We have learnt how to formulate a lotion, but what is and how to formulate a serum? 🙂
There are few rules to follow:
1) a serum is usually a very light lotion (this means usually 2%, maximum 4% fats),
2) it is typically fluid
3) it has a very high concentration of ACTIVE INGREDIENTS.
4) it doesn’t have to be heated (actually this is a consequence of the previous points)
5) the function of a serum is to give an extra boost of good ingredients to your skin (just to be clear: the function of a cream is to be emollient and hydrate to the skin… therefore wishing to create “the ultimate hydrating serum” is like expecting to bake the best cake in the world without an oven: if you want hydration, you make a cream… if you want to feed your skin with an extra-boost of vitamins, antioxidants, anti-aging ingredients and sooo on, you make a serum).
PHASE A – will still contain water, glycerin and a gelling agent (or not, but I will explain this later… so keep reading 🙂 ), but you will have to pay attention to which gelling agent you choose: you need to choose a gelling agent which won’t break down in presence of salts or other tricky ingredients (for example carbopol ultrez 21 is one of these difficult gelling agenta). For instance xanthan gum or hydroxyethylcellulose are good gelling agents for this purpose (in case of hydroxyethylcell. remember the gel is formed only at 70° so you will need to heat your water and, only when it is cooled down, proceed in the making of your serum).
PHASE B – the oil soluble ingredients have to be very few: 1.5 – 4% (maximum!). By this I mean that even your oil soluble active ingredients will be counted in the fat percentage of the serum: for example if you desire to add 1% of vitamin E (tocopherol), you include it in your “maximum 4% count” 🙂
But how to behave with these oily substances in order to have a smooth, silky and specially fluid serum? 🙂
You will need different emulsifiers from those which we have used up to now: you will need actually two emulsifiers (one lipophilic at 0.25% and one hydrophilic at higher percentage) which are liquid and don’t need to be heated!
There are many on the market. Actually you could even use a solubilizer to keep together the emulsion (solubilizers are substances which are used to solubilize small small portions of oils into a lot of water: generally they are surfactants. In case you have a solubilizer at home and you want to use it as a hydrophilic emulsifier: add the oily substances of the serum in your becher and, little by little, add drops of the solubilizer until all the solution in your becher becomes milky white. Then add this solubilized oils into your Phase A).
Just for the record: if you don’t add oily soluble ingredients more than 1-1.5%, you don’t even need to add emulsifiers or solubilizers. This is the easiest and most simple way to make a serum 😀 everything would go in just one phase 😉
PHASE C – actually the Phase C could almost be deleted since you can almost always add the active ingredients directly to the Phase A (do not add them only if you use hydroxyethylcellulose as gelling agent because in this case the Phase A has to be heated and active ingredients are thermolabile).
The percentage of ACTIVE INGREDIENTS in a serum can be extremely high.
Sometimes you could even make a serum using an active ingredient as a gelling agent!
An example is the enriched hyaluronic acid serum which you can find HERE: this is also very easy to copy because there is not even the need of adding an emulsifier.
Let me know if I forgot to explain something or you have any questions.
Have a great day! 😀