Head injuries cause 75% of our 500+ annual bicycle deaths.
If your helmet does not have a CPSC sticker then don't use it for bike riding. In 1998, the Consumer Product Safety Commission updated the rules and regulations for bicycle helmet standards, including impact resistance. You can read the PDF file here: http://www.bhsi.org/cpscstd.pdf - courtesy Bicycle Helmet Safety Institute. You can also visit the official federal agency website www.cpsc.gov

Aside from the bicycle, a helmet is the only other absolutely indispensable part of riding a bike. The helmet is designed to protect your head. If you hit the ground, the likelihood if your head hits the ground is that you’ll get a concussion, serious injury, or perhaps get killed. A helmet is designed to put something between you and whatever it is you hit. The choice of wearing a bicycle helmet can mean the difference between life and death.
Medical research shows that bike helmets can prevent 85% of cyclists' head injuries. And helmets may be required by law in your area."
From young children to adults, protecting your noggin should be a priority! Throughout the years bicycle helmets have come a long way in protection since leather straps and EPS foam. According to the Bicycle Helmet Safety Institute (2006).
Helmets, such as the protec helmets are designed of hard plastic; inside they have padding. When you buy a helmet, you make sure it’s one that’s snug but not too tight on your head. Helmet straps; the purpose of the strap is to keep your helmet on you when you’re falling or otherwise off the bike and on your way to the ground. It should be tightened. The straps should tightened so you can get no more than two fingers between your chin and the strap. Helmets are adjustable.