Formulation philosophy and how to make substitutions

[Versione italiana]

If you have read all the articles of the chemistry course for DIY formulators, at this point you probably already started to make your first cosmetics or you are preparing to do so. 

I think this is the right moment to think about what is your formulation philosophy: if you have a clear idea of how your formulations should be like, in terms of type of ingredients and reasons behind them, it will be much easier for you to understand how to replace ingredients of someone else’s formula without breaking the formula apart. 

Establish your boundaries

What does it mean to have a formulation philosophy? It means that it should be clear to you what are the objectives you want to reach with your DIY cosmetics and what are the ideas behind them. 

First of all, ask yourself why do you want to make cosmetics on your own. There can be many different personal reasons, I can only tell you what I learned speaking with other people:

  • Some people want to replicate or even surpass the performance of commercial products; 
  • Other people do it just for fun, like any other hobby;
  • There are people who do it for environmental reasons;
  • and people who do it to save money while still having good cosmetic products

And these are just few of the reasons that push people to make their own cosmetics (often the reasons are more than one). You should first of all understand what is your reason and what is your purpose, because this determines the boundaries of your formulations and of your choice in terms of ingredients. 

People who want to simulate or improve the efficacy of commercial products might be more performance-oriented, and for them it might be indifferent whether the ingredient is natural, synthetic or naturally-derived. People who do it for environmental reasons might be more oriented towards “green” and eco-sustainable ingredients. 

My personal philosophy is that I would like to make cosmetics that work for me, but at the same time with ingredients that are as biocompatible (biodegradable) as possible; and I try to find ingredients that I can use in more than one type of cosmetics, in order to reduce the amount of ingredients and resources that I have to buy. 

Once you decided what are the boundaries of your ingredients choice, you should study the theory and the particular features of all your ingredients, because you should be able to answer the question: why did you put that ingredient in your formula? If you don’t know how to answer this question, the risk is that at some point you will use something useless in your formula (and waste your time and money) and/or something that does not really belong to your philosophy. 

If you know exactly the role of every single ingredient in your formula, you will get a lot of advantages:

  • You will not waste money by buying ingredients just because you saw them in a formula but without really knowing if you can use them or not
  • If something is weird in your final product when you test it out, you can have an idea of what you should change (is it the consistency factor? is it something in the spreadability? is it too fat? etc.)
  • You will be able to make substitutions.

Substitutions

So when you try to replicate someone else’s formula, it could happen that you don’t have all the same exact ingredients of the original formulator. But if you understand the role of each component of the formula, you should be able to make substitutions. 

Almost everything in a formula is replaceable, as long as you have an ingredient that does the same thing. 

Let’s see some categories of ingredients and how to replace them.


Water. Water is actually one of the almost irreplaceable ingredients. It is the solvent of most non-anhydrous preparations and you should always use deionised water. 

In some formulas you can find a hydrosol used as solvent instead of water: in this case, if you’re not interested in the particular properties of the hydrosol you can use simple deionised water. 


Rheology modifiers. Ingredients like carbopol, carbomer, xanthan gum, guar gum are interchangeable. They all do the same thing, that is, modifying the viscosity of water phases. They can have different performances in terms of flow, with some synthetic rheology modifiers being awesome for hydrogels (whereas xanthan gum is not the best option, but if you can accept it, it still does its job). 

Although they’re replaceable with each other, you should pay attention to some details:

  • Use level: when replacing a rheology modifier with another one, always check the use level of the one you want to use.
  • Incompatibility with other ingredients: if you are replacing for example xanthan gum with a synthetic rheology modifier, you should check that in your formula there is nothing that interacts badly with it. Same for the replacement of guar gum derivatives with xanthan gum or synthetic thickeners in hair conditioners that include cationic emulsifiers.

Glycerin. Together with water, glycerin is one of the almost-irreplaceable ingredients. Luckily for us, it’s pretty cheap and easy to find. Just buy it. 


Emulsifiers. Emulsifiers are, like rheology modifiers, basically interchangeable.

  • Always check the use level of the specific emulsifier you want to use
  • Check if you need a co-emulsifier or not
  • This should be obvious, but: check that the emulsifier you want to use is actually for the type of emulsion you want to make (O/W or W/O)
  • Consider that different emulsifiers can give different performance in the cream: some emulsifiers are a bit waxy, others are very light and thin. You should take this in consideration according to the needs of your emulsion. 

