I've suffered for years with prickly heat when holidaying abroad, and a friend recommended using a sun cream (suntan lotion) that doesn't contain any water. I found some in local cheapo stores, Poundstretcher and others, think the brand was called Malibu, smells of coconut anyway, and I tried it in Rhodes this year. After a few days I had no heat rash at all, and got really brave one day and went for a walk without a shirt on, in the midday sun...madness for me under normal circumstances....and had no bad reaction at all. I guess the oils I'd been using before contained water, which blocked the pores in my skin, causing the trouble. It works for me anyway. Good luck.