Humans are allergic to "stuff" - all kinds of stuff.
We can be allergic to things that we ingest (food and drugs), things that we breathe, and things that we touch, and very often the allergic reaction will manifest itself as a skin rash.
Allergic reactions to food that manifest as a skin rash are not at all uncommon.
As a matter of fact, a skin rash is most often the result of an allergic reaction to a food.
There are many ways that the human body can react to a food to which it is allergic.
The tongue can swell, breathing can become difficult...
all sorts of things.
The most minor way, however, and the most common, is that a skin rash will develop.
The "treatment" is simply to avoid the food that caused the rash.
Topical ointments may be applied to relieve the itch, but once the guilty food has passed through the digestive system, the rash will clear up on its own.
Drugs can also cause skin rashes when a person is allergic to the drug.
Warnings that are handed out with every prescription will tell you if a rash is a possible side effect and if you need to contact your doctor.
Over-the-counter medications have warnings on the label.
Pollutants in the air can also cause skin rashes.
These are not as easily identified as other allergic skin rashes and are not as frequent as skin rashes that are caused by food, drugs, or contact.
There are many people who will develop a skin rash when they come into physical contact with such things as metal (particularly nickel), certain plants (poison oak or poison ivy), or chemicals (household cleaning products).
Avoiding contact is the best prevention measure, and itching can be controlled with a topical ointment until the rash clears up.