Making Creams II: Theory – Formulas (O/W)

[Qui trovate la versione italiana di questo articolo]

These articles summarise what I believe to be the basics that one should know before making cosmetics at home. I do my best to link as many references and sources as possible to confirm what I’m writing, but you should never take anything as an absolute truth. Always check facts and information on more than one reliable source, and take these articles as starting point: keep studying and gathering chemistry knowledge before you actually start making cosmetics. If you notice errors, misleading information or you think I should cover further aspects of this theme, feel free to contact me!

In the previous article we learned the concept of emulsions and that cosmetic creams are emulsions.

[…] a cosmetic cream (and a cream in general) is an emulsion, which is a colloidal system in which inner droplet of a liquid are dispersed in an outer phase made of another liquid, with the two liquids being immiscible. The whole system is stabilised by the presence of an emulsifier.

Specifically, in a cosmetic cream we can have oil droplets dispersed in water (o/w creams) or water droplets dispersed in oil (w/o creams).

The stability of a cream depends on several factors, that are not limited to the presence of the right emulsifier: the viscosity of the outer phase, modulated by the presence of thickening agents, has an important impact on the stability of the dispersed droplets; at the same time, the size of the dispersed droplets is very important, and the smaller the droplets, the more stable the emulsion.

Now, let’s focus a bit more on the actual components of the cream. We understood that the minimum requirements are: water – oil – emulsifier. The previous article also suggested that the presence of a thickening agent is also good.

Let’s see the details of each phase that forms a cream. We will now focus on o/w creams, where the external phase is water and the inner phase is oil.

Outer phase: Water

The external phase is also known as continuous phase. In a o/w cream, it contains mainly water.

Water. In cosmetics, we don’t us tap water to make creams. Labs use distilled water. Hobbyists use deionised water, the one that supermarkets sell for ironing. Tap water is not used in the production of cosmetics because it contains a variable amount of ions, that we cannot know with certainty and that could have an influence on the stability of certain components of the formula (1). Beware: deionised water is not sterile. Some experts suggest to boil this water and let it cool down before using it, in order to kill some bacteria. However, you also have to consider that your homemade cosmetic product is not sterile at all, so it’s a bit like sterilising a needle and then spit on it before using it. If you feel safer, boil the water. Otherwise, just don’t use deionised water that you bought back in 1999.

Thickening agents. We mentioned them in the previous article, now it’s time to see who are they. Thickening agents are molecules that can increase the viscosity of a solution (2). We find them both in food and cosmetic industry. The ones we use in cosmetics are typically:

  • Polysaccharides, that is, polymers made of sugar units. Examples are Xanthan gum, Guar gum, Starch, Alginates, and Hydroxyethylcellulose.
  • Synthetic polymers, specifically, polyacrylates available with different commercial names, like Carbomer and Carbopol, but also Tinovis, Pemulen and Aristoflex.
  • Inorganic thickeners, like silica and modified clays.

The most commonly used thickeners in creams are polysaccharides and acrylates. What happens when we add them to water is that they start to swell, and this typically happens within a given pH range, and they convert the water phase to a gel-phase. Therefore, the water phase will be thick and this will have an influence on the final thickness of the cream, clearly, but also on the stability of the emulsion: the oil droplets will have a lower degree of freedom and it will be tougher for them to coalesce and separate from the outer phase.

Glycerin. Another components that we find in 99,9% of formulas is glycerin (or glycerol). Glycerin is an alcohol and we find it as a viscous and hygroscopic liquid. It is used in cosmetics as humectant, as it prevents the loss of moisture from the product (3). It is typically added to the water phase and in our DIY home lab we use it to help the suspension of some thickeners, like guar gum and xanthan gum, before adding the rest of the water.

Inner phase: Oil

In a o/w phase, the inner phase is composed by oil. The oil component of a cream is the one that will give the nourishing and emollient feel on the skin, and different oils can also have specific properties that are suitable for different kinds of skins. Here, we will only discuss plant-derived oils, but keep in mind that there are plenty of synthetic oils or natural and synthetic esters that are used in the cosmetic industry.

A part from the specific properties of each different oil, it is important to consider that each oil (or butter) has its own influence on the final feel and spreadability of the cream. Some oils are fatter and heavier than others, and the same goes for butters.

In addition, butters have different texture, with some being harder and some being softer, which translates in a different consistency at room temperature. This has an influence on the final thickness, consistency and feel of the cream.

There are a lot of studies and perspectives on how to choose the emollient combination of a cream. The aspects that one could take into account to finely tune the final performance of a cream are countless and I will not discuss them all.

