When Should You Replace a Cot Mattress?
This article offers general information and isn't a substitute for professional advice. Always follow current NHS and Lullaby Trust safer-sleep guidance, and speak to your health visitor or GP with any questions or concerns about your baby's sleep.
A cot mattress doesn't come with an obvious expiry date, which leaves a lot of parents quietly unsure whether the one they have is still fine or quietly past its best. It matters more than with an adult mattress, too, because a baby's sleep surface is tied directly to safe-sleep guidance. So if you're wondering whether yours needs replacing, here's how to judge it, and why the answer leans towards caution.
The short version: a cot mattress should always be firm, flat, clean and a proper fit, and the moment it stops being any of those, it's time to replace it.
Why a Cot Mattress Is Different
With an adult mattress, the worst consequence of leaving it too long is a poor night's sleep. With a cot mattress, the stakes are higher, because safe-sleep guidance depends on the surface itself. Safer-sleep advice is clear that a baby should sleep on a firm, flat mattress with a fitted sheet and nothing else in the cot, since a sagging, soft or poorly fitting mattress is linked to a raised risk during sleep.
That's why a cot mattress isn't something to stretch out for sentimental reasons or to save money. A surface that has softened, dipped or developed gaps around the edges has stopped doing the one job that matters most, and at that point its age is beside the point: it needs replacing regardless of how new it looks.
Signs It's Time to Replace Your Cot Mattress
There are clear physical signs to watch for. If the mattress has visible sagging, dips or permanent indentations where your baby lies, it has lost the firm, even support it's meant to provide. Lumps, exposed springs, or a surface that no longer springs back when pressed are all signals it's done. Any tears, holes or damage to the cover are also a reason to replace, since they let moisture and bacteria into the core.
Hygiene is the other half of it. Cot mattresses absorb a great deal of moisture, and persistent stains, smells or signs of mould that won't clean away mean the core has been compromised. A mattress that no longer fits the cot snugly, leaving gaps wider than roughly two fingers between the mattress and the cot sides, is also unsafe and should be changed, whatever its condition otherwise.
What About Second-Hand Mattresses
Reusing a cot mattress, whether between siblings or from someone else, is an area where safer-sleep guidance urges particular care. Some research has suggested a possible link between used cot mattresses and raised sleep risk, so the cautious advice is that if you do reuse one, it should have been cared for properly, with a completely waterproof cover and no signs of damage, and stored clean and dry.
Many parents simply choose a new mattress for each baby for peace of mind, which removes the uncertainty entirely. If you're reusing one, check it rigorously against all the firmness, fit and hygiene points above, and if there's any doubt at all, replace it. With infant sleep, the safe choice and the right choice are usually the same one.
How Long Do They Last?
There's no single fixed lifespan, because it depends on use, quality and how well the mattress has been protected. As a rough guide, many cot mattresses are designed to last only a few years of regular use before the firmness and hygiene start to decline, and heavy use shortens that. The condition checks above matter far more than the calendar, so inspect it regularly rather than relying on age alone.
A waterproof, wipeable cover or a separate protector extends a cot mattress's usable life considerably by keeping moisture out of the core, which is the thing that most often finishes them off. Even so, once any of the firmness, fit or hygiene signs appear, those override the clock entirely.
Looking Ahead to the Next Bed
A cot mattress only serves for the first stage. When your child outgrows the cot and is ready to move into their first proper bed, usually somewhere around two to three years old, they'll need a new, appropriately sized children's mattress designed for that stage rather than a hand-me-down adult one.
For that transition, a supportive kids' mattress for their first bed is built for a child's weight and a children's bed frame, giving proper support as they grow. The cot mattress and the first-bed mattress are two separate purchases for two separate stages, so plan to replace rather than repurpose when the time comes.
Protecting the Mattress You Have
Whether your cot mattress is new or you're trying to get more (safe) life out of it, protecting it properly is the single best way to keep it in good condition for longer. A waterproof, breathable mattress protector - like the lining that comes built into our Simba cot mattress - forms a barrier against the leaks, dribbles and spills that are an inevitable part of cot life, stopping moisture from soaking into the core where it causes the staining, smells and mould that eventually finish a mattress off.
FAQs
There's no fixed date, but many last only a few years of regular use before firmness and hygiene decline. The condition matters more than age: replace it as soon as it sags, loses firmness, no longer fits snugly, or shows damage or staining that won't clean away.
Visible sagging, dips or permanent indentations, lumps or a surface that won't spring back, tears or holes in the cover, persistent stains, smells or mould, and any gap wider than about two fingers between the mattress and cot sides.
Safer-sleep guidance urges caution, as some research suggests a possible link between used cot mattresses and raised sleep risk. If you reuse one, it should have a fully waterproof cover, no damage, and have been stored clean and dry. If in doubt, replace it.
Yes. Safer-sleep advice is for a firm, flat mattress with a fitted sheet and nothing else in the cot. A soft, sagging or dipped mattress has lost the firm support that safer-sleep guidance depends on, so it should be replaced regardless of its age or how new it appears.
Usually around two to three years old, when they outgrow the cot and move to a first bed. At that point they need a new children's mattress sized for that stage, not the old cot mattress or a hand-me-down adult one.
This article offers general information and isn't a substitute for professional advice. Always follow current NHS and Lullaby Trust safer-sleep guidance, and speak to your health visitor or GP with any questions or concerns about your baby's sleep.
