If you have no idea where your instructions are, what then?

• You can check the manufacturer's Web site.

• The usual instructions for cleaning a helmet call for washing it in mild soap and water, rinsing thoroughly, and air drying. We normally use a few drops of dishwashing liquid in a bucket of water and a sponge.

• Some fastidious riders take their helmet into the shower with them after every ride and wash it there.

• Bicycle helmet tests for most standards use one wet sample, immersed for at least four hours before the wet test. So you know that the helmet can be immersed in water and still perform. But do not leave it immersed for long periods of time, since the materials will absorb some water, and that may affect the adhesives used in construction. In addition, foam saturated in water usually gives a harder landing on flat surfaces.

• Never use solvents or harsh cleaning materials on your helmet, since some of them may attack the foam or the shell and weaken the helmet. Gasoline, for example, dissolves EPS foam so well that in some developing countries the resulting gunk is used as glue. We did a test of many commonly used consumer products for helmet damage and found that most of them did not cause performance degredation despite some visible effects.

• Never put your helmet in a washing machine, dryer, microwave or dishwasher to clean it! We have a page on our testing in dishwashers.

• If you are concerned that someone who has worn your helmet may have had head lice, put the helmet in a plastic bag for two weeks until any nits left behind have hatched and died. See the cleaning products below or our page on lice for more solutions.

Do not put your helmet in a dishwasher

Cleaning Products

• Progold Helmet Cleaner and Deodorizer comes from a supplier of chain lubes and other bike products. Comes in a spray can. It foams on contact, and you are supposed to wipe it off after a minute, then wipe again with a damp towel. Available in bike shops, where retail is $10 for an 8 oz. can. The cautions: "Use in an area with adequate ventilation. High vapor concentrations can be irritating to the eyes and cause headaches or dizziness...Do not spray near open flames or sparks...Do not expose to heat or store at temperatures above 120 degrees F (49 degrees C)." That means you can't carry it in your car in the summer. It has a pleasantly mild floral/citrus masking scent, with chemical overtones.

• Charles Owen Hat Cleaner and Charles Owen Hat Deodorizer both products come from an equestrian helmet manufacturer and are sold by suppliers of equestrian products. They are for helmets despite the use of "hat" in the name. The cleaner is a foam product. It foams when you spray it on, and you wipe it off after a minute. Both products have good web reviews.

• Bennett Engineering Helmet Fresh If your helmet has gone sour (a problem usually affecting motorcycle or BMX helmets with full liners), Bennett Engineering makes this product to eliminate helmet odor. We have not used it on a sour helmet, but were pleased to find that it has no masking fragrance, just a faintly medicinal or bleach odor. Cycle World said "After kneading the clear fluid into the liner, we left it to air dry. Once it had dried, the helmet didn't smell like new, or even like cheap perfume. In fact, it didn't smell at all." Other reviews on the Web support that. Motorcycle stores and Web sites have it, including Bell (motorcycle) Helmets and Simpson. A four ounce spray bottle runs about $5.