Insoles smell because bacteria living on your skin transfer into the foam along with perspiration, and then feed on it. The odour is a by-product of that process, not the sweat itself. Foam holds moisture well, which is exactly what makes it comfortable and also what makes it smell.
The short version: dry the insole out completely, then treat it with bicarbonate of soda overnight. That clears most cases. Washing works too, but only on insoles designed for it, and drying afterwards matters more than the wash.
Where the Smell Actually Comes From
Sweat is close to odourless when it leaves your skin. The smell develops when bacteria break it down, and that process needs moisture, warmth and time. A shoe worn daily provides all three.
Insoles hold odour more strongly than the rest of the shoe for a simple reason. They are the layer in direct contact with your foot, they are usually made of open-cell foam that absorbs readily, and they rarely get the chance to dry fully between wears.
This is why an insole can smell noticeably worse than the shoe it came out of, and why masking the smell without removing the moisture never works for long. Deodorising sprays treat the symptom. The bacteria and the damp are still there an hour later.The short version: dry the insole out completely, then treat it with bicarbonate of soda overnight. That clears most cases. Washing works too, but only on insoles designed for it, and drying afterwards matters more than the wash.
Check Whether Your Insole Can Be Washed
Do this before you get anything wet, because the wrong method ruins some insoles permanently.
- Usually washable by hand: plain foam insoles, fabric-topped foam, and most basic replacement insoles.
- Surface clean only: insoles with a rigid plastic or TPU shell, gel-filled sections, layered or laminated construction, leather or suede tops, and anything with printed graphics. Water gets between layers in laminated insoles, and the adhesive fails.
- Follow the manufacturer’s instructions: heat-mouldable insoles and custom orthotics. Custom orthotics in particular should be cleaned as prescribed rather than experimented with.
- Never machine wash any of them. Agitation and spin cycles break down foam structure, and the heat in most machine cycles weakens adhesive between layers. An insole that survives one machine wash usually does not survive three.
If you are unsure which category yours falls into, treat it as surface clean only. That method works on everything and damages nothing.
Four Ways to Clear the Smell
Start with the first and stop when the smell has gone. Most cases resolve at method one or two.
Method 1: Dry it out completely
Removing the moisture removes what the bacteria live on, and a surprising number of odour problems are solved by this alone.
Take the insoles out of the shoes and stand them on edge or lay them flat somewhere warm with moving air. Twenty-four to forty-eight hours is realistic for foam that has been damp for weeks. A fan speeds it up considerably.
Avoid radiators, hairdryers and direct sun. Heat sets foam in shape, weakens laminate adhesive, and can leave the insole curled at the edges.
Airing outdoors on a dry day works well, though not in strong sunlight.
Method 2: Bicarbonate of soda
Bicarbonate of soda absorbs moisture and neutralises the acidic compounds that produce the smell. It is the standard fix, and it costs almost nothing.
Sprinkle it generously over the top surface of a dry insole, leave it overnight or for a full day, then shake and brush it off thoroughly. Repeat if the smell has faded but not gone.
Brush it out properly. Bicarbonate left in the foam clumps as soon as it takes up moisture and can feel gritty underfoot.
Method 3: Surface wash
Safe for every insole type, including ones that should not be soaked.
Mix a little mild soap into warm water, dampen a cloth, wring it out well, and wipe the top surface. Follow with a cloth dampened in clean water to lift the soap, then blot with a dry towel and air-dry fully before the insole goes back in the shoe.
The insole should be damp at no point, not wet. If water is running off it, the cloth is too saturated.
Method 4: Full hand wash
Only for insoles you have confirmed are washable.
Use lukewarm water and a small amount of mild detergent. Work the surface gently with a soft brush, rinse thoroughly so no detergent remains in the foam, then press between towels to remove as much water as possible. Do not wring or twist, since that creases the foam permanently.
Air-dry flat for at least twenty-four hours, and often longer. An insole that goes back in the shoe still damp will smell worse within days than it did before the wash, because you have added moisture to the exact environment the bacteria need.
How to Stop It Coming Back
Clearing the smell is straightforward. Keeping it clear is about breaking the moisture cycle.
- Rotate your shoes. A pair worn every day never dries fully. Alternating between two pairs gives each a full day to dry and does more for odour than any product.
- Take the insoles out overnight. Even occasionally. An insole left inside a shoe dries from one side only and takes far longer.
- Change socks daily, and reconsider the material. Cotton holds moisture against the foot. Wool and technical synthetics move it away, which means less of it reaches the insole.
- Treat the shoe as well as the insole. Bacteria live in both. Cleaning only the insole and returning it to an untreated shoe reintroduces the problem.
- Dry properly after wet conditions. Shoes soaked by rain or washing need the insoles removed and both dried separately, not left as a unit.
When an Insole Cannot Be Rescued
Sometimes the smell has gone too deep, and it is worth recognising that rather than repeating treatments.
If odour returns within a day or two of a thorough dry and a bicarbonate treatment, bacteria are established through the full thickness of the foam rather than on the surface. Surface treatments will not reach them.
Deteriorating foam also holds odour more stubbornly. As open-cell foam breaks down with use, the structure becomes more porous and absorbs more readily. An insole that has compressed unevenly or lost its shape is usually near the end of its life anyway, and persistent smell is a reasonable prompt to replace it.
Most foam insoles have a useful life measured in months of daily wear rather than years. If yours has been in constant use for a year or more and now smells within days of cleaning, replacement is the honest answer.
Frequently Asked Questions (FAQs)
Q1. Can I put insoles in the washing machine?
No. Machine agitation breaks down foam structure, and the heat weakens the adhesive between layers in laminated insoles. Hand washing in lukewarm water is safe for insoles that are washable, and a surface wipe is safe for all of them.
Q2. Why do my insoles smell worse than my shoes?
The insole is the layer in direct contact with your foot; it is usually open-cell foam that absorbs readily, and it rarely dries fully between wears. Those three things together make it the part of the shoe that holds odour most.
Q3. Does freezing insoles kill the bacteria?
Not reliably. Freezing makes many odour-causing bacteria dormant rather than killing them, and they become active again as the insole warms. Any improvement is usually from the drying that happens in a freezer rather than from the cold itself.
Q4. Will antibacterial spray fix it permanently?
Only in combination with drying. Spray treats bacteria on the surface but does not remove the moisture deeper in the foam that allows them to return. Used alongside proper drying and rotation, it helps. Used on its own, it masks the smell for a few hours.
Q5. How often should insoles be cleaned?
For daily wear, a surface wipe every couple of weeks and a bicarbonate treatment monthly keeps most insoles fresh. Heavy activity or hot weather warrants more frequent attention. Drying insoles overnight regularly does more than any cleaning schedule.
