Cosmetic knowledge: The pH value in cosmetic products
In the last post, you learned why the pH value is important for the skin. Now we would like to take a closer look at the effects that the pH value has in cosmetics.
Active ingredients and fragrances
There are several active ingredients and raw materials in cosmetics that require a certain value to remain stable or to develop their effectiveness optimally. Some molecules cannot tolerate extreme pH values; for example, certain fragrances. Other raw materials, such as surfactants, also develop their best effectiveness or consistency at a specific pH value.
Just as there are substances that are sensitive to heat or light, there are also substances that do not tolerate extreme pH values – i.e., particularly acidic or particularly alkaline values.
Let's think "off-topic" about extreme products like sanitary cleaners or oven cleaners. The former are very acidic (they are intended to dissolve limescale), the latter are strongly alkaline (they are intended to dissolve baked-on grease). Have you ever wondered why these products are often scented with citrus notes and never, for example, with rose? This is because fragrance molecules that we associate with citrus notes (limonene and citral) remain stable in a strongly acidic environment.
In soap making, we have the other extreme. This involves working with strong alkalis, and many soap makers know: not every perfume oil can withstand this, and it will disappear or at least change color.
This is particularly important for preservatives. Many only work within a certain pH range or even lose their effectiveness if they are in an environment that is too alkaline. An example of this would be our Preblend Aqua.
One could say: The more acidic their environment, the stronger they work. Why is that?
Many preservatives are, chemically speaking, acids. If you increase the pH value of an acidic solution, individual acids are neutralized (dissociated) and are no longer present as acid, but as salt. The higher the pH value, the more acid molecules are no longer present as acid and thus no longer have an "acidic effect."
This is also the case, for example, with acidic active ingredients such as fruit acids (alpha-hydroxy acids = AHAs). An example would be our active ingredient Regenine.
How to measure the pH value in cosmetic products
To measure the pH value in an aqueous solution or in a water-containing cosmetic product, you can use our pH test strips, for example. These change color depending on the pH value. On the accompanying color scale, you can read which pH value your product has. This happens with an accuracy of approx. 0.5. So, this is not entirely exact, but certainly useful and sufficient for cosmetic manufacturing.
The more professional option would be the use of a pH meter. This measures the pH value by means of an electrode with an accuracy of 0.1. This is not strictly necessary for beginners, but it is very easy, fast, and precise, and thus leads to very satisfactory results. In the professional sector, a pH meter of this accuracy is indispensable. We recommend not choosing the cheapest device when purchasing, as these can have defects and can thus provide unusable results. Furthermore, it should be mentioned that a pH meter must be regularly maintained using a calibration liquid.
How to change the pH value in cosmetic products
If the pH value is higher than desired, it must be lowered with an acid. Citric acid is frequently used for this. But lactic acid or other organic acids are also fundamentally suitable. Our active ingredient Regenine also contains acids and can therefore also be used to lower the pH value. We always recommend using an acidic solution to lower the pH value gently step by step (drop by drop), as an overly rapid change in the pH value can lead to the impairment of the stability of emulsions.
For example, you can prepare a 50% citric acid solution by mixing water and citric acid 1:1. You can then store this solution for some time to adjust the pH value of your cosmetic products.
To increase the pH value, you need a base. Caustic soda or arginine is usually used here. The same applies here: Do not use pure sodium hydroxide (NaOH) or arginine because it changes the pH value too quickly and can very easily be overdosed.
You can prepare a 10% sodium hydroxide solution by mixing water and NaOH 9:1. This solution can also be stored (label well – corrosive!).
Arginine is not as strongly basic and must be dosed higher to increase the pH value accordingly.
Buffering (stabilizing) the pH value
It is possible that you set the pH value correctly, but it still changes afterwards. To prevent this, one should use a "pH buffer system." This is nothing other than an acid and its corresponding salt. E.g., citric acid and sodium citrate or lactic acid and sodium lactate.
But it is even simpler: you use an acid AND a base in your cosmetic product. Then a part of the acid neutralizes to salt and the buffer is created automatically.
So you can always use an acid (citric acid, lactic acid, Regenine, etc.) and a small amount of caustic soda in your product to adjust the pH value. Then you have a buffer and the desired pH value should (theoretically) also remain as you set it.
In practice, this means, for example: Always use citric acid + arginine.
Use as much citric acid as you need to adjust the pH value and a very small amount of arginine. Often, an amount of arginine equal to one-tenth of the citric acid amount is sufficient. For example:
0.1% citric acid + 0.01% arginine
Tip: If you are making 100g of cream, you might have problems weighing such small amounts of arginine. In this case, it might be better to dose the arginine by feel!