If your blood is very toxic, it could be that practicing an inverted pose in particular (shoulderstand) would cause toxins to exit in a different manner, ie. rash-like thing. This doesn't mean you should discontinue yoga, but perhaps consider some of the cleansing protocols mentioned on this site. Most particularly bowel and liver cleansing. Ideally you don't want to release toxins through the skin but through the regular channels of elimination, however if these are too congested the toxins move to the bloodstream and then find new and exciting ways to exit....or not!
I'm not sure what the "chest expander" is...cobra?