A second-hand helmet is the one piece of motorcycle equipment where you cannot inspect the thing you are actually buying. The protective structure is a crushable foam liner hidden under a shell and a fabric lining, it is destroyed by a single impact, and the damage is frequently invisible. Add a seller with an obvious financial reason not to mention the time they dropped it off the pillion seat at 90 km/h, and the calculation is straightforward. Buy the cheapest new certified helmet that fits you properly rather than the expensive used one, because a correctly fitting entry-level helmet outperforms a flagship helmet with a compromised liner every time.
The liner is a one-use structure and you cannot see it
Everything else follows from this. The Snell Memorial Foundation describes the mechanism plainly in its FAQ: motorcycle helmets are crash helmets that manage severe impact shock in one accident only, the crushable liner absorbs that shock by collapsing itself, and a helmet damaged that way cannot protect the brain a second time.
The problem for a buyer is detection. Snell states that without a thorough inspection by a trained professional it can be difficult to determine whether a helmet has been damaged and its protective capability compromised. If a foundation that runs an accredited helmet test lab says that, a rider holding the helmet in a car park has no chance.
The regulator makes the same point from another direction. 49 CFR 571.218 requires every helmet to carry a label warning that a helmet "can be seriously damaged by some common substances without damage being visible to the user", along with the instruction that a helmet which has experienced a severe blow should be returned to the manufacturer for inspection, or destroyed and replaced.
Note what that clause implies about used sales. The correct disposal of a struck helmet is destruction. A struck helmet reaching a classified ad means someone chose not to follow that.
Six things you cannot verify about a stranger's helmet
Whether it has been in a crash. The seller's word is the only evidence, and a rider selling a crashed helmet is not going to say so. Low-speed get-offs where the rider was unhurt are exactly the ones people talk themselves out of mentioning.
Whether the liner has been crushed. A liner can take a permanent set from a heavy object falling on it, from being hung on a mirror for two years, or from heat in a car boot, and none of that leaves an external mark.
Whether it has been exposed to solvents. Petrol splash at a fuel stop, insect remover, a cleaning product not on the manufacturer's approved list. FMVSS 218 warns about exactly this because the damage does not show.
How it has been stored. Summers on a rear parcel shelf, a garage next to a heater, a shed with a leaking roof. Heat softens EPS and UV embrittles thermoplastic shells.
Whether the certification is real. Snell publishes warnings about counterfeit certification labels sold openly through online marketplaces. Anyone can buy a sticker.
Whether the fit has gone. This one you can partly assess, and it is the most common problem with a used helmet. Snell notes that helmets with worn-out pads are effectively one to two sizes larger than they were when new, which is why a used helmet often feels comfortable immediately — and immediate comfort is the classic sign of a helmet that is too big.
Hygiene, which is the part people underestimate
A helmet liner absorbs sweat, skin oil, dead skin and hair products for years. Fungal scalp infections and folliculitis transfer readily through shared headgear, and a liner that has not been washed is a warm, damp, protein-rich environment.
Some of this is fixable: many modern helmets have fully removable, washable liners and cheek pads, and replacement pad sets are available as spare parts for most current models. If the model is recent enough that pads are still stocked, a full replacement liner set solves the hygiene problem outright — the method is in helmet cleaning and care. If the helmet is old enough that pads are discontinued, it is old enough that you should not be buying it anyway.
Where the risk actually sits
| Source | Crash history known | Age known | Certification verifiable | Verdict |
|---|---|---|---|---|
| New from an authorised dealer | Yes, none | Yes, on the label | Yes | The default |
| New old stock, discounted, sealed | Yes, none | Yes, check the date | Yes | Fine if the manufacture date is recent enough |
| Ex-display or shop demo helmet | Yes, none | Yes | Yes | Acceptable; liner may already be loosened by try-ons |
| Used, from a rider you know well | Only as well as you trust them | Yes, on the label | Yes | The only used case with a defensible argument |
| Used, from a classified ad or marketplace | No | Sometimes | Sometimes | Avoid |
| Used, from an auction or house clearance | No | No | No | Avoid |
| Track day or race helmet being sold on | Almost certainly used hard | Yes | Yes | Avoid |
If you are going to do it anyway
Some riders will buy used regardless, usually because the alternative is riding in something worse. If that is the situation, these checks reduce the risk without eliminating it.
