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How do Clay Masks Work? + Science of WHY it’s good for your skin

by | Last updated Feb 16, 2020 | Published on Feb 10, 2019 | How Clay Works

Clay has an abundance of benefits and when infused into your skin care regime can provide a host of awesome results. But if you are like me, you don’t just apply anything to your skin because someone told you too.

In fact, I spent some time looking through the first page of articles on Google, and found that not one of the articles actually told me how clay works for my skin, but only about the benefits and which kind of clay to try.

I put my nerdy glasses on, got my research gloves out and rolled out my photoshop.  (hopefully) making it easier to understand the science behind how clay masks works for your skin, and how clay can be beneficial.

So how do clay masks work?

Clays are a result of 3 things, chemistry, geology, and physics.

Science of Clay: How do clay masks work? Chemisty | Physics | Geology
The shortest answer, and keep reading for wayyyyy more information to this vast topic, is that clays are negatively charged minerals, and when applied to your skin, do an exchange of removing impurities aka toxins, chemicals, bacteria from your skin and leaving behind minerals.

In short, takes away the bad, leaves the good.

Most clays are found in mineral clay deposits on or just below the earths surface.  Any type of soil does not make it a clay.  Each clay is classified by their mineral content, and that’s why each different type of clay provides a different benefit to your skin.

Clay Mineral Deposit on Surface of Mountain

The benefits to your skin after a clay mask are actually pretty amazing, it can fight acne, reduce the appearance of pores, give you a super deep clean by removing impurities from your skin, balance your complexion, help with oily skin, and rejuvenate your skin with minerals. 

The benefits are a whole other topic altogether.  I put together the definitive guide to bentonite clay and kaolin clay here.

The benefits do extend beyond use as only a clay face mask, clay has been beneficial in use as a poultice to heal burns, bites, and sores, or to rejuvenate and clarify hair, as a whole body detox in a detox bath, and some people even eat the clay.  Do not eat our clay, it is not edible food grade. 

The coolest thing about doing a clay face mask, is that it’s 100% natural.  It’s just a special dirt.  You can find our signature clay recipes here.

Get 9 of my favorite bentonite clay recipes or kaolin clay mask recipes.

Some people, have named these clays, healing clays because of their ability to heal our bodies. 

What are the Different Types of Clay?

There are approx 30 different types of clay, not all are used in cosmetics.  In fact clay has a lot of other uses, just a few of those are clay pottery, construction products, oil drilling, and water purification systems.

Find our comprehensive guide to all the types of cosmetic clays.

A clay is defined as an earthy material that has a very small particulate size (less than 2 micro-meters in size).  That’s 2000 times smaller than a millimeter.  Kaolin clay is slightly larger particulates, less than 5 micro-meters.

How small is a particle of clay? 2 micrometers or less

To understand clay and how it works, we learned about the crystal structure of the clay and the surface chemistry in water suspension.  The next section shows the crystal structure of the clay and how they are classified.

4 types of Clay Mineral Groups:

If you are a visual person, scroll down to our easy to read infographic for the types of mineral groups.

  • Kaolinite – This is the clay group that is most popular (by the name I’m sure you guessed it), Kaolin.  Kaolin is well known as a pure white clay, but there are actually a couple different variations depending on the minerals and color, the second most well known kind is Rose Kaolin. Minerals found in Kaolinite are:
    • kaolinite
    • dickite
    • nacrite
    • halloysite
  • Smectite – The clay mineral group of the popular Bentonite Clay but also Fullers Earth, Rhassoul, and Glacier clay. Smectites include:
    • montmorillonite
    • nontronite
    • vermiculite
    • sapnite
    • talc
    • sauconite
    • nontronite
    • pryophyllite
    • beidellite
  • Chlorite – It’s disputed whether chlorite’s are considered a clay mineral.  They tend to be harder mineral rocks.
  • Illite – the clay mineral home of our family of beloved french clays.  French clays can be found in different color and mineral variations, including green, yellow, red and pink.

Clay Mineral Groups and types of Clay in Each - Infographic

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How is Clay Classified?

When a deposit is found, there are a couple criteria that a clay must meet to be classified.  The first is the particle size, being <2 micro-meters.

