Can I soak my helmet in water?
The helmet itself is (probably) polysterene foam inner and a harder plastic shell, it's fine to wash this in water and some mild detergent (eg dish soap)

You can try and wash the straps in hot soapy water.

The problem is the pads. Usually washing the pads means that they come unglued, the surface layers separate from the inner cushion part. All you can do is keep the extra ones you get to size a new helmet and swap them.

I don't know if pro racing type helmets come with multiple sets of replaceable straps and pads - but they should.