As beginners, we could start taking into account the following aspects:

The overall fat percentage of the cream. This has to be planned when we decide if the cream is for a dry, normal or oily skin. Honestly, I haven’t found a clear and universal guideline percentage for the amount of oils that should be in a cream for different types of skin, because apparently each part of the world has its own preferences in this regards. In Italy, people say that the fat percentage should range from 10% for oily skin to 25% for dry skin in body creams, from 5% to 15% in face creams. In UK, they say from 3% to 20% (4). In Germany, they like oil phases and they get up to 35% of oils. Anyway, the thing is: how much oil you need in your cream depends on your type of skin (dry, normal or oily).

The spreadability and the skin feel of the cream. This is quite a complicated matter. The oil phase has a huge impact on how the final product will spread on your skin and how you will feel your skin after applying the cream. Will it absorb immediately? Will you still feel your skin nourished after a while? Will it feel greasy? This depends on the oils you use and on their balance. The spreadability and the more or less “heavy” feeling after the application depends mainly on two intrinsic characteristics of the oils: the viscosity and the surface tension (5). For most vegetable oils that we use, the surface tension doesn’t change all too much (6), therefore in this very basic discussion we will only consider the viscosity. Please note that viscosity is not equal to density. In many cases, a higher density is also correlated to a high viscosity, but it’s not always the case and they’re not correlated. The viscosity is a very nasty parameter to be measured and there are no comprehensive tables of viscosities for the vegetable oils we use in our self made cosmetics, therefore one should compare different data taken in different experiments and check that all the parameters were the same (it’s never like that, trust me).

Anyway, by checking a lot of papers and data sheets (7, 8, 9, 10, 11, 12), I got a rough idea of which oils are more viscous and which ones are less viscous. From the most to the least viscous:

  • Vitamin E (Tocopherol)
  • Castor Oil
  • Peanut Oil
  • Rapeseed Oil
  • Olive Oil
  • Sunflower Oil
  • Coconut Oil
  • Grape Seed Oil
  • Jojoba Oil
  • Dicaprylyl Ether

That’s why tocopherol and castor oil are perceived as heavy oils, while jojoba oil and dicaprylyl ether (or dicaprylyl carbonate) are perceived as light oils.

And that’s also why we typically use only tocopherol and castor oil in lipsticks and lip balms: because they must create an occlusive barrier on our lips and they should not migrate or disappear immediately.

A higher viscosity translates into a lower spreadability and a slower absorption feel, whereas a lower viscosity is related to a high spreadability and quick absorption.

So that’s the key to modulate the feel of our cream: balancing highly spreadable oils with low spreadable oils.

Even if you want to formulate a cream with a super quick absorption and light touch, you should include at least some “medium” spreadability oils, such that your cream does not leave a greasy feeling before disappearing.

Butters and waxes can have an influence on the skin feel, too: some butters, like cocoa butter, have a harder texture and a relatively heavy but still dry (not greasy) feel, whereas shea butter has a softer texture and nourishing feel.

The thickness of the cream. The choice and balance of the oils will have an impact also on the thickness of the cream (13, 14). This is influenced not only by the cascade of emollients that we planned to modify the spreadability, but also on the presence of consistency ingredients, that typically are esters or waxes (cetyl palmitate, cetyl alcohol, stearic acid, beeswax). Butters like cocoa and shea butter will also make the cream thicker. Thus, if you want to formulate a fluid lotion and not a super thick cream that feels like a butter, you should be careful in using too much consistency ingredients or butters (but you can add some, don’t worry).

The Emulsifier

Finally we reached the core of our cream, the moderator who makes everything stick together: the emulsifier.

As already discussed in the previous article, emulsifiers are molecules that can interact with both water and oil phase. They will distribute at the interface between the oil drops and the outer water phase, with their hydrophobic tails oriented towards the oil drops and the hydrophylic heads towards the water phase, and they will finally bring peace between these two worlds.

The most stable situation is when the emulsifier can interact well with both environment, but to reach it, we often have to couple more than one emulsifier. The typical case is a hydrophylic emulsifier and a more hydrophobic one. There are also products that you can buy as self-emulsifiers that already contain a pair of emulsifiers and you won’t need to add anything, maybe just a consistency ingredient.

Some emulsifiers:

  • Methyl Glucose Sesquistearate (Emulsan II)
  • Glyceryl Stearate-PEG stearate
  • Ceteareth-25
  • Cetearyl Glucoside
  • Polyglyceryl-3 Methylglucose Distearate
  • Cetearyl Olivate, Sorbitan Olivate (Olivem 1000)
  • Beta-Glucan (and) Pectin (Bergamuls ET 1)
  • Glyceryl Citrate, Linoleate, Oleate (Imiwitor 375)
  • Cetearyl Alkohol and Cetearyl Glucoside (Montanov 68)
  • Hydrogenated Lecithin (Phospholipon 80H)
  • Sucrose Stearate

And the list could go on and on!

