What Are Quats in Hair Care? Polyquaternium, Behentrimonium & What They Do
Quats are why your conditioner makes hair slip, soften, and stop flying away with static. But they range from gentle and biodegradable to build-up-prone and tough on waterways. Here's how the main ones compare.
Key takeaways
- Quats (quaternary ammonium compounds) are positively charged ingredients that bind to negatively charged hair, creating softness, slip, and anti-static.
- Conditioning quats like behentrimonium and cetrimonium do the smoothing; polyquaterniums form a film for frizz and humidity control.
- Gentlest on hair and water: behentrimonium methosulfate and esterquats, which are readily biodegradable.
- The trade-offs: some polyquats build up, leave-on quats can irritate sensitive scalps at high levels, and small monomeric quats can be tough on aquatic life.
- Natural swaps - plant-based cationics, fatty alcohols, oils, and botanical gels - condition more gently, and Hairmony can filter quats out of your recommendations entirely.
Flip over almost any conditioner, detangler, or 2-in-1 shampoo and you'll find a quat - short for quaternary ammonium compound.
What are quats?
A quat is a molecule built around a nitrogen atom carrying a permanent positive charge, attached to one or more long fatty chains.
Healthy hair carries a slightly negative charge on its surface - more so when wet or damaged. Opposite charges attract, so quats cling to hair even after you rinse, their fatty tails lying flat along the strand like a lubricant.
It's also why shampoo and conditioner are usually separate steps: most cleansing surfactants (like sulfates) are anionic - negatively charged - while conditioning quats are cationic.
Why your conditioner is full of them
That thin cationic layer changes how hair behaves:
- Slip and detangling - strands glide past each other instead of catching, so combing and day-to-day friction cause less breakage.
- Anti-static - the charge neutralizes the frizzy "halo" you get in dry air.
- Softness and shine - a smoother cuticle reflects more light.
As a rule of thumb, the longer the fatty chain, the richer the conditioning.
The quats you'll see on labels
Conditioning quats (the "-monium" family)
The classic smoothing agents, named after their fatty chain length:
- Behentrimonium chloride / methosulfate - a 22-carbon chain from rapeseed oil. The longest chain here, so the richest slip; a favorite for thick, curly, and coily hair.
- Steartrimonium chloride - an 18-carbon chain. Medium-weight conditioning and softness.
- Cetrimonium chloride - a 16-carbon chain. The lightest of the three; great for everyday detangling and anti-static on finer hair.
You'll often see the same molecule as chloride or methosulfate - identical conditioning part, different balancing ion. The methosulfate version is the milder, more eco-friendly one.
Polyquaterniums (the polymers)
Polyquaterniums are large cationic polymers, identified by a number (Polyquaternium-7, -10, -11, and so on). Instead of a single fatty tail, they drape a thin film over the hair - excellent for frizz, humidity resistance, and a smooth finish - and appear in shampoos, conditioners, and styling products alike.
- Polyquaternium-10 - a cationic cellulose, plant-derived (typically from wood). Adds anti-static, moisture retention, and smoothness; heavier grades can build up.
- Polyquaternium-7 - a synthetic polymer with a strong, substantive film. Loved for curly and coily hair, but more prone to buildup.
- Lighter polyquats (such as Polyquaternium-6 and -37) condition with much less buildup, which suits fine hair.
Antimicrobial quats (the preservatives)
A third group - benzalkonium chloride, cetrimonium bromide and similar - isn't there to condition at all: it kills microbes and preserves formulas, the same chemistry found in disinfectants. These carry the most irritation and environmental baggage of any quats, so they're worth noticing on a label, especially in leave-on products.
