When do helmets have to be changed? Do they have an expiration date?
There are questions that seem absurd, but they make all the sense in the world. We take it for granted that a bicycle helmet does not expire but nothing could be further from the truth: a bicycle helmet has a usage time and some variables that determine its duration. We will explain this to you.
Why a bicycle helmet expires
The idea is simple: a bicycle helmet is made almost entirely of plastic materials, and this often transmits the feeling of eternity. But none of that, the materials derived from oil also degrade and lose properties, and that's why a bicycle helmet also expires.
Basically, the parts of a cycling helmet are made of the following materials: the so-called cork is expanded polystyrene, a kind of ball that under pressure and hydration swells and compacts, forming a rigid structure that is very absorbent to any impact. Well, starting with this one, let's say that sweat and water affect it notably. Polystyrene can last with full properties for about 5 years.
Of course, it depends on the use and care we give to the bicycle helmet. It is not the same a person who uses it once a week and another one who uses it every day. But the average is that: about 5 years according to the main manufacturers.
But there is more. The outer plate is made of moulded polycarbonate. It is the hardest and most resistant material in the helmet, but the high temperatures and constant use (scratches, scuffing) also cause it to degrade, even to become detached from its attachment to the cork. Therefore, the case becomes less safe as well. The main reason for this degradation is the incidence of sunlight, so protecting the helmet when not in use from sunlight will extend its life. It is not only a matter of aesthetics, that it loses colour or the paint peels off, as you can see.
But there is even more. The straps are made of nylon and the adjustment and fastening parts are made of very rigid plastic materials. They also have their degradation, in fact the straps constantly connect with one of the areas of most sweating: the area of the ears. Sweat, with its salts and acids, is slightly corrosive over time.
The main reason why a helmet expires
But the main reason a helmet expires and must be changed periodically is because of impact. When you hear that word, you might think of a brutal fall, but no, you should also consider the small impacts that the helmet receives over the years: falls to the ground from different heights, hits with other accessories, during transport, some stone or projectile or yes, a more or less important fall.
The manufacturers are clear: in the event of a fall or impact, the safest thing to do is to replace the helmet. You may think that is logical, because they may be trying to sell. But don't be so suspicious, because impact laboratory studies by companies and external laboratories corroborate this: helmets, in the impact machine, do not receive a single impact. In fact, approvals require at least two, at two different points. If a helmet cannot withstand the second impact, it cannot be approved.
Now, imagine a cracked helmet that receives a second impact in a hard fall. It will not protect as expected, and this can expose you to significant damage. You should not skimp on what is perhaps the only element of a cyclist's safety, on an element that saves thousands of lives every year. Pay no attention to manufacturers if you are suspicious, do not change your helmet every 2 or 3 years. But listen to science, and don't go with a decades-old helmet, especially one that's cracked or has fallen off. If you consider it, you may realize that the price of helmets today is not worth the risk.