All these emulsifiers are meant to work well in making creams: all you have to do is reading their data sheet and guidelines given by the producer and use them at the right percentage. Keep in mind that some of them need a consistency agent in the formula in order to further stabilise the emulsion and make the cream thicker.

Consistency agents

  • Cetyl Alcohol
  • Cetyl Palmitate
  • Stearic Acid
  • Glyceryl Stearate
  • Cetylstearyl Alcohol

And many more.

The emulsifier + consistency ingredients are typically mixed to the oil phase and melted with it; in some cases, the emulsifiers must be mixed to the water phase and heated with it. There are also emulsifiers that work at room temperature.

When you work with an emulsifier that must be melted (either in the water or in the oil phase), you should heat up also the other phase and bring them to the same temperature to ensure a successful emulsification process.

Focus on cationic emulsifiers: hair masks

Hair masks like the one you can find in this blog are creams, too. But in this case, they are “held” together by another kind of emulsifiers: the cationic emulsifiers. Cationic emulsifiers are very common in hair masks and hair products in general, because they interact very well with our hair surface and are perceived as conditioning agents. On the other hand, they are also emulsifying agents, therefore they can hold a cream together.

There are many cationic emulsifiers available and unfortunately, only few of them are also good for the environment (that means, not toxic for aquatic species).

The cationic emulsifiers I use the most are:

  • A blend known as Esterquat, that consists of Distearoylethyl Hydroxyethylmonium Methosulfate and Cetearyl Alcohol
  • Behentrimonium methosulfate

These two are claimed to have lower impact on aquatic life by Italian websites, compared to other known conditioning agents like behentrimonium chloride. However, I noticed that the available data report aquatic toxicity anyway (15, 16), therefore I would say that as long as you follow the percentage guidelines to avoid skin and eye irritation, it doesn’t matter if you use behentrimonium methosulfate or behentrimonium chloride.

Preservatives

I know that there are people and even companies claiming that their cosmetics are preservative-free, paraben-free, and so on.

I hope it’s not true, because a cream without preservatives is a cream that will soon become home to a community of bacteria, mold and fungi.

Preservatives are not super cool if you would use them pure and directly on the skin, that’s true. But they don’t have to be used like that! You just have to add them to your cream in a tiny percentage (use percentage of preservatives is typically around 1%) and it will be sufficient to preserve your cream from contaminations during its lifetime.

There are many broad-spectrum preservatives that you can use. Some examples:

  • Parabens. I start with the most hated type of preservatives. A long time ago, a study speculated that they could cause cancer. The study was then disputed, but the public opinion on parabens was affected forever. There are no real evidences of their effect on human health (17), so just don’t panic if you see them in a cosmetic product. They are allowed also in the European Regulation (18). Parabens are effective against gram positive bacterial and fungal infections, and they must be combined with a gram-negative active preservative (19). Some parabens are:
    • Metylparaben
    • Butylparaben
    • Propylparaben
    • Germaben II: mixture of Propylene Glycol, Diazolidinyl Urea, Methylparaben, Propylparaben
  • Formaldehyde releasers. These molecules release small amounts of formaldehyde and they are combined with other preservatives (such as parabens) to provide a broad-spectrum protection against contaminations (20). Their use in cosmetics is restricted to certain limit concentrations in EU. The most common are:
    • Imidazolidinyl Urea
    • DMDM Hydantoin
    • Diazolidinyl Urea
    • Quaternium-15
  • Phenoxyethanol. This compound is widely used as preservative, as it has a broad spectrum activity and can be employed in a wide range of pH. It is often combined with other preservatives.
  • Benzoic acid, Sorbic acid, Levulinic acid (and relative salts: sodium benzoate, potassium sorbate). They are the most common natural preservatives – although they’re still chemical compounds like the others and they’re not produced naturally. They are typically combined with other preservatives.
  • Benzyl alcohol/Dehydroacetic acid (known as Geogard, Cosgard, and other names). One of the most popular preservatives in DIY-cosmetics, it has good antibacterial and antifungal activity but it’s a bit weaker against mold (21). It can be combined for example with potassium sorbate to enhance protection against mold.

Preservatives are often heat-sensitive, therefore they are added to the cream only once the emulsion has been established and cooled down. They are part of the so-called cooling down phase.

