Two aspects which affect the harshness or mildness of cleansers: Micelle size and pH


I originally wrote this for Sokoglam’s Klog, however, I think it’s still worth sharing and hopefully you find it informative and interesting!


Cleansers are one of the few times in skin care when we actually remove things from our
skin, and a good cleanser will remove things that we don’t want on our skin, while minimizing the removal of things we do want in our skin. Removing soil, makeup, sunscreens, sebum, and pathogenic microbes are beneficial to the health of our skin, but the chemicals we use to dissolve and remove those unwanted substances can also remove components from our skin that provide it protection and moisture.

How do cleansers work?

Cleansers work by dissolving and emulsifying things off of the skin that aren’t normally rinsed away by water. Water on its own can rinse away some soils, but it has a harder time rinsing away lipids – like the oils and waxes produced by our skin and added to the skin from products.

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Modern cleansers employ surfactants, named because they are active on the surface (surface active agent) of where two things meet – in this case water and lipids. One end of the surfactant molecule dissolves into lipids more readily, and the other end dissolves into water more readily. When surfactants come into contact with lipids and embedded soils on the skin they lift it off the skin’s surface and because the surfactant can still partially dissolve in water, the whole mixture can be rinsed off with water.

Two aspects that contribute to a cleansers gentleness or harshness

Micelles

When we pour a tiny amount of surfactants into water, they’ll all sit on the surface of the water in a film, with their lipid dissolving ends sticking up into the air.

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Hydrophobic means water-fearing, these are the lipid dissolving ends of the surfactant molecule. Hydrophilic means water-loving, these are the water dissolving ends.

Once there’s no more room on the surface, additional surfactants are pushed down into the water. Here they can begin to form bubble-like structures called micelles.

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Now what, exactly, is a micelle? A micelle is a sphere, with the surfactants’ lipid dissolving ends pointed towards the center. This keeps them as far away from the water as possible. (Heard of micellar water? That’s a dilute solution of water with surfactant micelles in them)

The formation of micelles isn’t permanent though. These spheres are constantly rearranging and reforming, breaking into individual surfactant molecules and rejoining other micelles.

Surfactant molecules can also organize in ways other than spheres, such as the lipid bilayer seen in our skin.

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Individual surfactant molecules are harsher to the skin than grouped surfactants in a micelle. The individual surfactant molecules’ smaller size allows them to penetrate past the outer layers of the skin and work their way in-between our skin lipids, which help retain moisture of the skin. Surfactants can also bind to proteins, enzymes, and cell membranes. This warps their structures, which can lead to inflammation. We see this inflammation as redness, and eventually scaling and drying of the skin.

Some individual surfactant molecules are so small, like sodium lauryl sulfate, that even their micelles are small enough to penetrate past the outer layers of skin. Sodium lauryl sulfate, on its own, is so good at causing irritation that it’s often used as an irritation control in skin studies.

By reducing the amount of free individual surfactants in a cleanser and by increasing the size of a micelle, we can make a gentler cleanser! This can even be done with a harsh surfactant, like sodium lauryl sulfate. Just because it’s on an ingredient list, doesn’t necessarily mean the cleanser is going to be harsh.

One way mixing surfactants can increase the micelle size is by being different sizes. The size difference of the different surfactants disorganizes the sphere shape of the micelle and increases the surface area, which creates a gentler cleanser.

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There are other ways to increase the size of micelles and reduce free individual surfactants too. The most common way is to add proteins and polymers into the cleanser. These not only join in on the micelles’ structure – enlarging them, they can also bind free surfactants, so they’re less likely to bind to your skin’s components.

pH

The pH of a cleanser can have an impact on the harshness of a cleanser as well, but most often in an indirect way – especially with modern surfactants.

Our skin’s surface has acidic components on it that create a slightly acidic environment which keeps certain bacteria at bay. Each deeper layer of skin increases in pH, eventually reaching a less acidic pH closer to 7. This pH gradient has important functions, such as controlling the activity of enzymes in different layers of the skin.

Cleansers affect the skin in two ways, and the first is a chemical interaction. Acidic and alkaline chemicals interact and form new compounds which can alter the pH of the skin.

The second way skin’s pH is affected by a cleanser is simply by the removal of acidic components, like free fatty acids and others, from the skin. This is why almost any cleanser, including water, can temporarily raise the pH of the skin.

Healthy skin can replenish its pH to normal levels on its own, often in less than an hour. One of the ways skin maintains its acidic surface is through the activity of enzymes that are constantly breaking down lipids and other components of the skin and turning them into acids.

Using an acidic product after cleansing won’t restore the acidic components back to the skin, but it may help facilitate your skin’s process in creating new acidic components. In the same sense, adding alkaline substances to the skin may hinder the process.

When it comes to cleansers, this all just means that if we take two cleansers that are identical except for the pH, the acidic one is often (but not always) more gentle. pH adjusted cleansers often contain surfactant mixtures with larger micelles as well!

Putting it all together…

As a consumer it can be difficult to tell if a formulation is going to be gentle or not, especially based on the ingredients and a pH test. There are even more factors that determine the mildness of a cleanser and some of that is subjective.

