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The low-down on what constitutes a cosmetic serum.

April 4, 2012

Ok so I have to admit that I was confused this morning, not that that’s unusual – I always set myself some pretty steep challenges but this was different. Tomorrow I have to do a class about serums.  To be more precise I want to talk about what a serum is, the types of ingredients that go into them and how they can be formulated to work.  Sound simple?   Well you are one up on me!  I have a cupboard full of serums that people have sent me to try over the last year and all of them are different. Some are oily, some are clearly so emulsified that they look like creams, others look like my all time favourite – whale sperm (every new formulation I make looks a bit spermy so this is a term of endearment – I have NEVER milked a whale for sperm so can only imagine…..).  So forgive me for asking but what SHOULD a serum look like?

I did some google research first (as you do)…..

“A serum is a targeted treatment that is applied topically to the area to be treated. Typically, a serum is the most potent of the products in a line and is used as a layering formula”


“The clear liquid that is separated from the blood cells and platelets”. in conjunction with Vichy.

“A serum is a product typified by its rapid absorption and ability to penetrate into the deeper layers of the skin, together with its non-greasy finish and intensive formula with a very high concentration of active substances.

“While facial serums can give you added moisture, the main reason you’d want to use a facial serum is to get added nutrients into deeper layers of your skin that a regular moisturizer is not able to reach”

and decided on the following as my definition of a serum:

  • They should look ‘light’ in texture and be non-clogging.
  • They should go into the skin quickly, dragging the actives with it.
  • They should contain a potent mix of actives for targeted skin repair.
  • They should be able to penetrate into the skin more deeply than a moisturizer.

So, how would you go about making something like that?

Well, if we break it down we get somewhere close to working out what to put in to get the results that we require out.   Here are the rest of my teaching notes on the subject – if you want to discuss the finer points with me then feel free to drop me an e-mail or facebook comment.

Deconstructing a formulation.

Light Texture.

  • Many are Oil-Free so get their texture and body from emollients or silicones.   Suitable examples of emollients that are easy to get hold of would be:
    • C12-15 Alkyl Benzoate
    • MCT Oil
    • Dimethocone
    • Oleyl Oleate
    • Vegetable squalane.

Go into the skin quickly dragging actives with it.

Potent Mix Of Actives.

Penetrate the Skin.

  • There are many ways to enhance skin penetration but  not all of them are suitable for such a light-weight, oil-free base.

A good way to drive water soluble actives through in this scenario is to use humectants that work via osmosis moving actives from high water content (the serum) to lower water content (the skin) to even them out:

  • Betaine
  • Hyaluronic Acid
  • Urea
  • Sodium PCA
  • Beta Glucan Powder
  • 1,3 Propane Diol (natural origin)
  • Propylene Glycol (1,2 propanediol)
  • Butylene Glycol.
  • A serum could contain a myriad of functional ingredients depending on the specific claims that the product wishes to make. Just check if they are oil or water soluble first. Here are some water soluble options that are pretty commonly found.
    • Peptides
    • Fruit Acids
    • Argania Spinosa
    • Matrixyl
    • Nature Lift
    • Oatmeal
    • Any liquid herbal extract
    • Sodium Ascorbyl Phosphate
    • Niacinamide

The only way to tell if these are working would be to run some in-vivo trials using the base with and without the delivery system (humectant) to see what results you get.

  • Oily actives would not be delivered through the skin this way and as such you would have to look at a different delivery system for actives such as:
  • Vitamin A
  • Vitamin C Liquid (Ascorbyl Tetraisopalmitate)
  • Vitamin E
  • Alpha Lipoic Acid
  • Coenzyme Q10

If you wanted to put these into the same serum as the water soluble actives you would have to form an emulsion.  A micro-emulsion would be best for a serum so that it maintained its lightness and functionality rather than a traditional coarse emulsion.  Otherwise you could make a separate serum that was water-free for the oil soluble components.   This is what many brands now do and is why some ‘serums’ available on the market look like oils.



Micro-emulsions have different objectives. The high percentage of emulsifiers causes a very fast penetration respectively permeation of the active agents into the skin due to its powerful impact on the skin barrier. This is an advantage especially for the pharmaceutical sector, i.e. when systemic therapies with drugs are intended. In the field of skin care this may rather cause disadvantages as emulsifiers severely disturb the integrity of the skin barrier layers (see KI 2000 (12), 112-113: emulsifiers – looking for alternatives). In the cosmetic sector micro-emulsions are mostly used in skin cleansing, e.g. in form of fat-containing cleansing gels, shower gels and foam bath products.

Making a micro-emulsion is too complex to discuss here but just in case you are really interested here is some more info:

To give you an idea the emulsifiers used to make microemulsions are more like solubilisers. They are typically surfactant-like in their structure and have a very good solubilizing power.   Caprylic/ capric triglyceride is an example of a micro-emulsion forming ingredient that is easy to get your hands on. 

They should have little or no odour.

As serums are designed to be both highly active and highly mobile through the skin the addition of fragrance is not recommended. However, as some active ingredients do smell bad an odor mask may be appropriate.

So, there you have a quick overview of a serum.  When I teach this class I also end with a formulation and talk about the importance of skin feel and perception – you may need to add more ingredients to achieve the perfect balance between activity and feel and that can be tricky but fun.



2 Comments leave one →
  1. Dr. Anas dar permalink
    February 24, 2013 1:58 am

    I like that but i need more information about whitening serum contaning kojic acid and stuff?


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