What is the cause of my itchy rash?

Itchy rash: Many answers apply to your question and it is best answered by a thorough history and physical exam. See your doctor about it and they may decide if you need to see a specialist.

Many possibilities: There are many things that could cause the skin to itch. Several types of inflammatory conditions of the skin, allergic reactions, sun exposure, insect bites, and sometimes bacterial, viral or fungal infections can cause rashes on the skin. Have it evaluated by a professional and get the appropriate treatment.

Many causes: You don't describe y our rash, so the answer has to be "generic". Rashes can be due to unknown causes; insect bites; allergy to foods, plants, pollen; irritation by chemicals and clothes; medications; sun light; cold; cold water; heat; vibrations; some skin diseases. Rashes that last longer than six weeks are considered chronic and in many cases we don't find a cause.