If you’re looking at listed ingredients, decyl glucoside is considered a very mild surfactant. However, it removes almost as much lipid from the skin as sodium lauryl sulfate. It can be formulated to predominately remove lipids from the surface of the skin, which maintains its mildness, but it might also leave your skin feeling stripped, since there’s no lipids on the surface.

Some tips to identify gentle cleansers

Look for multiple surfactants! I personally look for surfactants like decyl glucoside, coco-glucoside, disodium cocoyl glutamate, disodium laureth sulfosuccinate, cocoyl methyl glucamide, sodium cocoyl isethionate, and lauryl lactyl lactate. Though the names can be hard to pronounce, they’re very mild to the skin on their own, reduce irritancy of harsher surfactants, and are bio-degradable.

Look for skin-moisturizing ingredients, like oils, butters, proteins, and amino acids.

Be cautious about high pH ingredients like sodium palmitate, sodium cocoate, and other saponified oils. These surfactants aren’t easily pH adjusted, as they form fatty acids in acidic solutions which are oily and less effective cleansers.

Keep in mind this list isn’t exhaustive!

How to use a cleanser gently

Use cool or cold water to clean your skin! This makes it less likely for lipids to be removed from within the skin. Hot water can also decrease the size of micelles and increase the amount of free surfactants, which leads to more irritation.

Use less cleanser! A cleanser doesn’t need to foam for it to work. The concentration of surfactants at which they start forming micelles is often very low. For example, for gentler surfactants like decyl glucoside it’s around 0.08%. Most cleansers contain between 15% to 60% surfactants.

Use something after! Even water will remove some lipids from the surface of the skin, so it’s helpful to put on a moisturizer. Those with oily skin might consider a watery serum or gel.

Those with very sensitive skin may consider using diluted cleansers, like micellar water or cleansing lotions. Using them with a cotton round assists in the removal of soil and grime. I’d still recommend rinsing your face after cleaning, though, because sometimes surfactants left on the skin can lead to irritation.

Can you use Niacinamide and Vitamin C (Ascorbic Acid) together?

Yes! (For most people.)

Niacinamide and ascorbic acid on their own are great skin care ingredients. Ascorbic acid is not only a good water-soluble antioxidant, but may also increase production of collagen in the skin which can help mitigate some of the damaging effects caused by UV exposure.

Niacinamide is a good anti-inflammatory which makes it useful for treating inflammatory conditions like acne and has been shown to increase naturally occurring moisturizers in the skin.

They’re both very effective at reducing hyperpigmentation of the skin – it’s easy to see why people would want to use the two of them together.

 

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If you Google Niacinamide and Vitamin C, you’ll get some posts about not combining them. The worry is that they form a 1:1 complex and cancel out each other’s skin benefits.

There are two main chemical reactions that occur when you mix niacinamide and ascorbic acid. The first occurs when you mix niacinamide with any acid (or base), and that’s the conversion of niacinamide to niacin. This takes a long time and is more of a concern for manufacturers that are using niacinamide in acidic products.

It’s possible that niacin is just as effective as niacinamide, but it has the side effect of activating Langerhan cells in the skin. This leads to the release of prostaglandins and dilation of the blood vessels, which causes the skin to flush with redness and tingle. This flushing and tingling is temporary, but can be uncomfortable and potentially problematic for someone with inflammatory acne or erythema.

The second concern is the formation of a complex between niacinamide and ascorbic acid. I think the worry is that this complex is no longer effective in benefiting the skin, and I’ve also seen concerns that it may produce hydrogen peroxide which can lead to skin cell death.

I took a look at the research to get a better understanding of these two chemical reactions. It is important to note that a few of these papers are old, so they don’t use newer visualization techniques that can help us quantify chemical changes and structures more accurately.

Hydrolysis of Niacinamide to Niacin

Amides, like niacinamide, are very stable compounds. This stability means it takes a lot of heat and concentrated acids or bases to get niacinamide to turn into niacin (also known as nicotinic acid).

I’m going to do a separate post that will explain this more, but the important thing to see is that the -NH2 group, a nitrogen and two hydrogens, is replaced with an -OH group, an oxygen and a hydrogen.

In fact, niacinamide is so stable, that a 10% solution can be heated to 120 °C (248 °F) for 20 minutes with no niacin forming.

In another experiment it took about 75 hours in a pH 2 solution at 90 °C (194 °F)  to convert about half the niacinamide to niacin.

Heat vastly speeds up reactions; a rough approximation is that every 10 °C (18 °F)   increase in temperature doubles the reaction rate. If the pH 2 solution was kept at 30 °C (86 °F)   we could expect it to take over 4800 hours or almost half a year – and that’s if the acidic solution didn’t corrode your skin first!

An experiment with temperature conditions closer to room temperature shows how heat affects the rate of conversion. Only after 6 weeks of storage at 45  °C (113 °F) in acidic pHs did they find niacin, and the conversion never exceeded 2%. At room temperature (25 °C or 77 °F) the amount of niacin was less than 1% after 6 weeks, but the measurement wasn’t accurate enough to tell exactly how much, just that a small amount was present.

