There's a question most of us have never thought to ask.
We buy toothbrushes. We use them twice a day. We throw them away. We buy another one.
The packaging says "soft bristles" or "ultra-clean" or "dentist recommended." But it almost never tells you what those bristles are actually made of. And when you find out, you'll understand exactly why.
This is the part of the oral care industry that nobody advertises.
The Short Answer: Petroleum-Derived Plastic
The bristles on the overwhelming majority of toothbrushes sold today — regardless of price point, regardless of brand, regardless of whether the handle is plastic or bamboo — are made from nylon.
Nylon is a synthetic polymer. It is made from petroleum, the same fossil fuel used to produce gasoline, plastic bottles, and synthetic fabrics. There are two main variants used in toothbrush bristles:
- Nylon-6,6 — the most common, used in standard toothbrushes worldwide
- Polybutylene terephthalate (PBT) — a slightly firmer variant, often used in mid-range and premium brushes
Both are petroleum derivatives. Both are non-biodegradable. Both shed microplastic particles during use. And both have been inside your mouth, twice a day, for your entire life.
A Brief History of How Toothbrush Bristles Became Plastic
It wasn't always this way.
For most of human history, toothbrushes were made from natural materials. The handles were bone, wood, or bamboo. The bristles were animal hair — most commonly boar bristle or horsehair — materials that had been used in cleaning tools for centuries because they worked.
Then in 1938, DuPont introduced nylon to the world. And the toothbrush industry changed almost overnight.
Nylon was cheaper to produce at scale. It was consistent in a way natural bristles weren't — every bristle the same diameter, the same length, the same stiffness. It didn't require animal sourcing. And in the post-war manufacturing boom, "synthetic" meant modern, progressive, scientific.
The switch from natural to synthetic bristles wasn't driven by evidence that nylon was better for your teeth or gums. It was driven by economics and the cultural moment. Plastic was the future. Natural materials were the past.
Nearly 90 years later, most of us are still using the same basic material in our mouths every morning — we've just stopped thinking about it.
So What Exactly Happens When Nylon Meets Your Mouth?
Your mouth is a surprisingly aggressive environment for materials. It's warm, it's wet, it fluctuates in pH depending on what you eat and drink, and twice a day you're applying mechanical force — however gently you think you brush — across every surface inside it.
Under these conditions, nylon bristles do something that shouldn't be surprising once you think about it: they break down.
Not dramatically. Not visibly, for the most part. But at a microscopic level, the mechanical friction of brushing causes the nylon to shed tiny fragments — particles measured in micrometres, invisible to the naked eye. These are microplastics.
A 2024 study published in the Microchemical Journal simulated realistic brushing conditions and found that standard toothbrushes release an average of 39 microplastic particles per day. Other research has put the number between 30 and 120 particles per session.
These particles don't politely leave your mouth. They mix into your saliva. They get swallowed. They make contact with the highly permeable mucous membranes in your gums. And your body, which has no evolutionary mechanism for processing synthetic polymer fragments, has to deal with them as best it can. (For the wider context of how this fits into daily exposure, see our breakdown of bathroom chemical exposure.)
What About "Charcoal" Bristles?
You've probably seen them. Black bristles, heavily marketed as natural, detoxifying, or antibacterial. They look different. They feel different. So they must be different, right?
Not in any meaningful way.
Charcoal bristles are standard nylon bristles that have been infused with activated charcoal powder. The base material is still petroleum-derived nylon. The charcoal is a coating or additive — it changes the colour and adds some genuine antibacterial properties, but it does not change what the bristle is made of at a structural level.
Studies have confirmed that charcoal toothbrushes do show reduced bacterial contamination on the bristle surface — a real and legitimate benefit. But they still shed nylon microplastics during use, because the bristle itself is still nylon.
The charcoal is a feature. The nylon is still the bristle.
What About Plant-Based or Bioplastic Bristles?
This is where it gets genuinely complicated, and where a lot of well-meaning eco brands are currently operating in a grey area.
Some brands have moved away from standard petroleum nylon and toward "plant-based" bristles — typically made from bioplastics derived from castor oil or corn starch. The two most common are PA11 and PA10,10 — both nylon variants, but synthesised from plant oils rather than petroleum.
On paper, this sounds like a meaningful improvement. And in some ways, it is — the production process is less fossil-fuel-intensive, and the materials can biodegrade under certain industrial composting conditions.
But here's what the research says about whether they're safer in your mouth: we don't know yet.