Functional ingredients: the fancy part of the cream

So far, we have seen the minimal components of a cream:

  • Water (+ thickening agents)
  • Oil(s)
  • Preservative(s)

But there is much more than this that we can add to our cream: it’s time to talk about functional ingredients.

Functional ingredients are all those molecules that have a specific (good) property for our skin or our hair, like

  • Moisturizers
  • Anti-aging
  • Conditioning
  • Equilibrating
  • Purifying
  • Providing sun protection

And there are many more. Some are actually just marketing ingredients, like most of the functional ingredients claimed in shampoos and rinse-off hair products. Some are really useful. I will give some examples of the functional ingredients I prefer for my skin type. I tend to have very dry skin, therefore I typically use moisturizers.

Panthenol. It is a pro-vitamin of the B-complex group and a normal constituent of skin and hair. It is employed in dermatology in the preservation of skin health, even in some preparations for wound-healing (22). I use it for its moisturizing activity only in skin products: while it’s true that it is a component of hair, it won’t be absorbed by the dead mass of stuff that is our hair. Maybe it can create a coating around the hair, like most moisturizers and humectants do, but it won’t repair or nourish the hair (23, 24). You can use it as 75% solution (it is very dense) in the cooling down phase at concentrations between 0.5 and 5% (25, 26). Keep in mind that this product has a basic pH (8-9).

Sodium Lactate. Sodium lactate is the sodium salt of lactic acid. It is used in cosmetics as buffering agent as well as moisturizer, as it is also natural constituent of the skin natural moisturizing factor (27, 28). It is useful also as buffering agent, meaning that it helps keeping the pH stability of a product – especially when there are elements in the formulation that can increase it or decrease it over time, like urea. You can use it as 60% solution at maximum concentration 10% (29).

Hyaluronic acid/sodium hyaluronate. Hyaluronic acid is one of the VIPs in the moisturizers community, mainly because of the claims about its anti-aging effects, which I totally ignore. Whether it is anti-aging or not, it is a good moisturizer. Nowadays there are also a lot of claims and confusion about the molecular weight you should use, with companies claiming that the lower molecular weight would penetrate the skin and the higher not. I have a lot of concerns about the penetration of functional ingredients through the skin via the simple topical application of a cream, but if you want to know more, just look for some papers. I use the medium-high molecular weight sodium hyaluronate by Glamour Cosmetics simply as moisturizing/humectant agent in creams and gels. You can either use it like it is (at 0.2-0.5%) or make a gel out of it with 1% concentration and use it as functional ingredient in your cream (1-5%).

To make the 1% sodium hyaluronate gel: prepare 99 g of deionised water that includes a preservative at its recommended percentage. Add sodium hyaluronate powder by distributing it on the water surface. Let sit overnight: sodium hyaluronate will hydrate and swell, forming a gel.

Sodium PCA (sodium salt of pyroglutamic acid). This is another moisturizer. It’s the only functional ingredient that I like to use also in leave-in hair products, because of its anti-static effect. You can use it in the cooling down phase or directly in the water phase (it’s not heat-sensitive) at 1-10% concentration (I typically use it at 1%) (30).

Allantoin & Urea. Allantoin and Urea are moisturizers that can have keratolitic effects at high concentrations. Allantoin is not very soluble in water and it is typically employed at 0.4% in the water phase (the typical concentration range is 0.1-0.5% (31)). Urea can be found in cosmetics up to very high concentrations in keratolitic products; as moisturizer it can be used around 2-5% for example.

Important: stabilization of urea in cosmetic products. Urea can undergo decomposition into carbon dioxide and ammonia, if not stabilised, leading to a pH increase of the product over time (32, 33). Urea should not be exposed to high temperatures and should be stabilised in the product with the presence of buffering agents, for example a lactic acid/sodium lactate buffer or with stabilisers like triethyl citrate. The pH of the product should be not higher than 6.

Alpha-Bisabolol. Alpha-bisabolol is a sesquiterpene component originally derived from Chamomile. It is employed in cosmetics for its anti-inflammatory and protective effect on skin. However, its use should be limited to a 0.05-0.2% of the formulation (34). It is soluble in alcool and oils, not in water.

Niacinamide. Niacinamide, or nicotinamide or vitamin B3, is employed in cosmetics as functional ingredient, since it can help improving the barrier functionality of the skin and can provide several benefits in its appearance (35). It is typically used within a pH range of 5-6 to avoid possible hydrolysis into nicotinic acid and ammonia. The employed concentration can vary, I use it at 1-2%.

Inulin. Inulin is a polysaccharide that can be used as skin and hair conditioning agent and humectant (36, 37). I use it at 1-2% dissolved in the water phase (it is not heat-sensitive).

