Q: My 10-year-old loves to ride his bicycle, but he doesn't want to wear a helmet in the summer when it's hot. Does he really need it? He only rides on the sidewalk and is a very good rider.

A: Your son should wear his helmet whenever he rides. The helmet should be an approved bicycle helmet, fit snugly and be strapped on firmly.

We recommend that you make no compromises when such an important safety issue is involved. The fact that your son is a good rider and rides often increases rather than decreases his risk. The more time he spends on a bike, the more opportunity there is for a fall.

A bike helmet not only helps to protect the head in a crash between a bicycle and a car, it also absorbs much of the force when a child's head strikes a hard surface like concrete during a simple fall from a bike.

Imagine how damaging it might be for your son's brain if he and his bike fall on a sidewalk or curb!

Bike helmets have proven their worth. Children (and adults) wearing them are much less likely to injure their brains while biking. We suggest you make it a hard and fast year-round rule -- no helmet, no bike riding!

Talk with the other parents in your neighborhood. See if you can make a communitywide practice.

Dr. Wilson is director of general pediatrics at Johns Hopkins Children's Center; Dr. Joffe is director of adolescent medicine.