The freezing point will vary because of different substances in different shampoos that will react differently together.
Shampoo will freeze when put in ice, but your shower can only produce two temperatures which are cold (not ice) and hot (also not ice), so you do not have to worry about shampoo in your shower.
Heck yes you can! it gets those buggers right out of there!
My favorite clarifying shampoo that I always recommend to clients is Paul Mitchell's Shampoo 3.
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