Cosmetic fragrances

One of the first things we do when we hold a new cosmetic products with our hands is smelling it. In fact, the nice scent of a cosmetic product is an important part of the cosmetic experience, therefore we should take it into account also when we make them on our own.

Among the basic reagents and functional ingredients, in most supplier shops we find cosmetic fragrances and essential oils. These can be used to give our cosmetic a specific scent, whether we want it to smell like Jasmine or Roses or… Cotton Sugar.

Perfume experts can also combine different cosmetic fragrances and create wonderful scent combinations, but I’m not one of them.

In this article, I will only tell you the ugly part of cosmetic fragrances: there’s a limit in how much fragrance you can put in your cosmetics. This dosage limit is typically stated in the data sheet of the specific cosmetic fragrance you buy. Moreover, you have to consider possible allergies and sensitizations to specific components of the fragrances.

When using cosmetic fragrances, I typically add up to 1% in body creams and 0.5% (or none) in face creams – because scented products on my face bother me a lot.

With essential oils, you must be even more careful: just because they’re natural it doesn’t mean they’re safe and you can add an entire bottle to your cream. Always follow the guidelines on the data sheet and take a look also here and here. And remember that some essential oils are photosensitizing – bad reactions upon sun exposure after application can occur!

The pH

pH is a very important parameter of a cosmetic products. Long story short: our skin has its own surface balance and pH, which is on average around 5 (38, 39). Although skin has buffering abilities, that help restoring the balance if it comes in contact with aqueous acid or basic solutions (40), we don’t really want to apply something on our skin that is completely off the range of pH that it likes. That’s why our creams should have a final pH that is also around 5 (typically it can range between 5 and 6). This is true also for the hair scalp. Hair products typically have even lower pH (between 4 and 5) because higher pH level tend to increase the negative charge and subsequently the friction between the hair fibers, possibly leading to fiber damage (41) – which is one of the reasons why solid shampoos are not soaps.

Therefore, at the very end of your production, you should always check the pH of your cream (if you want to be super precise, you should have a pHmeter, but most hobbyists use pH stripes) and adjust it to the desired value.

But what does pH mean? pH is a scale used to measure how acidic or alkaline an aqueous solution is. It is a logarithmic scale that is inversely proportional to the hydrogen ions concentration in the solution, which are related to the dissociation of acids. Specifically, pH = -log[H+] where [H+] is the hydrogen ions concentration. For example, the [H+] of 0.1 M HCl, pure water and 0.1 M NaOH are 10^-1, 10^-7 and 10^-13, respectively. That means that their pH values are 1, 7 and 13, respectively. A solution with pH = 7 is considered to be neutral; below this value, the solution is acidic; above this value, the solution is alkaline.

To lower the pH of a solution (or of a cream, in our case), you will need an acid. When we make creams at home, we typically use a citric acid or a lactic acid solution.

To increase the pH of a solution (or of a cream, in our case), you will need a base. When we make creams at home, we typically use a sodium hydroxide solution. Not sodium bicarbonate nor sodium carbonate!

So, how does the formula look like?

With all this being said, we can summarize the whole article with the following table, that shows how a cream formula will look like.

A: Water (outer phase)Function%
Deionised/distilled waterSolvent 100-%of all the other components
GlycerinHumectant1-10%
Xanthan Gum, Guar Gum, Polyacrylates…Thickening AgentRecommended dose for the specific thickening agent (typically 0.1-1%)
(opt.) Sodium Lactate, Inulin, Allantoin…Heat-stable functional ingredientsRecommended dose for each functional ingredient
B: Oil (inner phase)Function%
Methylglucose sesquistearate, Ceteareth-25, Olivem1000, Phospholipon 80H… Main emulsifying agentRecommended dose for the specific emulsifier
Cetyl alcohol, cetyl palmitate, stearic acid…Consistency factor0.5-3
Beeswax, Bellina wax…Waxes0-1
Cocoa butter, shea butter, mango butter…Butters0.5-7
Oils (high viscosity – medium viscosity – low viscosity according to desired spreadability and after-feel)Oils5-25
C: Preservatives + Functional ingredients + ExtrasFunction%
Benzyl alcohol/dehydroacetic acid, potassium sorbate, phenoxyethanol…Antimicrobial, antifungine, against moldRecommended dose (typically between 0.5-1)
Panthenol, Sodium hyaluronate…Functional ingredientsRecommended dose
Cosmetic fragrancePerfume0-1
Citric acid solution or NaOH solutionpH-balancing reagentsAs needed to reach the recommended pH
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