I've had problems with itchy skin since I was a teenager. In March of this year, I was diagnosed with Hashimoto Thyroid Disease. Since that time, my skin has itched all over - it's constant. Claritin and Benedryl do not help at all. I itch when take showers, excercise, go into an airconditioned room, after I bathe and shave; basically, everything makes me itch. I looked into the possibility of having chronic idiopathic urticaria, but I don't have hives. There is no redness - just itching all over. Is it possible that the thyroid condition has worsened my itching condition? My doctor put me on 7 days of prednisone, and I stopped itching for 7 days, but then it came right back. I have to keep my entire body covered up - can't expose the skin to heat or cold.
There is a (rather uncommon) condition called cold urticaria, or hives from cold. It isn't an allergy, just a tendency to get itchy or red on exposure to cold. You ought to see a doctor about it--an allergist or a dermatologist. Meantime, try taking Loratidine (over-the-counter Claritin) 10 mg per day. The extent to which you respond should help your doctor tell what is up.
Best.
Dr. Rockoff