Hi L and S - I get that if there are open wounds that you would be unable to give blood - but am not sure about old healed wounds. I have given blood in the past, but my scars would be seen if I gave it now - so I too would be interested in the answer to that question. I am also aware that the last time I did give blood it gave me the same relief that SI does and for that reasons too I have been avoiding it as I think that maybe for me giving blood is a sort of SI thing and not a good thing.