Over the past two years, my post on the chemistry of micellar water with dodgy photographed scrawlings has become one of the most popular, so I thought it was high time to update it with nicer drawings and finetune the explanation of the science.
There are tons of micellar waters on the market now, many of them with similar active ingredients.
The essential ingredients in any micellar water are:
- Water (obviously) and
- One or more surfactants.
Surfactants are cool ingredients that I’ve written about a lot (including in my guest post on The Toast). They’re useful molecules with a hydrophilic head that’s attracted to water (and repels oil), and a lipophilic tail that’s attracted to oils and grease (and repels water).
Oil and water normally repel each other, so they try to stay away from each other. This means that oil doesn’t dissolve in water (which you’ll know if you’ve ever tried to wash an oily dish), and instead sits on top like a bad toupee.
When surfactants are added to an oily dish, for example, and then scrubbed with water, they help it break up into droplets (emulsion droplets). They surround the oil and “hide” it from the water, allowing it to be smuggled out and washed away to leave a clean surface.
Surfactants are the key ingredients in micellar water, as well as in detergent, soap, shower gel, face wash, shampoo and so on. You’ll also find them keeping oil and water happy together in emulsion products like moisturisers and mayonnaise.
So let’s get back to micellar water. When enough surfactant is added to water (more than something called the critical micelle concentration or CMC), the surfactant molecules assemble themselves into clusters called micelles.
These micelles are spherical arrangements of surfactant molecules, with the tails pointing in and the heads facing out – this means the hydrophobic tails are protected from the water by the hydrophilic heads.
Some brands of micellar water contain oily substances, like Nivea Sensitive 3-in-1 Cleansing Water which contains grape seed oil. In these products, the oily substance will sit in the middle of the micelle, like in the emulsion droplet.
(In my previous post, I labelled the emulsion droplet a micelle – I’ve been told by a materials chemist I work with that that’s incorrect.)
The micelles aren’t bound together into a molecule, which means they’ll rearrange easily. If the micellar water is poured onto a cotton wool pad, for example, it rearranges so that the heads are stuck to the cotton wool (made of cellulose, which is hydrophilic), and the tails stick out (the technical term for this is an oriented monolayer).
This means there’s a neat oil-loving layer sitting on your cotton wool pad. Since make-up, sebum, grease and dirt are all oily, this means it’s perfect for cleaning your face at the end of the day.
Here’s what it looks like on a microscopic scale (diagrams are really really not to scale):
When you wipe off the make-up with the cotton pad, the layer of lipophilic tails absorb the oily make-up. Since it’s only one layer of tails, you might need to go through a few pads to get rid of everything if you’re wearing thick make-up or you’re super greasy. If you don’t rinse your face afterwards, you’re also likely to have bits of micellar water left on your face afterwards.
This leads to one of the most common questions I’m asked: Do you need to rinse your face after you use micellar water?
Sadly, the answer to this question is a non-committal, unsatisfying “it depends”.
Micellar water contains mild surfactants, and surfactants can disrupt the structure of the skin – sodium lauryl sulfate, for example, is a strong irritant. But not all surfactants are made equal.
Like how some people can’t tolerate any sodium lauryl sulfate on their skin while others can use it daily for years with zero problems, some people will be able to tolerate the surfactants in micellar water better than others. And just to make it even more complex, there’s a range of surfactants used in different micellar water products, with different irritancy potentials.
If your skin feels dry or itchy after using it, I would definitely recommend following the micellar water with a wipe of a cotton pad soaked in plain water.