> The tan is caused by an increase in the activity and number of melanocytes, the cells that make the pigment melanin. Melanin helps block out damaging UV rays up to a point,
It's not particularly clearly worded but to me that seems to suggest that tanning increases melanin and that melanin helps prevent cancer regardless of whether your dark skin is natural or tanned.
But if tanning also produces cancer it remains to be determined which effect dominates (unlike for people with naturally dark skin, where the effect can only go in the beneficial sense).
Every source I've seen clearly states tanning always increases your chance of skin cancer. Tanning does provide a small amount of protection against burning (around 3 SPF worth), but no protection against cancer.
They studied based on 2 weeks of tanning which is very minimal.
You clearly get more than SPF 3 with a deep tan as you can spend 8 hours in direct sun without obvious problems. Without any tan you get a burn in under an hour suggesting ~SPF 10+.
Broadly, my understanding is that a major change in skin tone is 'worth' about 15 SPF, so tanning would fall somewhere below that.
For a fixed amount of sun exposure, spreading out the duration is better both to establish a tan and to allow more time for skin recovery. But there isn't really a case where tanning increases safety, because you get the tan via exposure.
It's like saying pilots who practice a lot are safer; for any given flight it might be true, but cumulative risk can only rise.
It's not particularly clearly worded but to me that seems to suggest that tanning increases melanin and that melanin helps prevent cancer regardless of whether your dark skin is natural or tanned.