Helmet Cleaning?

Just wondering what is the best way to clean the inside of your helmet? If you go by the helmet manufactures guidlines you basically cant use anything. As recently Ive had an outbreak of pimples on my forehead (and yes I do wash! ) Just wondering has anyone else had this problem? I was think of just using a very weak mix of detergent with water?

Pretty easy if you have a removable liner. If not, fill up your bathtub with soap and water, or bubbles if you are then submerge the helmet sans the screen and scrub it with something like a washrag. Rinse it completely out of soap and let it dry out for a day or two. Good as new.