This is a bit of a stupid question but what do you use to clean/sanitize your helmet?

sweaty hair and wind

I just usually rinse the straps and padding in warm water, while squashing the padding to work water in/out, then putting the helmet where it will dry quickly (usually above the water heater) so bacteria isn't encouraged to grow. Same goes for my gloves.

But if you really want it sanitized, you can do the above in a bucket with a mild bleach solution, say 1 oz. of bleach to 1 gal. water, and afterward rinse it really well.

Some people wash it in the shower.
I wash mine in the kitchen sink with dish soap and warm water. Then press the padding to get as much water out as possible. Then set it out on the patio in the hot sun to dry. Ready to wear again in no time.

My helmet got to smelling really bad. Someone suggested spraying it with alcohol to kill bacteria. I've been using Listerene in a spray bottle. Works surprisingly well. I just hope the alcohol doesn't harm the helmet.
I think the Listerene even repells bugs somewhat.

A lot of time the padding is velcro'd in, so you can take the padding out, wash it, and put it back in the helmet.

A helmet works by absorbing impact, though. I'm not expert and don't claim to be, all I'm saying is that subjecting it to chemicals or unusual stuff may or may not weaken the foam. I'm not sure - really, I'm not. Just a thought - don't know how the foam interacts with cleaning agents.

Sanitize?

No, actually it's easy. "Sanitize" just never occurred to me. I use any water-based (not solvent-based) commercial cleaner, like 409 or even Windex, or dish detergent in weak solution, on the outside. On the inside, I just run water and squish the pads until they're cleanish. Though now that think of it, that's more what I WOULD do if I cleaned my helmet, not what i actually DO.

No good reason to 'sanitize' or 'sterilize' a helmet. Just wash and rinse.
And then throw it in the dryer..............

Wearing a Headsweats-type headband or skullcap will keep it from getting quite so funky.

I just take it into the shower, shampoo and rinse the inside & hang it up to dry.
Sometimes place it in front of a fan to help speed the drying.

Ineteresting topic. I wash everything except the helmet and it's straps. The helmet smells badly when I have it on. I'll try few of the suggestions here.

I spray windex inside and on the straps, hose it to rinse then leave it on the backporch to dry in the sun.
Ernest

Vinegar and water in a spray bottle, the straps need a good scrub and the liners i just use soap and water.

Yes, turn padding side up in direct sunlight will kill many germs,virus & fungi like nothing else can. I also dust the inside of the helmet with Lysol disinfectant spray to start the germ killing process.