Cracks in my Helmet
Summary: Cracks in a helmet indicate damage or deterioration. Your protection is compromised. In all cases you will want to replace the helmet now.
The question: I have cracks in my helmet. What should I do?
The answer is clear: replace it!
Large cracks are normally caused by impacts. They indicate that the foam beneath has been partially crushed to save your brain. Unless you have a multi-impact foam, it does not recover, and would not be fully protective in another fall. Replace the helmet and be glad.
A second type of crack is the small single crack or multiple cracks that can develop in the shell without major impact damage. Sometimes focal impacts that are not really destructive to the helmet can cause a small, sharp deformation to the outer shell of a helmet, resulting in tiny hairline cracks that are similar to "crazing." In thicker plastics, crazing may be only a surface effect, but in thin helmet shells it is likely to go all the way through. Depending on the material of the shell, this localized cracking may be more likely to occur as the plastic ages, or after repeated temperature cycling. Hot car trunks and interiors can accelerate the process.
The primary function of a thin shell on a helmet is to hold it together in a bad impact (with a car) so that it is there for the second impact, with the street. Other than that, if you have a less expensive helmet with a taped-on shell the thin shell probably does not make much difference in energy management, so minor defects in the shell may not indicate reduced performance for a single impact. But in a high end helmet with very large vents and less foam, the shell actually helps hold the helmet together in the first impact, particularly with an impact on a projection of some sort. In that case, the helmet can fail if the shell is cracked because the structural strength is compromised. Cracks in any type of shell may be a sign of increased brittleness, potentially increasing the possibility of further cracking that could cause lacerations if the cracked shell comes into contact with skin. So whether or not the tiny cracks impair the functionality of the helmet, they can be a source of problems unrelated to impact protection. It is unlikely that you can repair that kind of damage. You have to replace the helmet.
A few shells are made of clear plastic that is painted on the inside. If you have one of those, the cracks might be only in the paint, in which case it may be only a cosmetic problem. But the odds are very small that you have one of those helmets. You should be able to confirm that by running your fingernail across the crack. If it catches, the shell is cracked, not just the paint underneath. And even if it is only the paint cracking, there is some type of deterioration going on, or the paint may have cracked due to an impact and the shell popped back out. The best advice is still to replace the helmet.
To sum up, cracks in a helmet are never good, and usually indicate a loss of performance or the onset of some type of deterioration. The best advice is always to replace the helmet now.
This page was updated or partially revised on: October 27, 2016.