I just returned from short trip in wich time I stayed in a hotel. After returning an itchy dry rash has appeared on my arms. What could b the cause?

Rash. This is likely a contact dermatitis from exposure to unfamiliar soap or detergent/fabric softener in the bedding. Try otc moisturizer 2 to 3 times per day as well as otc Hydrocortisone cream 2 to 3 times per day. If the rash persists, see your doctor.