Tanning quickly using 50 SFP
Here's a frustration: sunblocks do not seem to work. I have high melanin levels in my skin. Today, I was gardening for two hours in the afternoon sun. The ambient temp was around 20oC, but, yes, I was in full sun for the two hours, no hat, in a sheltered London garden. Before starting I slathered on SPF50 (full spectrum) from a in-date new bottle and I wore a long sleeved shirt. Taking a shower in the evening there was a clear dark tan line not there in the morning. My face was pinkish.
I get that we need to reapply regularly and sweating or exercise can reduce its efficacy. But neither of those should be the case. So, short of wearing a big hat and a scarf around the neck (which I do increasingly for much of the summer) what can be done and why should SPF on dark skin not work?
Any tanning is a sign of skin damage, even without burning. I have had radiotherapy and need to be careful on face, arms and upper body. I don't want any tan or skin damage. I am somewhat stumped.