I have been using Nicoderm patch (21mg) for three weeks now with no real problems. I have just been putting it on my arm, then I read you should switch locations daily so I moved it to the side of my stomach. I broke out in a red itchy rash all over my whole body. I took Benadryl and it went away. The next day I put the patch on my arm and same thing happened. I took the patch off and took a shower and the rash went away. Tried again today with the patch on my arm and broke out in a rash. Is it possible to become allergic to the patch after 3 weeks with no problems?? I really don't want to stop using it because it has been working so well but I don't want this red itchy rash all over my whole body either.