My Shoei (XR800?) was getting bit on the pongy side. No mushrooms yet, but definitely on the wrong side of "pleasant". Time for a clean, methought. So, I got a little aerosol tinny of Carburol Helmet Sanitiser, and guess what? It does exactly what it says on the tin.
One application: spray on, foams up, wipe off, leave to dry. Very nice and fresh (smells peachy). But the amazing thing (to my simple little mind anyway!) is that all the padding has been rejuvinated. The helmet is snug, tight, very comfortable, and probably fits tighter and better than it did when new.
I would HIGHLY recommend this Carburol stuff!