The standard test for a good hair cleanser is how much 'soil' or build-up it leaves behind after you've used it.
Co-washes leave behind a lot of soil -- which makes them less reliable at getting your hair hygienically clean.
How effective is co-washing right now?
For Camille, tossing her clothes into the washing machine, then showering and washing her hair are a no-brainer when she gets in from her shift at the local clinic. The part she's not sure of is what she should use to wash her hair. "Does co-wash count as washing right now," she asks. "Can it get my hair properly clean?"
Probably not. While co-washing — short for washing your hair with conditioner — definitely has its place in the natural hair toolkit, it has its limitations, too. We break down 7 of them and how they get in the way of having hygienically clean hair.
Clean hair: how the best cleansers work
The secret to clean hair starts with a process hair scientists call 'roll up'. All good cleansers use this process, which helps water get in between the buildup and your hair and start to roll it up off your strands.
That attraction pulls water into the strand, pushing up the oily film and causing it to roll up on the surface. Once it's there, the surfactants' micelles grab the grease, making it easy to rinse away.
Anionic or negatively-charged surfactants excel at this. The positive or cationic surfactants in co-washes aren't quite as good at the rinsing away part. This is why:
All co-washes leave build-up. They're designed to.
Cetrimonium chloride, stearylkonium chloride, behentrimonium methosulfate. . . You've probably seen these on the back of some of your favourite products. They're three of the most popular positively-charged surfactants, used widely in co-washes and conditioners.
As well as their conditioning chops, these ingredients also have some detergent qualities, which is why you can co-wash with them. But they weren't designed for that.
Conditioning surfactants are formulated to be mostly rinsed away -- and to leave a little something behind. That's cool if you're trying to co-wash healthy hair. It's easier to rinse the conditioner away when you're done, which will maximize how clean you can get your hair.
The secret to clean hair is a cleanser that causes good roll-up. Image by Huha Inc.
But if your hair is even slightly damaged, more conditioner will be deposited onto your strands, staying there days after you thought you rinsed it out.
That's because the positively-charged conditioning agents are designed to bind to the negatively-charged spots of damage on your hair.
If you have extremely damaged strands, the negative charge is even stronger. It's going to make sure those positively-charged conditioning ingredients stick around in pretty large quantities.
That's great for protecting fragile, sensitized hair. It's not so good for getting your hair clean. This is why strands will often look or feel 'coated' after they've been co-washed: not clean.
If it was just conditioner residue on your hair, like what happens when you condition after shampooing, that would be cool. But when you're trying to wash dirty hair with something that can't help but stick to your hair, then all sorts of undesirables can stick around in that residue, too. From dirt to dust to pollution, and possibly microbes, too.
The harder the water, the greater the amount of fatty substances from your co-wash, or even your scalp's own natural oils, that will stick to your hair. Those lipids provide a bridge for metal ions in the water to bind to your strands, creating more buildup that's hard to shift. Removing it will require the use of harsher cleansers, multiple times.
In other words, the opposite of what you're trying to achieve by using conditioner to wash your hair.
Co-washing doesn't work on really dirty hair
A lot of No-Poo devotees push the idea that when you co-wash, all the dirt washes off your hair, while the conditioning ingredients and your own natural oils stay on. So you get all of the good and none of the bad. If only it were so. What actually happens is a lot messier. Some of the dirt and most of the conditioner gets rinsed away.
But the conditioner that stays behind can form a matrix on the hair with all the rest of the dirt trapped inside it.
This is why co-washing works best on hair that is already pretty clean, the type of hair that gets co-washed daily or every other day, or as a stopgap between regular shampoos.
The ideal co-wash candidate is also someone who doesn't use products that cause a lot of soils to build up on their hair. Since some residue inevitably gets left behind, you don't want it to be too much.
Getting that balance right also means being extremely savvy about ingredients — and not just silicones, sulfates and mineral oil. Buildup can also come in the form of 'CG-friendly' ingredients like behentrimonium methosulfate, the strongly positively-charged, long chain quat that's in almost every creamy product for curly hair.
If you use leave ins, curl creams or heavier co-washes, you probably have some of this co-wash resistant residue in your hair.
Purpose-built co-washes make getting your hair clean even harder
Old school co-washes were just dollar conditioners.
They weren't meant to be cleansers, but their minimalist formulas using the most simple cationic and nonionic surfactants made them so.
To save money, manufacturers kept the ingredients list short and the concentration low.
This meant minimal residue was left on strands after rinsing, making them great for cleansing, if not conditioning.
But then came the new, purpose-built co-washes.
They took all the work out of trying to figure out which drugstore conditioner was safe to conditioner wash with. And they upped the conditioning ingredients, making them thicker, richer and more decadent by far.
Today, co-washing your hair can be a real life, luxe experience.
There's just one problem.
They don't clean your hair that well.
Co-washing with heavy modern cowashes often leaves a lot of residue on hair. Image by Hannah Xu.
The unnecessary inclusion of oils, gums and exotic-sounding extracts makes the formulas bloated and heavy, less able to actually clean your hair.
But the biggest problem is the buildup the co-washes themselves create.
Increasing the concentration of conditioning surfactants means there's more to be left behind after you rinse.
Plus, these co-washes add new types of residue thanks to the aforementioned extra ingredients. . . and because they tend to be based on behentrimonium methosulfate.
Called BTMS for short, it's an excellent conditioning ingredient but way too substantive to the hair to be used as the main cleansing agent. All this means most modern co-washes are more like a thick conditioner than a cleansing one.
Little wonder that even before we were in a pandemic, most of these co-washes were not getting your hair clean enough.
