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Have you tried oatmeal baths? This also relaxes you at the same time. If you don't have commercial oatmeal bath salts, you can make your own... it doesn't take much oatmeal. Tie it in a sock ---don't dump it into the bath water or you'll end up taking umpteen showers to get clean... and forever to clear the tub and drain lol

Put a 1/2 cup or less in a sock and tie it up... let it soak in the tub water for a few minutes and get in!!! It's worked for hives for ages... and allergic itches too...

And don't discount allergy too fast. Anything can cause an allergic reaction, and as your body ages, things change... including hormones and other chemicals your body produces. That it happens when you are stressed could mean it's a histamine type reaction, or adrenalin.

What does your MD say?