To classify which mineral group a clay fits into the particle structures are used to determine this.

This is a little in-depth, but hey, these were all questions that I found interesting when discovering how does clay work, what clay is made of, and where clay comes from.

Here we go!

A clay mineral is classified in a 1:1 or a 2:1 ratio sheet.  They are fundamentally built of tetrahedral silicate sheets and octahedral hydroxide sheets.

I know, that’s a lot of science words, so let’s break that down.

A tetrahedron is a shape that has 4 triangle faces, 6 straight edges and 4 vertex corners.

What ia a Tetrahedron | Clay Mineral Structures

A Silica Tetrahedron is 1 silicon atom bonded to 4 oxygen atoms.  A tetrahedral silicate sheet is made up of a bunch of the silica tetrahedron’s.

Quick note: Silicon has many benefits to your body and used both topically for skin healing and internally for weak bones, heart disease, hair loss, improving hair and nail quality.  In fact, I take biosil internally daily with my tea as a natural collagen generator.

What is a Silica Tetrahedron

An Octahedron ais a shape that has 8 triangle faces, 12 straight edges and 6 vertex corners.

What is a Octahedron | Clay Mineral Structures

An Octahedron is a shape that has 8 triangle faces, 12 straight edges and 6 vertex corners.

What is a Aluminum and Magnesium Octahedron

What is a 1:1 Clay?

When you put a bunch of connecting tetrahedron’s together into a sheet and a bunch of connecting octahedron’s together in a sheet, that makes a 1:1 clay mineral.  An example of a 1:1 clay mineral is Kaolin clay.

1:1 Clay Mineral Layers

What is a 2:1 Clay?

A 2:1 clay is like a octahedron sandwich, with a silica tetrahedron sheet on either side.  A 2:1 clay structure is a illite (french green clay) or montmorillonite (bentonite) clay.

2:1 Clay Mineral Layers

What’s neat is information about clay’s was only discovered only a short period ago with the advancement of x-ray diffraction technology in the 1930’s.

What is a Swelling Clay?

One of the coolest abilities that clay has is that some clay can swell up to 18X it’s size when hydrated.  Water can intervene in between the loosely bound clay particles that causes the clay to swell.

Bentonite Clay swells up to 18x it's size

But not all clays have the ability to swell.  The Smectite group of clays have the greatest ability to swell.  Remember those?  Bentonite, Rhassoul and Fullers Earth are some of the Smectite clays, whereas Kaolinite, and Illite clays are non expansive.

This will resonate a lot more with you when you are mixing your clays.  Notice how Kaolin Clay and French Green Clay require a much smaller clay to water ratio than bentonite or rhassoul clay do.

Swelling Capability of Clay Minerals Groups

The ability of the clay to swell also plays a role in the next section we are going to cover, the cation exchange capacity.

Why is a clay mask negatively charged?

So now that you know how the clay minerals are structured and identified, let’s dig more into how they work.  And what gives them their super power to work wonders on our skin.

What happens when clay is mixed with water is called the cation exchange capacity. (CEC), more on that when you keep reading.  In simple terms, the clay bond is negatively charged, so that attracts positive charged cations, just like a magnet.

First, let’s break down a bit of vocabulary:

  • What is an Ion?  Ions are chemicals with a charge.
  • What is a cation (pronounced cat-ion)?  Cations are positive charged ions.
  • What is an anion? Anions are negative charged ions.  

What are Cations and Anions?

How does clay get a “net negative” charge?  Sometimes an Isomorphous Substitution happens to give some tetrahedrons or octahedrons in the sheets, resulting in a negative charge. Remember that’s those shape layers from above. 

This happens while the clay is developing in crystallization and will not change after development.

 Isomorphous Substitution is the swapping of ions for another ion with the same or different compounds, but retaining the same type of crystal structure. 

Examples that will cause a net negative charged clay:

  • Substitution of the silicon 4+ for aluminum 3+ in some of the tetrahedral sheet will result in a negative charged clay.
  • Substitution of the aluminum 3+ with magnesium 2+ in some of the octahedral sheets will result in a negative charge clay.

