There are two different mechanisms involved in the production of a tan by UV exposure. Firstly, UVA radiation creates oxidative stress, which in turn oxidizes existing melanin, leading to the rapid darkening of the melanin. UVA may also cause melanin to be redistributed (released from melanocytes where it is already stored), but its total quantity is unchanged. Skin darkening from UVA exposure does not lead to significantly increased production of melanin or protection against sunburn.[9] In the second process […]
The tan that is created by increased melanogenesis typically lasts for a few weeks or months, much longer than the tan that is caused by oxidation of existing melanin
People usually don’t claim to have a tan if they go back to their default skin color three days after their vacation ended, do they?
Yes, but if you read further it says:
People usually don’t claim to have a tan if they go back to their default skin color three days after their vacation ended, do they?