It is great that you have provided the details surrounding the development of your rash, as this makes it easier for us to diagnose the problem, or at least give you specific, useful information that will lead you towards a solution. Unfortunately, a skin rash is almost impossible to diagnose without actually looking at it, and in addition looking into the patient's medical history and various other details that could provide clues as to the origin of the rash. There are probably a hundred different types of rashes, caused by a hundred different diseases and medical conditions. Allergies and reactions to harsh substances are only two possibilities.
However these two are rather common possibilities and perhaps you should not rule them out completely. Allergies can sometimes develop quite suddenly, and many food allergies are to extremely common foods that are a regular part of most people's diet. Milk, eggs, wheat, and peanuts are among the most common food allergies. It is therefore advisable that you carefully keep track of what you eat in case the allergy returns. If it does return, you should try to notice whether there is a repeated link with something that you have eaten. Similarly, see if there is any link to any product that you use on your face, even if you have been using it for years (allergies can be to a variety of substances, not just food), or in fact anything that you came into contact with in the hours before the rash appeared.
If it turns out that an allergy is not the cause, you should visit a doctor; even after narrowing down the possibilities to conditions that cause a fine rash and a light itch, there is still a long list to go through.Hopefully the rash has gone away by now, but if it hasn't or it returns, the best thing to do till you know what it is to apply a cold compress using some ice.
answered by G M