take it from someone who knows. wear a helmet.

when I was young and dumb, I had an old Sony Walkman model 10 speed.
I was racing it down a hill once, without a helmet, going about 25MPH full blast down the street, when the chain snapped.
threw the chain right into the front wheel, where it turned sideways, and hit the fork, locking up the front whel, and twisting it into something resembling modern art.
I was thrown clear over the bike, and hit the street face first and slid, with the bike landing on top of me. I shredded the skin off one side of my face like I'd kissed a belt sander. I then got to stand up, and limp home with a 30 pound bike on the shoulder that wasn't skinned as well. Upon returning home, I looked in the mirror, pulled the flap of skin back over what was left of my right ear, and looked for some medical attention from my mother who thankfully is an RN.

A helmet would have saved my face. Thankfully the only scar I have from that learning experience is a small discoloration on my ear.. but the memory still lives strong, in my mind, now armored with a Garneau helmet.