At present, our Highway Code does not provide for an “expiry date”, also because a lot depends on how it is used and the care devoted to it during its maintenance.
However, it must be considered that the materials any helmet is made of are subject to normal wear and tear and thus to a gradual decay of the intrinsic mechanical characteristics of the material itself.
To be even clearer, the condition of the materials used (such as HRT and HPC) to manufacture a helmet that has just been placed on the market will be better than that of a helmet that has been worn for more than 4 years, in summer and winter!
Although this may sound like an obvious and sensible consideration, it is always worth striving for the utmost clarity when expressing concepts that are debatable, as there is no law that regulates them.
A golden rule in this sense is that of carefully analysing the whole helmet in order to check its condition. Deep scratches on the decals, the paint or the visor, streaks that do not disappear with mild soap, unglued air vents or damaged clips, frayed and worn straps, unstitched interiors; these are all signs that a helmet needs maintenance or even to be replaced!