What to do for itchy rash?

Depends: It is difficult to guess what it may be given so little information. If the rash is confined to a small area, topical hydrocortisone may help. The most important step is finding the cause for the rash and thus you may consider consulting an allergist or dermatologist.

Depends on the cause: This rash would need to be examined, a history obtained & other tests may be necessary in order to diagnose this. Usually the lesions needs to be identified to determine the solution.

Depends on the cause: There are many types and causes of skin rashes that could cause itching. Several types of inflammatory conditions of the skin, allergic reactions, and sometimes bacterial, viral or fungal infections can cause rashes on the skin. Insect bites can also be the cause of a rash on the skin. Have it evaluated by a professional and get the appropriate treatment.