Does your toothbrush smell? How to freshen up natural bristles

Why can natural bristles smell?

Natural bristles, such as boar bristle and horsehair, are made of keratin. That's the same protein as in our own hair, and just like hair it soaks up water. If the brush stays wet for a long time, for example in a closed case or at the bottom of a cup, bacteria thrive in the damp. That's when it can start to smell sour or musty.

So the most important thing is to let the brush dry properly between uses.

What you need

• Two glasses, for example drinking glasses or egg cups
• Vinegar. Regular white vinegar works as it is. If you use strong 12% vinegar, mix it with the same amount of water.
• Baking soda, one tablespoon stirred into a glass of lukewarm water

Step by step

1. Rinse the brush well under running water.
2. The vinegar bath: dip the brush head in the vinegar and swirl it around for about a minute.
3. Rinse well with water.
4. The baking soda bath: dip and swirl in the baking soda solution for about a minute. This also removes the vinegar smell.
5. Rinse well one last time.
6. Let it dry standing up where the air can reach it, ideally for a few hours before you use it again.

Why does it work?

Vinegar contains acetic acid, a weak acid. It deals with odour compounds that are basic and makes the surface too acidic for many of the bacteria behind the smell. Baking soda is a weak base. It deals with odour compounds that are acidic, and with the last traces of vinegar.

That's why you rinse between the steps. If you pour vinegar and baking soda into the same glass, they react with each other. It fizzes nicely, but what's left is mostly water, carbon dioxide and sodium acetate, so you've used both up before they could do any good.

What to avoid

• Don't boil the brush. High heat can damage the bristles and crack the bamboo.
• Don't leave it soaking. Bamboo swells in water. Short dips are enough.
• Don't use chlorine or bleach. They're far stronger than needed and shouldn't be left on something you put in your mouth.
• Not in the dishwasher or the microwave.

How to keep it from smelling

• Shake off the water and let the brush dry standing up after every use.
• Don't put it in a closed case while it's wet. Let it dry first, or use a case with air holes.
• If several brushes share a cup, make sure they aren't squeezed together so the bristles never dry.
• Replace the brush about every three months, or sooner if the bristles splay. Read more in How often should you replace your toothbrush?

When is it time to replace it instead?

If the smell comes back within a couple of days, or you see discolouration or mould, replace the brush. That goes for every toothbrush, whatever it's made of. A worn-out bamboo brush doesn't have to end up as rubbish. See How to compost your bamboo toothbrush.

Frequently asked questions

Can I mix vinegar and baking soda to save time?

No. They cancel each other out and turn mostly into water and carbon dioxide. Use them in two separate glasses and rinse in between.

Does it work on electric toothbrush heads?

Yes. Take the head off the handle and do the same thing, but only dip the head.

How often can I do this?

Whenever it's needed. For most people, letting the brush dry properly is enough, and then it's rarely or never needed.