It doesn’t need to be a complete swap of all the silicon for the negative charge to occur, just some of them.

Clay Particle with Net Negative Charge

The clay particles works very similar to how magnets work.  Opposite charges attract while like charges repel.

How positive and negative attraction of magnets work

The negative charged face of the clay particle attracts minerals (cations) to the surface of the clay.  Those cations can be a ridiculous number of cations (positive minerals), including: 

  • Ca2+: calcium
  • Mg2+: magnesium
  • Na+: sodium
  • K+: potassium
  • Fe: Iron
  • Si: Silica
  • +75 trace minerals

Negative Charged Clay Surface Particle with Positive Cations on Surface

When we refer to the minerals being “attracted” to the surface of the clay particle, what is happening here is actually a process called adsorption.  No, not absorption that you probably are familiar with, but adsorption. There’s a difference!

What is the difference between Adsoprtion and Absorption

When we have referred to those minerals being attracted to the negatively charged surface of the clay, we are referring to the sorption process.  They are different, so it’s important to know the different definitions.

Absorption (verb) – The process by which one thing absorbs or is absorbed by another.  Synonyms: soaking up, sucking up, drawing up/in

Adsorption (noun) – The adhesion of atoms, ions or molecules to a surface.  Synonyms: sticking to


Adsorption VS Absorption | How Clay Works

How does clay react with water?

When you mix your powder clay with water, all those beneficial positively charged minerals are made into a wonderful mineral paste, ready to apply to your skin or hair.

Water is di-polar.  That means that water has a slight positive charge on one side and a slight negative charge on the other side.  I think my water molecule below looks like a mickey mouse 😀 

Di-polar Water Molecule | How Clay works on your skin

Why does this matter?

It matters a great deal!  If you were to slather some of the clay powder on your face as-is, the benefits you would experience would be minimal.  That’s because when clay comes into contact with water, it swells and water activates with the charged ions.

An collection of water molecules that are physically attracted to the ion because of its charge, forms a hydration sphere.  See how all those water molecules are now attracted to the positively charged ion.

What is a Hydration Sphere | How Clay works with Water

Hydration forms around both positive and negative ions because water has a positive and negative end.  Here you can see the water molecules forming a hydration sphere around a cation and an anion.

See how they attach differently based on polarity?  The (blue) slightly negative side attached to the cation and the (red) slightly positive side attaches to the anion. 

Hydration Sphere around a Cation and Anion

The water molecules attract to the cations that are “attached” to the negative charged surface of the clay, forming hydrospheres.   

How Hydrospheres form on Clay Particles

Those hydrospheres detach the ions from the clay surface creating a mineral rich paste, ready to be applied in all it’s natural goodness to your skin. 

Clay Mask Science | Mineral Rich Clay Paste
There are 2 ways that clay detoxifies your skin, using adsorption and a cation exchange capability. 

How does clay adsorb impurities from your skin? 

Clay adsorbs impurities from your skin when oppositely charged ions attract to each other like magnets.  When they are adsorbs, they are sticking together.  When the clay dries and it’s removed from your skin then the toxin is dragged off the skin at the same time.  
Below we can see 2 negatively charged hydration spheres are adsorbed to a heavy metal (lead). 

Adsorption of positive ion by negative charged hydration spheres

What is a Cation Exchange?

Cation Exchange is an exchange of the cations.  This is actually pretty cool.

Cations are those positive charged happy faced ions.  Just because they are positive charged, that doesn’t mean that they are good minerals.

Basically, when mixed with water, the clay that has all those minerals attached to it’s negative charged surface, swaps those ions with equal or like charge.  AKA, good clay minerals are swapped for bad toxins and those toxins are removed from your face as part of the clay.

Being that clay is made largely of minerals, it’s leaving some of mother nature’s natural minerals behind on your skin.

Positive charged clay minerals swaps with positive charged toxins. This is called a Cation Exchange.  An example of this is with a positive lead ion swaps with a positive charged clay hydrosphere. 

Cation Exchange | How Clay can Detoxify your Skin

What is a Anion Exchange?

An Anion Exchange is the same principle as the Cation Exchange, except for it’s with negative charged ions.

