Or just scrub the helmet pads with washing up liquid and warm water. Or even better buy new pads, after realising quite how much ‘spring’ they lose I’ve started replacing mine every 6 months.
I’ve started keeping gym/cycling kit seperate from the general washing and putting a massive glug of dissinfectant (the strong pine smelling stuff you clean vomit off floors with) in with the usual powder. Reason, I was getting spots and occasional cysts (Ok acne is technicaly a cyst, but anything bigger than a baked bean deserves it’s own category) on my inner thigh and a few saddle sores which weren’t going away with sudocrem. The new routine seems to have stopped that. Just remember to set the machine to extra rinse otherwise I smell like a hospital!