Hi.. Thanks for the query.. The symptoms of red rashes over the arms and hands that was initially itchy and has now broken out severely seems to be due to allergic reaction only.. However it looks competent with poison ivy/oak, but such symptoms can be due to other common allergens like any foods or medications, surface irritants like any detergants, soaps and toxin/ chemical exposure to skin, leather, latex, any poisonous insect bites etc.. So my suggestion is to consult an Emergency room and get a blood test done to rule out the exact cause of the reaction.. Meanwhile you can continue taking anti allergics like benadryl and apply steroid ointment over the rashes.. You can also get a steroid shot for faster relief.. You can do cool compresses over the skin to reduce irritation and itching.. You can apply Calamine lotion to soothe the skin.. Avoid scratching over the rashes if it itches as there can be spread of infection.. Hope this helps.. Regards.