Another thing to keep in mind is that reaction rates also slow down when the viscosity or thickness of the solution is increased. Most skin care products, even serums, are thickened to some extent – which will further slow down the conversion of niacinamide to niacin.

If we can get metaphorical for a second, chemical reactions aren’t like a distance race. They’re more like jumping over hurdles. There’s a minimum amount of energy that’s needed to cause the molecule to change, called the activation energy. If you don’t have the energy to jump over a hurdle, you can’t progress. You can’t just roll on the ground until you hit the finish line.

What all this means is that products formulated with niacinamide and an acid may produce some niacin over time. This can be a problem for some, as even a miniscule amount of niacin can produce some faint skin redness, as little as 0.001% – amounts in the range of 0.01% to 0.1% will produce much more apparent skin redness for more people.

It’s also important to note the difference between irritation due to an acidic product versus the flushing caused by niacin. Niacin flushing appears evenly, affecting everywhere it’s been applied. It is also temporary (often lasting longer than 20 minutes), and comes with a tingling sensation.

If you’re using a product with niacinamide and ascorbic acid in the ingredients list and aren’t noticing any skin reddening…there’s either very little niacin that’s been formed, or you’re not very sensitive. If you’re worried about a product that contains both ingredients, storing it in a cool environment will discourage transformation of niacinamide to niacin.

But what about applying a product with niacinamide and then one with ascorbic acid? Is niacin being formed? I don’t want to say absolutely not, but the amount potentially formed is so miniscule, I don’t think it’s a relevant worry.

Niacinamide and Vitamin C (Ascorbic Acid) Complex

Mixing niacinamide and ascorbic acid turns the two clear solutions a yellow colour, but this isn’t the same yellow colour that appears when ascorbic acid is oxidized into dehydroascorbic acid.

This yellow color is due to the formation of a charge-transfer complex, called niacinamide ascorbate. An electron is transferred from the ascorbic acid to the niacinamide – this weakly holds the two together.

I think the fear of this complex negating the benefits of both ascorbic acid and niacinamide is not knowing that this complex is easily reversed and separated.

An experiment found the association equilibrium, or the balance of free ascorbic acid and niacinamide to niacinamide ascorbate, to be 1.45 at 25 °C (77 °F) .

This experiment also found that the pH of the solution that the two are mixed together in affects how much of the niacinamide ascorbate is formed. Niacinamide ascorbate forms best at a pH close to 3.8, but at pHs higher or lower less is formed. This means if the pH of a solution they were mixed together in was changed, away from 3.8, the two molecules would separate from each other.

This means if we added the same number of molecules of niacinamide and ascorbic acid into a solution of pH 3.8, about half of them would be in the niacinamide ascorbate complex, and the rest of them would just be on their own floating around.

I’m going to do a separate post that will walk through the calculation of this.

The pH dependent formation is important, because only the surface of our skin is acidic. Each deeper layer of skin becomes less and less acidic, finally reaching physiological pH which is around 7. This means as the niacinamide ascorbate moves deeper into the skin, there’s less impetus for them to be associated with each other. As well, as more individual ascorbic acid and niacinamide molecules move into the skin, the ratio of free to complexed niacinamide and ascorbic acid would decrease, and the complexed niacinamide ascorbate would separate until equilibrium was reached again.

One study that used niacinamide ascorbate on human skin explants found that it was still able to reduce melanin production in response to UV exposure. So it would seem its active effects aren’t hampered by being complexed together.

Another experiment found that the niacinamide ascorbate complex helped stabilize the ascorbic acid against degradation.

So the important takeaway is to know that the yellow colour isn’t the same thing as an oxidation of ascorbic acid, and that the complex formed between niacinamide and ascorbic acid is completely reversible. The niacinamide and ascorbic acid are held together like two pieces of paper with static, versus glue.

There is one paper that is cited to say that UV exposure caused the production of hydrogen peroxide in the skin when niacinamide and ascorbic acid were used together, however the effect was small and the proposed peroxyl radical mechanism is theoretical.

Many skin care ingredients will degrade or change with UV exposure, but using a sunscreen will greatly reduce or even eliminate the chances of this occurring.

The paper also theorized that by mixing the niacinamide and ascorbic acid with tocopherol (Vitamin E), the radical production could be mitigated.

Takeaway

I hope this has helped you understand what’s occurring when you mix niacinamide and ascorbic acid (or any acid) together. While there are chemical reactions that occur, they either occur super slowly, or are reversible.

You can definitely still choose to use niacinamide and ascorbic acid separately. You could use ascorbic acid during the day and niacinamide in the evenings. If you do choose to use them together, I don’t think the evidence points to any disabling of their benefits or any skin damage.

People do often experience some redness or tingling when using the two, but I think that can be chalked up to the irritation caused by ascorbic acid, especially if the product isn’t pH adjusted and acidic. I don’t want to suggest you to take a niacin pill to experience a flush, but unless the redness is very even and demarcated, it’s not likely due
to niacin.

Edit: Nicotinic, not nicotonic – apologies for the typo!