I wash mine in johnson baby shampoo - yes - the inner of the helmet in removeable. The outside i like to keep nice and shiny, polish it occassionally with a vigorous rubbing action ;0
the outside i use a very soft cloth with plain warm water, and buff it up,, the inside is ok because i wear a stretchy hat because of my mad hair, sometimes i put it outside visor open to get some fresh air,,
They say 'horses sweat, men perspire and women glow'. Well, I perspire like a horse, especially from my forehead (but my feet don't sweat at all, must be made upside down) so my helmet gets somewhat wiffy.
A man can't go through life with a wiffy helmet so I use muc off helmet foam sanitiser every otherday and take the lining out and wash it in soapy water using Wright's coal tar soap. It's then rinsed with the power shower and comes up smelling slightly clinical but very clean.
The outside I use hot water and couch roll.
Can't resist, nobody here cleans the inside of their helmet with an umbrella do they?