What Causes Skin Rash After A Hot Tub Bath?

I went in a friends hot tub about 3 days ago, and yesterday my friends was washing my hair with Batiste dry shampoo. My mum thought that she had held the can too close to my head, because while she was spraying it in my hair, it was very very cold, and we noticed i had lots of tiny, slightly itchy spots all around my neck reaching up to my ears. We checked it out with her mum (who is also a nurse, but i think she is a gyneacologist) and she said it was just a rash. I have had chickenpox when i was younger, and they dont itch all the time. Initially, my mum thought she had given me aerosol burn, but there were no spots on my scalp where my friend had sprayed the shampoo. When she looked at them again, she remembered that a few years ago after i went in a different friends hot tub i had these tiny spots. They arent anywhere else on my body, even though i was wearing a bikini. I also have random itchy spots and random times, that itch for a while, quite badly, before they go away again. I think i might be allergic to certain types of chlorine, because when i go to public swimming pools i never get rashes or anything from their pools or hot tubs. I was just a bit worried because we live in the UK and we are going on holiday to america next week, and i thought that if i had a skin condition or a disease of some kind, they wouldnt let me into the country. thanks in advance.