I get this rash (Photo) usually when i become hot, flushed, embarrassed. In situations such as one on one talks with my boss or whenever I get single out in a team meeting. It also comes whenever i eat hot food. I don't have any allergies to my knowledge.
Any help would be appreciated.
Possibly a histamine rash. Its your body reacting to all those stimuli you have mentioned. Its quite common and shouldnt last. You can see this sort of rash on the necks of people being interviewed on TV,when they are stressed by the situation.
Try to keep cool,and only wear 100% cotton clothing. Only have cool showers,not hot baths. You can also try taking a simple antihistamine like cetrizine ,if it really bothers you, which you can buy at any chemist/pharmacy/ supermarket,but often its not necessary.