Consistency factors. 

  • Fatty alcohols like cetyl and cetearyl alcohol are interchangeable. Cetyl palmitate is also a good option. 
  • Waxes are interchangeable as long as they have similar melting point. This means that you could replace beeswax with bellina wax, but not beeswax with carnauba wax. The thickness of the cream would change dramatically. Check the Anhydrous products article for more detail information about waxes.

Emollients. If you read the Fat side of the cream and the anhydrous products articles, you should know how it works with emollients by now. 

  • Butters are interchangeable as long as they have similar melting points, like with waxes. Check the Anhydrous products article for more information.
  • Emollients are interchangeable as long as they have similar viscosities, if you want to maintain a similar spreadability to the original formula. If you are more interested in the composition of emollients in terms of fatty acids, then they are interchangeable as long as they have similar insaturation levels. If you are concerned about the comedogenicity of emollients, though, you should take into account the comedogenic rating, too. Check the Fat side of the cream article series for more information.

Functional ingredients. Functional ingredients are interchangeable as long as they do the same thing. In general, if you don’t have a specific functional ingredients it won’t be the end of the world: they don’t have a role in the stability of the cream, but only in their effect. And most of them are just claims, therefore there is a lot that you can just skip. If you are interested in hydrating substances, they are kind of interchangeable but they also work very well in synergy, therefore I suggest to buy some. Check the Hydrating substances article for more information. 


Preservatives. Preservatives are NOT an option. They must be there, period. 

Which preservative to use is your choice, as long as it is a broad spectrum preservative and compatible with the pH range of your product. Keep in mind that:

  • Products containing water must be preserved with a broad spectrum preservative. You can choose between many different types (benzyl alcohol/dehydroacetic acid + potassium sorbate, phenoxyethanol, parabens, sodium benzoate, levulinic acid salts, etc.) and they typically require a rather low use level (0,5-1%). Check the optimal pH range.
  • Anhydrous products that do not enter in contact with water don’t need such a preservative, but they might need an antioxidant like tocopherol (0,5-1%).
  • Anhydrous products that enter in contact with water (solid shampoos and solid conditioners) need a broad spectrum preservative just like any other water-based product.
  • Soaps don’t need an antimicrobial preservative, but it’s good practice to use antioxidants (rosemary oleoresin) and chelating agents (sodium gluconate) to protect against rancidity processes.

Fragrances and essential oils. Of course you can change the fragrance or the essential oil of a formula. If you seek for a specific functional activity of an essential oil, maybe you should consider that, but if it’s just about the perfume you can use whatever you want. 

There are mainly three aspects you should be careful about about replacing fragrances/essential oils:

  • Photosensitization: some essential oils (like those of the citrus family) are photosensitizing. You should be careful if you plan to use them in a skincare product.
  • Maximum use level: some essential oils are very strong and can be very irritating. Always check the use level of specific fragrances and essential oils. 
  • Use in lipcare products: in lipcare products you should only use flavours and essential oils that are specifically allowed for the use in lipcare products. Only few essential oils are. 

Pigments. In mineral makeup, you can of course choose the colour you want. But pigments are not food dyes: always use inorganic pigments or vegetable-derived pigments that are meant to be used in mineral make up. Food dyes, crayola markers, pencils, those are NOT to be used in mineral make up. In addition, always check that pigments are suitable for lipcare products, if you want to use them in lipsticks (some are not). 


Citric acid as pH regulator. Citric acid 30% solution can be replaced with lactic acid 30% solution. 

Sodium hydroxide as pH regulator. Some DIYers use sodium carbonate instead of sodium hydroxide 30%. Actually you should use sodium hydroxide: it’s a strong base, only few drops are sufficient to change pH and there’s no risk to develop unwanted bubbles in your preparation. 


Sodium hydroxide as soap reagent. No, you cannot replace it. Soaps must be made with a strong base, and in most cases this strong base is sodium hydroxide (lye). The only alternative to it is another equally strong base, that is “potash lye” (potassium hydroxide derived from ashes). 


Surfactants (cleansers). Surfactants can be replaced with other surfactants of the same group, that is, anionics with anionics, cationics with cationics, etc. Be careful when you do it: if you replace a surfactant, you will have to recalculate the active surfactant matter and adjust its percentage to meet the requirements of your formula. Check the Surfactants article for more information. 

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