How to get rid of skin allergy...my skin is red and highly itchy?

Not so easy: You don't tell us how old you are, if you take any medications or are exposed to the sun. This is a short list of possible causes. First aid - lukewarm baths, apply a comforting anti itch emollient such as sarna with pramoxime (otc) and take an antihstamine such as Cetirizine 10mg or fexofenadine 180mg. If these measures do not resolve the problem within a few days, see a physician.