Fact-check: What is micellar water and how does it work? An Update

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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. This also comes in video form – check it out here! There are tons of micellar …

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How Do Bath Bombs Work? The Science (With Video)

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Bath bombs are awesome balls of fizzy goodness, with some interesting science behind them! They were invented in 1989 by Mo Constantine, one of Lush’s founders. Bath bombs contain the chemical sodium bicarbonate, also known as baking soda, as their key ingredient. This is the text version – scroll down for the video! Some of you might remember that baking …

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Do peeling gels really peel off my skin? (with video)

“Is all the stuff that rolls off with a peeling gel really my skin?“ This is a question I come across a lot! In case you’ve forgotten, a peeling gel is a popular type of cleanser in Asia. You start off with a watery gel like this, which you spread over your face (the one picture here is Laneige Strawberry …

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How to Use Comedogenicity Ratings (with Video)

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You’ve probably seen a comedogenicity chart like these ones (and the one further down the page) before, rating different ingredients on their ability to cause pimples. Supposedly you check the ingredients list of your product against the comedogenicity list. If it has highly comedogenic ingredients, it will cause pimples, if it doesn’t, then it won’t. It’s simple, systematic and foolproof, right? …

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Why You Shouldn’t Use Lemon Juice on Your Skin

There are more DIY skincare recipes on the internet than you can shake a stick at, and most of them really, really like lemon juice. According to these DIY tips you should be slathering it all over your face and hair. Lemon juice smells nice, and it’s pretty cheap. But is it effective? And is it safe? Let’s talk about …

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Activated Charcoal in Skincare: The Science

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Activated charcoal skincare products are pretty cool. They’re black, they’re sciencey-sounding and they’re said to suck dirt out of your pores like a magnet – what’s not to like? The reality is a little more complex than that…

(If you’re after the video version of this post, check it out here! To make sure you don’t miss a video from me when it goes live, click here.)

What is activated charcoal?

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Activated charcoal is carbon soot that’s been treated to give it a sponge-like structure, with lots of holes. If you zoom into activated charcoal, it’s very jaggedy, giving it a huge surface area. It’s estimated that 1 gram of activated charcoal has a surface area of 3000 square metres, which is the same as 3 Olympic swimming pools, 7 basketball courts or 230 car parking spaces.

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This gigantic surface area is particularly handy for soaking up substances. You can see how effective it can be for purifying water in the picture underneath, where activated charcoal’s grabbed onto all the red dye in the glass on the left (it can also be seen with the orange fizzy drink in the video).

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In medicine, activated charcoal is mostly used in poisoning cases, where a large dose is fed to the patient alongside other treatments. A lot of the poison sticks to the charcoal instead of absorbing into the body.

Since it’s a default treatment for soaking up ACTUAL TOXINS in poisoning, lots of people eat/drink activated charcoal for “detox” purposes, which sounds like it could work (although if you read my other blog, you’ll know that detox is a scam). You might be wondering, how does activated charcoal tell the difference between good things and bad things? The answer is… it doesn’t.

How does activated charcoal work?

At a molecular level, things are sticky. It’s why the wax in a candle stays together as one big clump instead of splaying everywhere, and why you have to put in a whole heap of heat to get water molecules to separate and turn into steam. This stickiness is known as intermolecular forces – interactions that stick molecules together. Without them, everything would be a gas.

There are a few types of intermolecular force – the one that activated charcoal uses is called dispersion forces. Absolutely every substance has dispersion forces, whether it’s a vitamin or a poison.

Remember the large surface area that activated charcoal has? This means there’s a lot of space for things to stick to. And since everything can form dispersion forces, activated charcoal actually soaks up all sorts of things, including nutrients like vitamins, meaning you don’t get the full health benefits of your food.

Activated charcoal can stick to medications as well, if they’re still in your digestive system. This means that you might not be getting the right dose.

In a poisoning situation, you’re probably not worried about whether you get enough vitamins, but in everyday life it’s not such a good idea to prevent your body from taking up random nutrients and medications on a regular basis. So don’t make activated charcoal part of your regular diet!

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What is thermal water and how does it work in skin care?

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If you walk into a pharmacie in France, you’ll immediately bump into a giant display of thermal water spray cans. A whole host of French skin care brands like Avène, La Roche-Posay, Uriage and Vichy sell thermal water sprays. What is it, what’s in it, what does it do and how is it different from regular water?

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What is thermal water?

Thermal water comes from hot springs. The water in these hot springs come from deep in the ground, where it’s heated by geothermal activity (the Earth’s natural heat which also causes lava to be molten).

What’s in thermal water?

It’s mostly water, of course, but it isn’t “just water in a can”! As the thermal water rises to reach the spring, it passes through rocks and soil which dissolve to add minerals to the water. The mineral content of a particular thermal water depends on where it comes from. The minerals include the ones found in your skin’s natural moisturising factor (NMF), like chlorides, sodium, potassium, calcium, and magnesium.

Here are the compositions of the 4 most popular thermal waters (source: Bacle et al., Int J Dermatol 1999, brand marketing materials). There’s some variation between batches of course, since it’s a natural mixture.

Composition (mg/L or ppm)AvèneLa Roche-PosayVichyUriage
Total dry residue207444512011000
Sodium4.81018602360
Potassium0.72.299.645.5
Calcium42.7140150.6600
Magnesium21.24.912.3125
Chlorides5.4253573500
Bicarbonates226.73964776.3402
Sulfates1430Trace2862
Nitrates1.4TraceTrace< 100
Silica (SiO2)10.630-42
Selenium-0.060--
Strontium-0.260--
Zinc-0.022-0.16
Copper-0.005-0.075
Manganese---0.154
Iron---0.015
pH7.46.97.006.77

As you can see, the composition varies a fair bit, with Uriage, the thermal water with the highest mineral content, being 55 times more concentrated than Avène, which has the lowest mineral content.

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Residue remaining after room temperature evaporation of 10 mL of Uriage Thermal Water in a 250 mL beaker.

“-” in the table means no data, since different thermal water brands like to highlight different aspects of their water. La Roche-Posay talks a lot about the selenium content of their water, while Uriage emphasises the high calcium concentration. Avène talks a lot about the 2:1 ratio of calcium and magnesium in their water.

There’s also nitrogen gas inside the can that acts as a propellant, to push the water out as a spray. Paula’s Choice writes that the nitrogen “can generate free-radical damage and cause cell death”, which luckily isn’t true, since nitrogen gas (N2) make up 78% of the air we breathe! It’s actually very unreactive, so unreactive that it’s commonly used in laboratories to flush out more reactive things like oxygen and water. (The papers cited in the Beautypedia article actually involve chemicals that just contain nitrogen atoms, not nitrogen gas itself.)

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