Do bike helmets expire if you never crash them?

They degrade slowly rather than expiring on a date. UV embrittles the shell, and heat and sweat affect the foam and the straps. Most manufacturers suggest replacement around five years, which is conservative but not arbitrary.

Why it happens

The dominant factor is ultraviolet exposure, which makes polycarbonate progressively more brittle. A helmet stored indoors ages far more slowly than one left on a bike or in a car rear window — where the temperature alone is also a problem.

Sweat is the second factor. It is mildly acidic and it soaks into the comfort padding and the webbing, and over years it degrades both the straps and the foam surface they attach to. Retention is what puts the helmet in the right place at the moment of impact, so this matters more than it sounds.

Five years is a manufacturer's estimate rather than a measured failure point. A lightly used helmet stored indoors will likely still perform; one that has lived outdoors for three summers may not.

What to do about it

1. 1Store it indoors and out of direct sunlight — this extends usable life more than anything else.
2. 2Inspect the straps and cradle rather than the shell. Frayed webbing and a ratchet that no longer holds are the practical signs.
3. 3Replace comfort padding when it degrades. It contributes nothing to impact protection but it sets the fit, and fit is what makes the rest work.