An example of this is with a negative chlorine ion swaps with a negative charged clay hydrosphere.

Anion Exchange | How clay removes negative charged ions like Chlorine from your skin

What is a Cation Exchange Capacity?

Cation Exchange Capacity (CEC) a measure of the ability of the negatively charged clay to attract “cations”.  The cations a clay can hold, or the total negative charge, is the cation exchange capacity.

The cation exchange capacity is measured in milliequivalents per 100 grams of clay (meq/100g).  Here’s a comparison of the difference between each type of clay and the “strength” of the CEC ability:

Cations Exchange Capacity of Clay Mineral Type

Kaolinite: 10-20 m2/g CEC 3-10 meq/100g    |   Illite: 80-100 m2/g  CEC 20-30 meq/100g   |   Montmorillonite:  800 m2/g  CEC 80-120 meq/100g   |   Chlorite:  80 m2/g  CEC 20-30 meq/100g

As you can see above, the montmorillonite clay has a much larger surface area than the rest of the clays due to it’s swelling abiilty.  It also has a stronger ability to attract and hold cations to it’s negatively charged surface.

Ok, let’s recap all this information together.

  1. Clay is less than >2 micrometers in size.
  2. There are 4 types of clay mineral groups: kaolonite, smectite, illite, and chlorite.
  3. The clay’s are classified by their 2:1 or 1:1 sheets of tetrahedral silicate sheets and octahedral sheets.
  4. Tetrehedral silicate sheets are made of 4-sided triangle tetrahedrons made up of 1 silicon atom and 4 oxygens.
  5. Octahedral sheets are made of 8-faced triangle octahedral, with either magnesium and/or aluminum atoms and 6 oxygen atoms.
  6. There are non-swelling clays and swelling clays.
  7. Montmorillonite (bentonite) clay can swell up to 18x it’s size.
  8. Cation = positive ions.  Anion = negative ions.
  9. During crystallization of the clay, it goes through an Isomorphous Substitution which gives the clay a net negative charge.
  10. Net negative charge clays attracts positive charged minerals like a magnet to it’s surface.
  11. Some clays have insane swelling capabilities.
  12. Water is di-polar, so water mocules create hydration spheres around the positive charged minerals attached to the surface of the clay, creating a mineral rich paste.  Your clay mask!
  13. When mixed with water clay can adsorb or absorb impurities from your skin.
  14. Clay removes impurities by 2 ways, by adsorbing or by a cation exchange.
  15. A cation exchange is the swapping of positive charged clay minerals for positive charged toxins which are then removed from your skin with the clay.
  16. An anion exchange is the swapping of negative charged clay minerals for negative charged toxins which are then removed from your skin with the clay.
  17. Cation Exchange Capability is the ability of the clay to attract and hold cations to it’s negative charged surface.

Whew, that’s it.  Clay has also anti bacterial capabilities to cleanse as well as detoxify but I think we will leave that for another blog post.

This is a simplified overview of how clay works so we can understand the science behind how do clay masks work on our skin.  So now that you know how it works, check out our featured clay recipes below to experience the benefits of this pretty cool clay.

If you have any questions or comments, would love to hear your feedback and hope you enjoyed learning about the science of clay just as much as I did.

FAQ about How Clay Works

What are the different types of clay?

There are over 30 different types of clay, not all types are used for cosmetic purposes.

What are the 4 clay mineral groups?

The 4 types of clay mineral groups are Kaolinite, Smectite, Chlorite, and Illite.

What is a swelling clay?

A swelling clay, like bentonite, can expand up to 18 times it’s size!

What is the difference between absorption and adsorption?

Absorption is when one thing is soaked up by another. Adsorption is the adhesion of ions to it’s surface, i.e. sticking to it.

How does clay adsorb impurities from your skin?

Clay adsorbs impurities from your skin when oppositely charged ions attract to each other like magnets. When they adsorb, they are sticking together. When the clay dries and is removed from your skin, then the impurity is dragged off the skin at the same time.

Disclaimer, I’m not a scientist, this is my interpretation of how clay works with an ongoing pursuit of reading hours of research, studies and materials about how clay works.

Featured Clay Recipes:


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