I always wear a helmet but I found they're not as effective when you land on your face at 20mph. I woke up to an EMT asking how many fingers (had to struggle to resist my sense of humor, it was still there...) That was a trip to the trauma center, concussion, broken tooth and loads of cuts and abrasions. But apparently after the face plant I flipped, cracking the back of the head - the helmet did its job there, it was deformed in the rear. And my forehead was undamaged. It was a bad experience but could have been worse and I recovered quickly.