Speaking as someone who has been sunburned more times than they should have in the past, what you really need to relieve the pain is a slightly over-ripe tomato. Slice it, and gently rub the inside of it onto the sunburned area. This will relieve it faster and more effectively than any moisturiser on the market.
The other thing you should do is religiously avoid getting sunburned in the future. The human body uses a helluva lot more water when you are sunburned (again, I know), and consequently, the risk of dehydration increases dramatically.
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I am clinically insane. I am proud of it.
That is all.