Yoga releasing toxins?

I just started doing some very simple and basic hatha yoga exercises within the last few days and now around my neck and head and shoulders I feel as if I might get a rash - like my skin is sort of itchy. I have been especially concentrating on the chest expander and the shoulderstand because I had a lot of tension in my shoulders. Do you think that the yoga is causing toxins to be released into my bloodstream and causing problems? Thanks.