In spite of all the hoo-hah about helmets, you can wear a helmet but it still won't protect you well unless 1) it's fitted properly; and 2) you wear it correctly.

Fit is key. Buy the smallest-sized helmet that fits your head. (And yes, though they are actually the same company, Bell and Giro helmets fit differently. Bells tend to fit "round" heads better, Giros fit better if your head is more oval.) Use the adjustments in the pads and straps to make sure the helmet fits snugly on your head, without wiggling or bouncing around. You want the foam in the helmet to take the lick and cushion your head, not the double-strike of your head impacting the foam in a loose helmet. That's what the extra pads are for... some of the less expensive helmets are cast in a single one-size-fits-most form, and they use the extra padding to fill in the gaps between your helmet and your head.

A helmet has to be worn properly in order to protect you. Wear it square and level on the head -- not cocked back, tipped forward, or otherwise cock-eyed. You should be able to fit the width of two fingers between the helmet and your eyebrows. Adjust the chin straps so that they form a "V" around your ears, with the little clip securing them just below your ear lobe. The chin strap should be fastened and snug, enough that you can just slip a finger between the strap and your chin. It shouldn't be hanging loose under your chin or down around your adam's apple.

I've seen poorly fitted helmets (loose chin strap, worn cocked back on the head) simply peel away from the head in an over-the-handlebars crash. The fellow had his helmet checked pre-ride, but along the road it "felt tight" so he loosened the strap and tilted it back. A little later he touched wheels with the rider in front and went over the bars to the pavement. The helmet hit first, and since the straps were loose, rolled right on back exposing the rider's forehead to the street. Fifteen stitches, a grade 3 concussion, and a ride to the ER 20 miles away in an ambulance, coupled with 48 hours in the hospital for observation. $$$$$!

Same circumstance, but with a properly fitted and worn helmet, a young lady went over the bars and landed smack on the front of the helmet. This time the foam did its job, crushing a 4" circle pert near flat. The young lady was a little stunned, and had a scrape on her right chin and knee, but was otherwise okay. Had she not been wearing that skid lid, we'd have had a funeral for sure.

Helmets are good things, but you've got to fit them and wear them right, and rememer that they actually are the last layer in a scheme of protection, not a magic wand against mishap or injury.