I have 3 helmutts which get cycled over a 2 wk period. Each goes into shower with me.
Oldest is about 5 yrs old and has gone thru a shower every 2wks for that entire time.
I have very salty sweat so lots of deposits - all get nice and clean in shower - I work the padding under water stream.
Squish the water out after shower and let air dry overnight.
oldest still have lots of life left.

I keep sun exposure to only the riding time...