No harm done bhg481.
Over the years, I've come across lots of people who believe that the phenomenon is due to hydrogen sulphide production. No doubt it links in with the common name for hydrogen sulphide which is "rotten-egg gas".
Takes me back to my schooldays of making the gas with my chemistry sets and being exiled to the shed by my parents. The fun we had breaking those glass vial "stink bombs" bought in the toyshop underfoot in the classroom - cleared the classroom in no time at all lol. I've always had a great fondness for hydrogen sulphide.