I'm not a doctor. This isn't medical advice. It's personal experience that I'm sharing. I hope that medical professionals will see it, though.
I noticed that I was getting the same kind of rash from sun exposure as the rash that I got after a fever.
The rash itself was really awful to endure, lasting several weeks and making life difficult. Interestingly, I found an effective anti-itching treatment that I have never heard of before: a warm salt-water sponge bath. This story is about a cure, though, and not just symptom treatment.
My last rash from sun exposure was after about an hour in the sun at a Florida beach wearing waterproof 45 SPF sunblock.
As a kid, I used to play in the sun quite a bit. I had a tan and could take sunlight well.
As an adult, I hadn't gotten exposure to the sun, except on my forearms, face, etc. I noticed that these areas (face, arms) were not affected by the rash.
I had been doing some weight training, where the body is stressed and then allowed to recover fully before trying it again. My trip to Florida was analogous to a sedentary person walking into a gym and trying to lift as much weight as possible — it's a good way to get hurt.
I guessed that I could gradually re-acquire my tolerance of sunlight through controlled, low-dose exposure to direct sunlight, with at least a week for recovery between exposures.
My first way for getting some sun exposure was to walk on a nearby railroad track with my shirt off, in shorts if possible, for about five minutes.
Later I began "laying out" for six minutes on each side: front and back.
Now I don't get rashes after fevers, and I doubt that a trip to Florida would cause a rash, either, especially if I tried to adapt to longer exposures.
I did just get a rash after a fever, for the first time in a long time, dispite the fact that I've been trying to get sun pretty regularly, and managing to get it maybe once every three weeks.
I went to the doctor, and he couldn't identify the cause of the condition, but he did prescribe a prednisone pack. This is a corticosteroid that I took in a decreasing dosage for six days. It totally cleared up my rash right away. This medication eliminated the whole ordeal.
I react pretty well to sun exposure now when engaging in outdoor recreation. I tan.