend of mine waited (way) too long to consult a doctor, and basically walked around with a lump the size of a grapefruit on one of her legs. The tanning in her 20s and 30s had done the damage, and now — in her late 60s — she would finally receive a diagnosis after decades of ignoring medical warnings every which way.
The magical thing about noticing skin cancer is that it hardly boils down to hard core Medicine in the end. It becomes a mathematical game —
About noticing a-symmetry, after that very first sunburn.