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Peroxide is a strong oxidizing agent! Your razor will not be the same color when you finish with this procedure... use at your own [tremendous] risk.

It really depends on what the scales are- I think it would be quite a gamble. Unless you are rubbing the scales all over open wounds, however, I wouldn't worry about it.

If you want to sterilize a second hand blade, I highly recommend Barbicide... inexpensive, professional, kills EVERYTHING. Just soak the blade for 10 mins, rinse, dry, and it's sterile.

Alcohol will be fine on the blade, but it might oxidize some hard-rubber scales. I'd test it on a small spot before doing the whole thing.