My friend has through this year had 5 freak allergic reactions. her entire body especially back, back legs and under arms, gets rash like as if ivy or something. she gets very hot and the only common denominator seems to be dust. what could this be?

This could be time: Time to find a thorough allergist and an equally thorough dermatologist. One's primary care doctor can help, too. In such a case, a helpful thing to do is to make a diary on a calendar, starting from about 2-3 months before the first symptoms occurred, and continuing until now. Record activities, travels, foods, medications, pets, cosmetics, other illnesses, etc... and show the doctors the diary.