Sudden rashes appearing on the skin after giving pressure is also called as cholinergic urticaria. This is called as pressure urticarial also. This is because certain cholinergic are released in the body after a certain pressure is given to the skin. There is no exact treatment for this. Just some anti-allergens and some immunosuppressants, but they have their own side effects. So you have to consult your dermatologist. They will judge and give you accordingly. As such there is nothing to be done.
