Test your formulation knowledge

As an educator I find giving students practical exercises a powerful, interactive and fun learning tool.  

Our fun formulation exercises are aimed at formulators (homecrafters and chemists alike) and have proved very popular.  Go on, have a go and comment in this link with your thoughts on what the errors might be and how to fix them. ⁣

The next day after posting in instagram we edit this post on our website to write up the answers.



Tap water  Almost everyone who participated in our instagram quiz on 4 April 2020 spotted this obvious error!  Tap water contains metals and other chemicals which can cause auto-oxidation, has a destabilising effect on the emulsion and makes our products harder to preserve.  Distilled or deionized water is the way to go (deionized has the ions removed but not always the bacteria which need to be filtered out).  We should aim for: 1-10 microsiemens generally in conductivity and less than 10 CFU/G/Ml by TVC.
Glycerin  Glycerin can make emulsions feel sticky at high concentrations. Most people prefer a concentration of around 2-3%.
Sodium hyaluronate   Sodium hyaluronate is available in different molecular weights.  The one in this formula (1.5 million daltons) is very high and used at just 1%, let alone 3%, would make the formula extremely viscous.  The concentration of sodium hyaluronate in this formula should therefore be greatly reduced.
D4  D4 stands for “cyclotetrasiloxane”.  D4 is more commonly known as “cyclomethicone”.  (As an aside, cyclomethicone is the generic name also for: cyclotrisiloxane (D3), cyclopentasiloxane (D5), cyclohexasiloxane (D6), and cycloheptasiloxane (D7)).  As D4 is volatile, it should go in the cool down phase.  However, should D4 be in this formula at all?  Cyclotetrasiloxane is already banned in many Countries for wash-off products and in the EU, the law has recently gone further (reference: The Commission Regulation (EU) 2019/831 of 22 May 2019 amending Annex II to Regulation (EC) No 1223/2009). As a consequence chemists are in the process of removing this ingredient from their formulas.   For the situation in the USA click here
Glyceryl stearate  Not many formulators in the instagram post spotted that the emulsification system in this formula is greatly lacking. Glyceryl stearate is a weak low HLB emulsifier and creates water-in-oil emulsions.  Emulsifiers are surface active molecules which are hydrophilic at one end, and lipophillic at the tail.  So emulsifiers are partially oil and partially water soluble in the same molecule.  Cetearyl alcohol is, obviously, an alcohol (short hydrocarbon chain alcohols are soluble in water), however, being C16 and C18 it has a long carbon chain (the longer the chain, the more lipophilic) and so despite the OH group cetearyl alcohol isn’t water soluble enough to make it a “proper” emulsifier.  Therefore it can only be classed as a weak emulsifier at best.  This means we do not have a strong emulsifier in this formula and for ease of formulation and simplicity (long story – water in oil post explaining this coming up), we need this formula to be oil in water, rather than water in oil.   A high HLB emulsifier (creates oil-in-water emulsions), such as ceteareth-20, polysorbate 60, steareth-21, or methyl glucose sesquistearate should therefore be added at the appropriate concentration.  For more information on emulsifiers, how much to use, how to pair them up and which ones are effective click here.
Niaciamide  Many formulators commented in our instagram post that niacinamide should be in the water phase.  A few also commented that pH 5.7 is too low and I referred those commenters to this informative article by Kind of Stephen.
Allantoin  Most commenters spotted this obvious error.  Allantoin needs heat to dissolve and the concentration of 1% is too high, however, a little tip, if you would like to get more than 0.5% into your formula adding trimethylglycine and also urea can increase solubility.
Potassium sorbate  Only a couple of formulators spotted the pH error here.  Organic acids are more active at a lower pH, so the pH of 5.7 is too high and should be adjusted to pH 4.5-5.  This would mean, there is more organic acid in its undissociated form so it is more effective (it can transfer into the micro-organism cell).
Rose essential oil  This one was an easy error to spot for most formulators and most commented that they would reduce the concentration to 0.02%.  This formula would fall into IFRA category 4C or 5, depending on the area you apply the emulsion.  For the correct answer, it is advisable to check the supplier’s IFRA Certificate of Conformity for the particular type of rose essential oil you are using as they do vary.  For more information on essential oil usage rates click here.
Lack of water soluble high yield polymer  A couple of formulators spotted that the addition of xanthan gum would help strengthen this emulsion.  We have written in depth about this here and step 3 here.
Additional notes  Even with the above key errors corrected, this formula could be improved a thousand different ways!  With hundreds and thousands of ingredients out there, and everyone having their unique formulation style, favourite emulsifiers, favourite esters, rheology modifiers and the like, no formulation need be the same.  This is what I love about what we do – art, science and creativity all in one to produce a unique creation which represents who we are.