Is a second-hand car seat safe?

The verdict

The answer is not never. It is only with a known history, and the difference between a seat from your sister and a seat from a car boot sale is the whole answer.

RoSPA's guidance is the clearest framing available: never buy these items second-hand unless you are assured of their history, because they are one hit products, something that must not be used again if involved in an incident. It explains why: involvement in an accident or simply dropping the item can affect the internal structure, even if any damage is not visible on the exterior. If it is not structurally sound, then it will not protect you or your child.

Then it draws the line that actually matters: if you are getting a second-hand car seat from a relative or friend that you know well, and know the full history of the product and that it has not been subject to damage, then that is very different from buying it at a car boot sale where the seller may not be as honest about its history. Our advice is to never buy one of these items if it has been involved in some kind of accident already.

Health Canada puts the same rule in one sentence: do not use a car seat or booster seat if the seller or lender does not know the history of the seat.

Why a car seat is different from a pushchair

A car seat works once, and it works by deforming. Energy-absorbing foam crushes, the shell flexes, webbing stretches. Those are single-use behaviours. A seat that has already absorbed an impact has spent the capacity it was going to protect your child with, and a great deal of that damage is internal and invisible.

RoSPA's own summary is that when you buy a second-hand car seat, crash helmet, cycling helmet or riding helmet, in most cases, you cannot know for sure if it has been damaged, but that vital information could make the difference between life and death.

It is worth remembering what the seat is buying you. RoSPA cites a Swedish study finding that rearward facing child seats reduced the likelihood of injury by 90% compared with being unrestrained, and that forward facing seats which help position the seat belt correctly reduced the risk of injury by 77% for four to ten year old children. A compromised seat is a compromised version of that.

The checklist

NHTSA publishes the most usable version. If you can check off each one of these statements, then the second-hand seat may be okay to use:

• The seat has never been involved in a moderate to severe crash.
• The seat has labels stating date of manufacture and model number. You need this information to find out if there is a recall on the car seat or if the seat is too old.
• The seat has no recalls. If you do find a recall, contact the manufacturer, as some problems can be fixed.
• The seat has all its parts. If a part is missing, contact the manufacturer, as some parts can be ordered.
• The seat has its instruction book. You can also order the instruction manual from the manufacturer.

Health Canada adds a Canada-specific requirement and some mechanical checks. Make sure the seat has a National Safety Mark, which is proof that the seat meets the Canadian safety standards; comes with a manual, with all parts listed in the manual included and in good working order; and has not been in a vehicle during a collision. When shopping, check that it has a buckle that you can latch and unlatch, a harness that you can tighten and loosen, a chest clip that closes easily and remains closed, and an anchoring system in good working order.

Health Canada also tells parents to check both Transport Canada's safety alerts and notices for child car seats and Health Canada's recalls and safety alert database before buying or borrowing.

The missing-instructions problem

RoSPA makes a general point about second-hand goods that applies with force here: one of the biggest problems with these second-hand items is a lack of instructions, because often re-sold items no longer contain the warnings and instructions that came with them when new. A car seat fitted wrongly is a substantial part of the risk, and the manual is how you fit it right. Manufacturers will supply a replacement.

Expiry dates, which exist in some countries and not others

This is the part most people get wrong, because the answer depends on where you live.

In the UK there are no expiry dates. RoSPA states it flatly: in the UK, car seats are not marked with an expiry date. It adds that many manufacturers recommend that you replace or upgrade your child car seats after five years, because child car seats are constantly being improved and upgraded, but that some seats on the market are now suitable for children from birth up to 36kg, about 79 lb, and are therefore designed to last for a longer period of time.

In Canada they are near-universal but not compulsory. Transport Canada states that although not required by regulation, most, if not all, child car seats and booster seats sold in Canada have an expiry date or useful life date on them, found on a label affixed to the seat or in the instruction manual. Health Canada repeats that expiry dates are indicated on most car seats and booster seats even though it is not required by law.

In the US, dates of manufacture are required on the label, and NHTSA's checklist treats those labels as the means of finding out whether a seat is too old or subject to a recall.

Transport Canada adds a legal warning with real teeth for hand-me-downs: if a seat was made before 1 January 2012, it may be illegal to advertise, sell, or give it away, because it may not meet the latest safety standards.

After any collision

Replace it. RoSPA's advice is that it is recommended that you replace the seat if it is involved in a collision, and Health Canada's second-hand rule excludes any seat that has been in a vehicle during a collision. Transport Canada advises that a seat past its expiry or useful life date should be permanently discarded rather than donated to a charitable organisation, second hand store, or given to friends or relatives.

Destroying an expired or crashed seat rather than passing it on is the part people skip, and it is how unsafe seats re-enter circulation.

Where guidance genuinely differs

Expiry dates: universal in Canada, absent in the UK. Transport Canada records that most, if not all, seats sold in Canada carry an expiry or useful life date, though this is not required by regulation. RoSPA states that in the UK car seats are not marked with an expiry date at all, and offers a manufacturer rule of thumb of five years instead. A Canadian parent checks a printed date; a British parent has no date to check.

Canada makes some second-hand seats unlawful to pass on. Transport Canada warns that a seat made before 1 January 2012 may be illegal to advertise, sell, or give away in Canada. There is no equivalent UK or US cut-off date for private transfer.

Canada requires a certification mark on the seat itself. The National Safety Mark is Health Canada's proof that the seat meets Canadian standards, and its absence rules a seat out. UK and EU seats carry E-mark approval labels instead, and US seats carry a federal compliance label.

Everyone agrees on the core. No crash history, all parts, labels, manual, no open recall. If any one of those is missing, the honest answer is no.