Quat by quat: hair, scalp & environment
Here's how the most common quats compare:
| Ingredient | What it is | Hair benefit | Scalp & skin | Environment |
|---|---|---|---|---|
| Behentrimonium methosulfate | C22 quat, rapeseed-derived | Rich slip; ideal for thick & curly | Mild, low irritation | Readily biodegradable; doesn't bioaccumulate |
| Behentrimonium chloride | C22 quat, chloride form | Strong conditioning, similar slip | Slightly harsher; limited in leave-ons | Less readily biodegradable than methosulfate |
| Cetrimonium chloride | C16 quat | Light conditioning & anti-static | Safe rinse-off; keep leave-on low | Aquatic-toxicity concern at high loads |
| Steartrimonium chloride | C18 quat | Medium conditioning, softness | Similar to cetrimonium | Similar to other alkyl quats |
| Polyquaternium-7 | Synthetic cationic polymer | Film for frizz & humidity control | Generally well tolerated | Polymer; resists breakdown, can persist |
| Polyquaternium-10 | Cationic cellulose (plant-based) | Anti-static, smoothness, moisture | Generally well tolerated | Plant backbone; heavy grades build up |
| Benzalkonium chloride | Antimicrobial quat (preservative) | Not a conditioner | Higher irritation/allergy risk | Aquatic toxicity & resistance concerns |
Are quats safe for your scalp?
For most people, the conditioning quats in rinse-off products are well tolerated.
The nuance is concentration and contact time: the Cosmetic Ingredient Review found cetrimonium chloride safe in rinse-off products at up to around 10%, but only up to 0.25% in leave-on products - above that, it can irritate or sensitize skin. That's why well-formulated leave-in conditioners keep quat levels low.
Sensitive, eczema-prone, or reactive scalps are the exception: quats are a known cause of irritant and allergic contact dermatitis, with the antimicrobial ones the most common culprits. If your scalp flares with a product, the ingredient list is worth a closer look - and so is your overall scalp health.
Tip: This is general education, not medical advice. If your scalp is persistently itchy, flaky, or inflamed, patch-test new products and see a dermatologist - a reaction can mimic an unrelated scalp condition.
One often-exaggerated point: antibiotic resistance. Heavy use of antimicrobial quats in disinfectants has been associated with bacterial tolerance - a cleaning-product and hospital concern, not your conditioner - but it's a fair reason not to overuse antibacterial, quat-based leave-on products at home.
The environmental side
Quats are drawing growing scientific attention as a class of emerging environmental concern. The headline issues:
- Aquatic toxicity - some small monomeric quats are acutely toxic to certain aquatic organisms at low concentrations.
- Persistence - quats bind strongly to sludge and sediment and resist breakdown without oxygen.
Context matters, though: the bulk of the quat load reaching wastewater comes from disinfectants and cleaners, not hair products - a gap that widened during the pandemic's surge in surface cleaning.
Esterquats - quats built with a breakable ester bond - are readily biodegradable, hydrolyzing into a harmless fatty-acid soap and a small water-soluble fragment. Behentrimonium methosulfate is likewise readily biodegradable and non-bioaccumulative. Choosing these forms is the simplest way to keep a routine lighter on waterways.
Natural alternatives to quats
Skipping quats is doable - natural swaps just trade a little detangling muscle for gentleness and biodegradability. Here are the best options, from closest match to gentlest:
Plant-based cationic conditioners (the closest swap)
A new generation of non-quat, plant-derived cationics condition almost like the real thing while staying readily biodegradable and gentle on aquatic life:
- Brassicyl isoleucinate esylate (with brassica alcohol) - a rapeseed/mustard-derived, quat-free cationic that behaves much like behentrimonium. Often Ecocert- or COSMOS-certified.
- Amino-lipid conditioners - cationic agents built from plant amino acids and fatty alcohols, designed as a near one-to-one quat replacement.
- Cationic guar and inulin polymers - plant-derived film-formers that stand in for polyquaterniums in rinse-off products.
Fatty alcohols & plant lipids
- Fatty alcohols (cetearyl, cetyl, behenyl alcohol) - the emollient base of most "natural" conditioners. They soften and add slip, with less anti-static punch than a quat.
- Oils & butters (jojoba, argan, shea, coconut) - seal the cuticle and cut friction. Great for thick or coily hair; use sparingly on fine hair to avoid weighing it down.
