I know today’s post sounds a bit more science geek than usual but I wanted to share with you, a common issue we natural formulators face with plant based ingredients.
Rancidity is a process of chemical decomposition naturally occuring in oils and butters. In natural skincare formulation is a phenomenon, that we must prevent because it poses a threat to the skin’s health. Also rancid oils loose most of their properties (significant loss of fat-soluble vitamins amongst others).
This degradation can happen in three different ways:
Hydrolysis: The triglycerides are separated into fatty acids and glycerin. It usually happens in high humidity environments.
Polymerisation: The lipid molecules tend to group into bigger molecules. It happens more frequently if we stock our oils in high temperatures rooms (above 25 degrees celcius).
Autoxidation: The lipids tend to release hydrogen and feed on oxygen. This particular case is one of the most dangerous ones because it happens very quickly (chain reaction).
In the lab we have the right tools to establish if our oils have gone rancid. At home, instead, we can spot it quickly because they smell pretty badly. Think about the smell of rancid butter or when the fruits of female species of gingko biloba fall to the ground, they release butyric acid leading to a very umpleasant odour.
Can oxidation be prevented?
The answer is yes. I recommend to start by storing our products away from light and heat sources and never use metal containers, glass is always the prefered material. Avoid constant humidity. If you keep them in your bathroom, a good option is to store them in a cabinet.
Once you start using the product, keep using it. The less time exposed to air, the better it is.
Modern skincare contains the right dose of anti-oxidants to protect the formulas. The most common one is tocopherol but there are studies that show positive results (in vitro) for some essential oils, including lemonbalm, thyme, sage and oregano.
The amount of anti-oxidant must be properly calculated based on the amount of oils and their chemical structure. If you add less than the quantity needed, oxidation will happen, but if you go beyond the right dose, it might increase the chances of oxidation, it is called pro-oxidation. This can be one the most challening steps while creating a formula and it takes time to get it right. Little wonder I always “Natural Product Formulation is a Science. Not an Experiment”