My cousin was using Retin-A and wasn't able to get into the sun at all. She said the doctor cautioned her very strongly about it and said she could do a lot of damage to her skin if she did.
A friend's husband is very sensitive to the sun. He cannot get out in it at all, not even with good sunblock. He's very prone to severe sunburn and just can't tolerate a lot of sun.
I have really thin, fine hair, and if I don't wear a hat, I'll get a sunburned scalp, which is no fun at all. I also have a place on my arm that I always put extra sunscreen on because I'm afraid it might react badly to the sun.