To get the smell out of a swim cap, wash the inside with lukewarm water and a drop of mild soap, soak the cap for 15 to 30 minutes in cool water with a spoonful of bicarbonate of soda, rinse it thoroughly, and let it dry completely before it goes back in your bag. Most swim cap smells come from damp residue sitting on the silicone, not from the silicone itself, so they wash out.
If the smell is back within a week, the cap is not the real problem. The drying routine or the kit bag is, and both are easy to fix. This guide is for a cap that already smells. For the everyday rinse-and-store routine that stops it happening, see how to clean and store a silicone swim cap.
Why swim caps start to smell
Silicone is smooth and does not soak up water the way fabric does. What smells is the film that builds up on it: sweat and skin oils from your forehead, conditioner or hair oil, sunscreen and pool water. Pack that film into a closed bag while it is still damp and warm, and it turns musty in exactly the way a forgotten towel does.
The sharp “swimming pool” smell has a different source. It comes mostly from chloramines, compounds that form when chlorine reacts with sweat and everything else swimmers bring into the water. They cling to skin, hair and kit, which is why a cap can smell of the pool hall hours after you left it.
Then there is the bag. A swim bag that never dries out properly smells on its own, and anything packed into it picks that up. Washing the cap and putting it back in the same bag is like showering and pulling yesterday's socks back on.
Match the smell to its cause
Sniff the inside of the cap first, then the outside. The type of smell tells you what needs fixing.
| What it smells like | Likely cause | Fix |
|---|---|---|
| Musty, like a damp towel | Packed away wet, or a bag that never dries | Reset wash, a full dry, and air the bag too |
| Sharp and chemical, like the pool hall | Chloramines left on the surface | A long fresh-water rinse, then a mild soap wash |
| Sour or sweaty | Sweat and skin oils on the inside band | Soap wash, concentrating on the band along your hairline |
| Perfumed, waxy or oily | Conditioner, leave-in products or sunscreen | Soap wash, twice if needed, with a longer rinse |
| Weedy, earthy or fishy | Lake or sea water, silt and algae | Rinse the inside as soon as you can, then a reset wash |
| Faintly rubbery on a new cap | A fresh-out-of-the-packet smell | Rinse it and let it air in the shade; it usually fades within days |
| Musty after two reset washes, with a tacky surface | The surface has started to break down | Retire the cap |
The reset wash, step by step
- Rinse both sides under cool running water. Turn the cap inside out so the water reaches the band that sits on your forehead.
- Wash the inside with a drop of mild soap. Hand soap, gentle shampoo or washing-up liquid all work. Use your fingertips, not your nails, and spend most of the time on the inside, because that is where the smell lives.
- Soak it with bicarbonate of soda. Dissolve a spoonful of bicarbonate of soda (baking soda) in a basin of cool water and submerge the cap for 15 to 30 minutes. A cap traps air and bobs up, so weigh it down with a mug.
- Rinse thoroughly. Keep going until the surface no longer feels slippery. Soap left behind can itch on a sensitive scalp.
- Dry it completely. Lay it flat with the edge propped open, turn it over once, and leave it out overnight. A cap that is dry outside but damp inside will smell again by your next session.
- Do the sniff test the next day. Inside first. If it still smells, repeat the wash and soak once more.
What not to use on a smelly cap
- Bleach or disinfectant sprays. A cap needs cleaning, not sterilising, and harsh chemicals are hard on printed designs and on your scalp if any residue stays behind.
- Neat vinegar. It swaps one smell for another. Bicarbonate of soda does the job without the salad-dressing finish.
- Boiling water. Fine for a silicone baking mould, not worth the risk for a thin printed cap.
- The washing machine or dishwasher. Hand washing is gentler, and a basin is quicker anyway.
- Perfume, fabric spray or a dryer sheet stuffed inside. They hide the smell for a day and leave residue that ends up on your head.
- A sunny windowsill to “air it out”. Shade and moving air dry it just as well, without fading the print.
Check the kit bag, not just the cap
If a freshly washed cap starts smelling again within a few sessions, look at what it travels in. A closed gym bag holding a wet towel, a damp costume and a cap is a very efficient smell factory.
- Empty the bag on the day you swim and leave it open to dry.
- Carry wet kit in a separate mesh or wet bag, and keep the cap out of the towel roll.
- Wash the bag itself now and then, following its label.
- Don't leave the bag in a warm car boot overnight.
- For kids, check the school swim bag on Friday afternoon, not Monday morning.
How to stop the smell coming back
Prevention takes seconds; the reset wash takes half an hour. Rinse the inside after every swim, even a short one, unpack as soon as you get home, and only store the cap once it is dry inside.
If you swim on back-to-back days, one cap often does not get time to dry properly between sessions. Rotating two caps fixes that: one on your head, one drying at home. The CutWave Duo Pack lets you pick any two designs for €27.99, which also clears the free EU shipping threshold.
Swimmers with long, curly or braided hair who use leave-in products will find the inside builds up faster, so a soap wash after those sessions beats a quick rinse. The pre-swim leave-in routine in our guide to protecting braids, curls and textured hair under a cap is still worth keeping; just wash the cap after it. And if it is your hair that smells of the pool rather than the cap, that is a separate problem, covered in our guide on whether swim caps protect hair from chlorine.
When the smell means the cap is finished
A musty smell that survives two reset washes and a full dry, especially with a tacky, chalky or flaky surface, means the surface itself has started to break down. More washing will not bring it back. At that point it is a replacement question rather than a cleaning one, and our guide on how often to replace a swim cap walks through the other signs to check.
FAQ
Is it safe to swim in a swim cap that smells?
A musty smell usually means residue and damp rather than anything dangerous, but it is not pleasant against your scalp. Give the cap the reset wash before your next swim. If your scalp itches or develops a rash, stop wearing the cap and speak to a pharmacist or doctor.
Will bicarbonate of soda damage the print on my cap?
As a short soak, dissolved in plenty of cool water and rinsed off afterwards, it is gentle. Avoid scrubbing the print with a thick paste, because bicarbonate of soda is mildly abrasive.
How do I get the smell out of a latex or fabric swim cap?
Latex takes the same gentle soap wash and full dry, and many swimmers dust it lightly with cornflour afterwards so it does not stick to itself. Fabric caps are usually washed like swimwear. In both cases, check the label first.
Should I clean my goggles the same way?
Rinse goggles in cool fresh water and let them air-dry, but do not rub or soak the inside of the lenses, because that can wear away the anti-fog coating. Keep them out of the bicarbonate soak.