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My daughter suffers terribly to the point where on holiday a few years ago we had to take her to the hotel doctor. They gave her an injection of antihistamine into her bottom and she was fine from then onwards but obviously no one wants to have to face that every year. When I asked if there was any way to avoid it in future he suggested taking a one a day non drowsy antihistamine every day for two weeks before the holiday and every day of the holiday. We've done it for the last three years and she's been fine. No prickly heat or rash at all and that's in 35 degrees or more in Greece. The tablets aren't expensive so I'd suggest giving it a try.