As of now, there are no peer-reviewed studies confirming that plant-based bioplastic bristles do not shed microplastics. And a 2023 study published in the Journal of Hazardous Materials found that PLA bioplastics — one of the most widely used plant-based plastics — still shed microplastic particles under mechanical stress.
Bioplastics are plastics. They may be better for the planet in how they're produced. They may be better at end-of-life in the right composting conditions. But "plant-based" does not mean "doesn't shed microplastics." It just means the starting material was a plant rather than oil.
The One Bristle That's Genuinely Different
To find a bristle that sidesteps the microplastic question entirely, you have to go back before nylon. Back to what people were using for centuries before the plastics industry decided natural meant outdated.
Horsehair.
Horsehair bristles are made from actual horse hair — collected from mane and tail, a byproduct of the equine industry, processed with hot water only (no chemical treatments), and set into a bamboo handle. No polymers. No petroleum. No synthetic additives.
When a horsehair bristle wears down or breaks, it degrades into keratin — the same protein that makes up your own hair and nails. Not a synthetic polymer. Not a microplastic. Just an organic material returning to the environment.
This is a fundamentally different category of material from anything that comes out of a petroleum refinery or a bioplastics production facility — however green the branding around those facilities might be. (For the full head-to-head, see horsehair vs nylon: the honest comparison.)
Toothbrush Bristle Types Compared
Here's the honest picture of what's actually in the most common toothbrush bristle types:
| Bristle Type | Base Material | Petroleum-Derived? | Sheds Microplastics? | Biodegradable? |
|---|---|---|---|---|
| Standard nylon | Nylon-6,6 / PBT | Yes | Yes (confirmed) | No |
| Charcoal nylon | Nylon + charcoal infusion | Yes | Yes (confirmed) | No |
| Plant-based bioplastic | PA11 / PA10,10 / PLA | No (plant-derived) | Likely (not yet fully studied) | Partially, under specific conditions |
| Horsehair | Natural animal hair (keratin) | No | No | Yes, fully |
This table is not here to make you feel bad about the choices you've made up to now. Most people have never been given this information. The industry has no incentive to share it, and the marketing around toothbrushes focuses almost entirely on bristle softness, head shape, and whitening claims — never on what the bristle is chemically made of.
Now you know. And knowing means you can choose differently.
What to Look For When You Buy a Natural Toothbrush
If you're switching away from nylon bristles, here's a simple checklist:
- The bristles should be listed as natural animal hair — specifically horsehair or boar bristle. If the packaging says "nylon," "soft nylon," "plant-based nylon," or doesn't mention the bristle material at all, assume it's petroleum-derived.
- The handle should be bamboo or wood — not plastic, not recycled plastic. Bamboo is the gold standard: fast-growing, no pesticides, fully compostable.
- The packaging should be plastic-free — kraft paper, cardboard, no plastic wrap or plastic windows. This often signals that the brand is thinking about the full lifecycle of the product, not just the handle.
- The brand should be transparent — if a company isn't willing to tell you exactly what their bristles are made of, that tells you something.
One more thing worth knowing: even the parts of the toothbrush that aren't the bristle matter. KYND's bamboo handle is coated in 100% natural beeswax — not synthetic lacquer, not chemical sealant — which prevents moisture absorption and mold without introducing any synthetic material to the brush. The packaging is fully biodegradable kraft cardboard with no plastic windows or coatings. The entire product, from bristle to box, is designed to leave nothing synthetic behind. (More on what "fully biodegradable" actually means in practice.)
The Bottom Line
The toothbrush industry has been running on the same petroleum-derived material for nearly 90 years. The marketing has evolved — softer branding, bamboo handles, charcoal coatings, plant-based claims — but for most products, the bristle chemistry has barely changed.
You deserve to know what you're putting in your mouth. And once you know, the choice is a simple one.
Natural bristles exist. They work. They've worked for centuries. And they don't leave a trail of synthetic polymer fragments in your body every morning.
Try KYND's natural horsehair bamboo toothbrush — 4 brushes, fully natural, fully compostable. Available at trykynd.co
References
- Azoulay, D. et al. (2024). Preliminary results on microplastic release from commercial toothbrushes during simulated brushing. Microchemical Journal. sciencedirect.com
- Aragaw, T.A. (2023). Microplastic release from bioplastic (PLA) materials. Journal of Hazardous Materials.
- White, C.M. et al. (2023). Antibacterial properties of activated charcoal toothbrush bristles. Journal of Dental Research.
- I'm Plastic Free (2026). 4 Microplastic Free Toothbrushes Made with Bamboo and Natural Bristles. implasticfree.com
- DuPont Company History Archives — Introduction of nylon, 1938.