Botanical slip & humectants
- Botanical gels - marshmallow root, slippery elm, and flaxseed are rich in mucilage that gives genuine detangling slip.
- Aloe vera and glycerin - lightweight humectants that soften and smooth.
- Hydrolyzed proteins (rice, wheat, silk) - add a light strengthening film and improve manageability.
Reality check: If your hair is very tangly or coily, you may need to layer natural conditioners (oil plus a botanical gel) to match a quat's slip - or lean on a plant-based cationic for the best of both worlds.
How to read a label
You don't need to avoid quats - just match the right ones to your hair and priorities:
- Everyday softness & detangling: behentrimonium methosulfate or cetrimonium chloride in a rinse-off conditioner are reliable, well-studied picks.
- Thick, curly, or coily hair: longer-chain behentrimonium quats plus a film-forming polyquaternium give the most slip and frizz control.
- Fine or buildup-prone hair: lean on lighter quats (cetrimonium) and low-buildup polyquats (Polyquaternium-6 or -37), and clarify now and then.
- Sensitive scalp: favor rinse-off products, keep leave-on quats low, and skip antimicrobial quats in anything you don't wash out.
- Eco-minded: look for methosulfate forms, esterquats, and plant-derived cellulose polymers.
Which quat suits you comes back to your hair itself - its porosity, thickness, and curl pattern, most of which are written into your genetics. That's what Hairmony reads from a photo, so the products it recommends fit your real hair instead of a guess - and if you'd rather avoid quats altogether, it can filter them out of your recommendations entirely.
Frequently asked questions
Are quats bad for your hair?
No - conditioning quats are what make hair soft, detangled, and static-free. The main downside is that some polyquaterniums can build up on the strand over time, especially with sulfate-free or co-washing routines. An occasional clarifying wash removes the buildup.
What's the difference between behentrimonium chloride and behentrimonium methosulfate?
Both share the same plant-derived conditioning molecule and differ only in the ion that balances its charge. Behentrimonium methosulfate is the milder, more readily biodegradable form, while behentrimonium chloride is a slightly stronger conditioner that's limited to low concentrations in leave-on products.
Do polyquaterniums build up on hair?
Some do. Heavier polyquaterniums such as Polyquaternium-7 and high-molecular-weight Polyquaternium-10 grip the hair tightly and don't fully rinse away, so they can build up - even though they're technically water-soluble. Lighter polyquats like Polyquaternium-6 build up far less. Clarifying occasionally keeps it in check.
Are quats safe for the environment?
It varies by type. Small monomeric quats can be toxic to aquatic organisms and bind strongly to sludge and sediment, where they resist breakdown. Esterquats and methosulfate forms are readily biodegradable and far gentler on waterways. Most environmental quat pollution comes from disinfectants and cleaners rather than hair conditioner.
What are natural alternatives to quats?
Plant-based cationic conditioners like brassicyl isoleucinate esylate and amino-lipid agents come closest, behaving much like quats while staying readily biodegradable. Gentler options include fatty alcohols (cetearyl, behenyl), plant oils and butters, and botanical gels from marshmallow root, slippery elm, or flaxseed. They condition more softly than synthetic quats, so very tangly or coily hair may need to layer them for the same slip.
How do I know if my shampoo has quats in it?
Scan the ingredient list for names ending in '-monium' such as behentrimonium, cetrimonium, or steartrimonium, or starting with 'Polyquaternium' followed by a number. Guar hydroxypropyltrimonium chloride is a plant-derived quat too. They usually sit in the middle of a conditioner's ingredient list.
Keep reading
The Hairmony Team
We're the team behind Hairmony - the app that reads your hair and scalp from a photo and builds a routine around it. We write these guides to make the science of hair care simple and actually usable.
Confused by ingredient lists?
Hairmony reads your hair from a photo and matches products to your real profile - and if you want to skip quats, it can filter them out completely, so every recommendation comes back quat-free.
Try Hairmony free for 3 days →