Red itchy rashes that come on within minutes and go in hours, often rightly prompt people to consider allergy as a cause.
It is important to carefully consider the exposures that occurred before the rash appearing.
Sometimes if a rash keeps occurring it can be important to write down these potential exposures to help establish what are really causing the symptoms.
A Symptom/exposure diary can sometimes be helpful. Symptoms such as rash or swelling are recorded with the time they occur, and all potential exposures (foods, medications, activities), in the hours prior are also recorded.
This may help establish an allergic cause, but non-allergic rashes can also occur. These are best discussed with your doctor to consider the appropriate management.