As someone from Britain with Scottish ancestry I don’t really tan at all. The melanin in my skin clumps in freckles, severely limiting its effectiveness at blocking UV. I can spend time outside in a t-shirt during the long summer evenings in Britain/Scandinavia but will burn during the midday sun. Living in California now the sun is stronger for longer so I just cover up.

San Francisco is at a southern European latitude. It’s a lot worse in the tropics.