1. Only from someone you can question properly. A friend, a club member, someone whose riding history you know. Not a stranger with a photo.
2. Find the manufacture date first. It is on a permanent label, required by FMVSS 218 in the US and marked on ECE helmets. Anything more than about two years old has already spent a meaningful part of the recommended service life, and the reasoning is in helmet replacement intervals. Walk away from anything over three years.
3. Verify the certification against the source, not the sticker. Snell publishes a certified helmet list by model and size, updated daily, at smf.org/cert. For a DOT label, check the format: model designation and brand above the DOT symbol, with "FMVSS No. 218" and "CERTIFIED" beneath, and nothing else on that label.
4. Strip the liner out and inspect the EPS. Press over the whole surface with your thumb looking for soft spots, texture changes, hairline cracks or areas pulled away from the shell. If the seller will not let you do this, that answers the question.
5. Run the full fit test. Rotation test, roll-off test, ten minutes on your head. Used helmets fail this far more often than new ones because the pads are compressed — see helmet sizing and head shape for the sequence.
6. Budget for a new liner set. Add the cost of replacement cheek pads and crown liner to the asking price before deciding whether it is a bargain. Frequently it stops being one.
7. Reject anything with drilled holes or glued mounts. A shell with a hole in it has been structurally compromised, and Snell states that installing aftermarket accessories can invalidate certification. If the previous owner wanted a camera or intercom badly enough to drill, assume the rest of the helmet was treated the same way. Non-invasive alternatives exist, including keeping navigation on a handlebar riding display so the helmet only carries audio through its own speaker pockets.
The honest summary is that all seven checks together still cannot tell you whether the liner has been crushed, which is the failure mode that matters most. They reduce the probability of buying something obviously bad. They do not make a used helmet equivalent to a new one.
Selling your own helmet.
The same logic applies in reverse, and it is worth being straight about. If your helmet has been in any impact with your head inside, do not sell it, give it away or leave it on a shelf where someone else might use it. Cut the strap and break the liner so it cannot be worn. That is what the FMVSS 218 label instruction means by "destroy it and replace it".
If it has never been struck and is under a year old, selling it is defensible — say exactly how old it is, quote the manufacture date from the label, and confirm it has not been dropped. The buyer still cannot verify any of that, which is the whole problem, but at least the information you supply is true. And if you are selling because you crashed, the article on helmets after a drop or crash covers what to do with the old one, including why you may want to keep it until any injury claim is settled.
Frequently asked questions
Can you tell if a used helmet has been crashed?
Not reliably. Snell states that without a thorough inspection by a trained professional it can be difficult to determine whether a helmet has been damaged and its protective capability compromised. Removing the liner and inspecting the EPS will catch obvious crush damage and nothing subtler.
Is it safe to buy a used helmet from a friend?
It is the only used case with a real argument, because you can ask about crash history and get an answer you can weigh. Check the manufacture date, strip the liner, run the fit tests, and budget for new pads. The residual risk is that your friend does not remember, or does not consider a slow tip-over worth mentioning.
What about an unworn used helmet still in its box?
The crash risk is low, so the question becomes age. Find the manufacture date on the internal label. Snell notes that unused helmets stored in good condition do not automatically expire at five years, but you have no idea whether "stored in good condition" describes a cool cupboard or a hot loft.
Can I just replace the liner in a used helmet?
You can replace the comfort padding and cheek pads, which fixes fit and hygiene. You cannot replace the EPS impact liner, which is bonded into the shell and is the part that would have been damaged in a crash. New pads solve the problems you can see.
Are ex-display helmets from a shop a reasonable buy?
Usually yes, since the crash history is known to be none and the certification and date are verifiable. The one caveat is that a helmet tried on by hundreds of people has partially compressed pads already, so check the fit carefully and expect it to loosen faster than a new one.