Co-washes can't get pollution off your hair
Right now scientists are looking at the role pollution has to play in this pandemic.
They already know that virus-containing aerosols are able to hop up on pollution particles and use them to travel far and wide — much further than the recommended 2 metres social distance.
So now they're trying to figure out if those aerosols are still a threat after flying tens, if not hundreds, of metres away.
In the meantime, you probably don't want to be walking around with that stuff in your hair.
Pollution has long been shown to damage your hair and your overall health; it can even turn your hair grey. So you need something that can grab that particulate matter, pull it off your hair and send it swirling down the drain.
Pollution can be damaging to your hair. Image by AJ Nakasone.
It isn't easy.
The tiniest pollution particles, those under 0.1nm, are really hard to remove, but you can shift the slightly larger ones with anionic surfactants like sodium laureth sulfate or ammonium laureth sulfate.
A co-wash can't do any of that for you; these types of particles won't bind with the cationic surfactants in conditioner. So while co-washing can remove a lot of chunkier, visible grit and dirt (because of the slip it creates), it doesn't have what it takes to remove pollution particles you can't see, which can bind very strongly to your strands.
Stuff like soot, hydrocarbons and heavy metals like lead aren't moving from your hair unless they're made to, by a more robust cleanser.
Proper cleansing with a co-wash depends on how good you are at scrubbing
The surfactants in conditioner are weak.
They need all the help they can get in picking up oily stuff. So you have to be a pro at getting them to solubise the gunk on your hair, creating a nice emulsion to bind all the dirt with the water you're trying to use to rinse it away.
That can be tricky. Getting it right involves using the right amount of conditioner, having the right amount of water on your hair, at the right temperature, spending the right amount of time, and having a good lathering technique.
Then and only then can you work that co-wash into a dense, but low-foaming lather and get a decent cleanse, removing the kinds of build-up that co-washes can remove.
Not everybody knows how to do all that.
Conditioner rinses off with little lather. Image by Mr Karl
Many people apply a co-wash the same way they'd apply conditioner, thinking it's magically going to get their hair clean. That's not the way it works.
Your scrub technique is at least as important as your cowash's ingredients. And for people who don't have a lot of hand or arm strength, or a lot of time, that makes a successful co-wash difficult to achieve.
Does all this mean co-washing doesn't work?
No, co-washing does still have benefits for your hair. It can provide mild cleansing in between shampoos, it often works as a great pre-poo step for tangle-prone hair and it's a good way to rehydrate your hair.
It's just not the move when you've spent time in a highly exposed environment, with a high density of dangerous microbes or pollution particles, when you've used a bunch of buildup-prone products, or when you use it as your sole or main cleanser. Conditioner doesn't clean reliably well enough for that.
So what kinds of cleansers for natural hair do you recommend instead of co-washes?
Here's what should be on your checklist when you're looking for a good cleanser for natural hair:
One, it should be versatile enough to pick up both oily soils, like sebum, plant oils and silicones, and particulate soils like dust, dirt and bits of pollution. Anything that can get the oily soils will generally be able to remove menaces like envelope viruses, which have a lipid coat.
Two, it needs to be able to pick up metal ions to help you scrub off a lot of the pollution and hard water buildup. You also want it to be able to remove residue from cationic surfactants, which can be the hardest to remove. In most cases, a cleanser that can do all this work will be a shampoo.
What about clays? Or soaps?
Clays are good at picking up oils and some mineral deposits but struggle with many modern cosmetic ingredients. Soaps are good for washing our hands, but tests show they're less effective at removing soils from hair. Plus, their high pH can be extremely damaging to the cuticle.
What kind of shampoo is better, sulfate or sulfate-free?
Both sulfate and sulfate-free shampoos can get your hair clean.
It depends on what, or how much you need to remove.
Anionic surfactants are the all-rounders. They're the ones that can shift oils, petrochemicals, silicones, dirt, pollution and other types of debris commonly found in hair.
The most widely used anionic surfactants are sulfates. One popular anionic, olefin sulfonate, isn't a sulfate, but beware: it is just as harsh as sodium lauryl sulfate. Modified 'ether' sulfates like sodium laureth sulfate or ammonium laureth sulfate are much safer anionic cleansers, as are the sarcosinates.
Some good shampoos based on anionic surfactants include the peppermint-y, jelly textured atrActiva Anti-Stress Shampoo, which is a deep cleanser, and Silicon Mix Shampoo, a creamy, conditioning shampoo.
Anionic surfactants like the laureth sulfates are excellent cleansers. But that doesn't mean they're your only choice, especially if you have to shampoo frequently.
Many low-poo or sulfate-free shampoos are based on amphoteric surfactants, which have a dual, positive-negative charge, or nonionic surfactants with no charge.
These ingredients tend to be less powerful than the most common anionic surfactants, but if your hair is just moderately soiled and doesn't need clarifying, several of these ingredients can handle it.
Two of the most widely used milder surfactants include cocamidopropyl betaine, an amphoteric surfactant which is a popular secondary surfactant, and the nonionic decyl glucoside.
In sulfate-free cleansers, they form part of the complex surfactant blends necessary to replace the multifunctional sulfates. You can find cocamidopropyl betaine for instance, in Halka Baba de Caracol Sulfate-Free Shampoo helping to create a rich, dense lather that rinses clean, something that's crucial for low porosity hair which is sensitive to buildup.
Whether co-washes could possibly remove coronavirus from your hair remains to be proven. Without those tests, we only have what we know about co-washes' cleansing performance — and the evidence in favour of more robust cleansers to go on.
For now, erring on the side of caution and using the types of cleansers that are known to work against microbes and which can roll up most unwanted residue from your hair sounds like the smartest move.