My helmet actually gets more stinky in the winter when its more humid and less hot to dry it out overnight. But it also gets stinky in the so called 'monsoon' season we have here, with a bit higher humidities, which is about now.

I like to take out pads and hand wash them thoughoughly in dishsoap. Also wash the helmet in sink with dishsoap. Lay it out in full sun to dry. A quick very light spritz of some alcohol based deoderant (or purfume) on the inside helps too. Not much as you don't want to damage helmet. Seems to get rid of the stink - main thing you want to do is kill the bacteria which sun and alcohol can do.

Al