Smelly Shoes? Help is at Hand
Health and Nutrition, May 2005.

Closed-toe shoes and boots thrust the feet's 250,000 sweat glands into overdrive. Normally, foot perspiration is odourless. But when sweat mixes with bacteria and starts to decompose - particularly in warm, moist, dark environments like shoes - foul smells and foot fungus can occur.

To kill these germs, spray a disinfectant such as Dettol on the insides, or saturate a tissue with medicated spirit and insert it overnight.

When possible, don't wear the same pair of shoes on consecutive days, and always let them air our before putting them on again ( especially important during the slushy months). If smells don't cease, consider scented insoles like Dr.Scholl's Odour Destroyers.