Isn't bamboo naturally antibacterial?
That claim is everywhere, so we read what the research actually says.
- Bamboo contains substances that can inhibit bacteria. In the skin of young moso bamboo shoots, researchers have found 2,6-dimethoxy-p-benzoquinone, a compound that inhibits several kinds of bacteria in lab tests. Bamboo powder has also shown some effect in the lab, linked to substances in the lignin.
- But that doesn't mean a finished bamboo product protects itself. When researchers tested natural bamboo fibre against bacteria and yeast, they found no effect at all. What works in a test tube with an extract doesn't have to work in a toothbrush handle.
In short: don't count on the bamboo keeping mould away by itself. Care is what makes the difference.
Why can bamboo go mouldy?
About half of a bamboo culm is made of cells that store nutrients, including starch and sugar. For mould, that's food. Add moisture and warmth, as in a bathroom, and it has everything it needs.
That's why many manufacturers heat-treat the bamboo. Heating breaks down some of the starch and sugar and makes the bamboo more resistant to mould. A thin layer of oil or wax can also make the bamboo take up less water.
How the bamboo in our 4-packs is treated
The bamboo in our horsehair bamboo toothbrush 4-pack and in our bamboo brush heads for Sonicare (4-pack) is heat-treated. That removes some of the nutrients mould would otherwise live on.
The bamboo also has a thin layer of food-grade white mineral oil, also called paraffin oil. It's the same kind of oil found in baby oil and skin creams. The oil consists of saturated hydrocarbons that don't mix with water. It soaks into the bamboo and makes water bead on the surface instead of being drawn in, at least to some degree.
It's important to understand what the oil doesn't do: it is not an anti-mould agent. It only makes the bamboo take up less water. What matters most is still letting the brush dry between uses.
The oil doesn't form a hard film on the surface, so it isn't a plastic and can't wear off as microplastic. It doesn't go rancid either, the way cooking oils can.
How to recognise mould
- Small black, green or grey dots, sometimes fuzzy.
- Usually at the bottom of the handle, where it stands in the cup, or where the brush head meets the handle.
- This isn't mould: even dark areas in the wood. That's the bamboo's natural grain or the colour from heat treatment. They're part of the material and can't be rubbed off.
What do I do if my brush has gone mouldy?
- Mould on the bristles or the brush head: replace the brush. It's something you put in your mouth, and it can't be cleaned safely.
- A small spot on the handle: scrub it with a brush dipped in vinegar, rinse and let it dry standing up. Vinegar works on many common moulds, but not all. If the spot comes back, or sits deep in the material, replace the brush.
- Not sure? Replace it. A new brush costs less than taking the chance.
How to prevent mould
- Let the brush dry standing up after every use. Shake off the water first.
- Watch the cup. Water easily collects at the bottom, and then the end of the handle stands in water around the clock. Empty the cup and let it dry now and then.
- No closed cases while the brush is wet. Let it dry first, or choose a case with air holes.
- Keep it somewhere airy, not in a cabinet without ventilation. One study found the most bacteria on brushes kept in bathrooms with a toilet, so close the lid when you flush and keep some distance from the toilet.
- Replace it about every three months, or sooner if the bristles splay.
What do studies say about bamboo versus plastic?
There are only a handful of small studies, and they point in different directions:
- One study found fungi, mainly the yeast Candida, on more bamboo brush heads than plastic ones. The researchers thought the organic material may favour fungi.
- Another study found the opposite: less microbial contamination on bamboo brushes than on regular plastic ones.
- In several studies, storage mattered more than material. Damp bathrooms and standing water gave the most growth.
The conclusion is the same whatever the material: a brush that gets to dry properly is a fresher brush.
Frequently asked questions
Can I oil the handle to protect it?
The bamboo in our horsehair toothbrush 4-pack and our brush heads already has a thin layer of mineral oil from the factory. If you want to top it up after a few months, rub in a drop of paraffin oil or baby oil and wipe off the excess. Avoid ordinary cooking oil, as it can go rancid. According to research, oil only gives limited protection against mould, so drying is still what matters most.
Does vinegar help against mould?
Vinegar can remove surface mould on the handle. For smells in the bristles, see our guide Does your toothbrush smell? If mould has got into the bristles, replace the brush.
Is a mouldy brush dangerous?
Mould doesn't belong in your mouth, which is why the brush should be replaced. If you have questions about your health, talk to a dentist or your doctor.