I know today's post sounds a bit more scientific than usual, but I wanted to share with you all a common problem that we cosmetic formulators face with natural ingredients.
Rancidity is a chemical decomposition process that occurs naturally in oils and butters. In the formulation of natural products, it is a phenomenon that we must prevent because it represents a threat to skin health. Also, rancid oils lose most of their properties (significant loss of fat-soluble vitamins, among others).
This degradation can occur in three different ways:
Hydrolysis: triglycerides separate into fatty acids and glycerin. It usually occurs in high humidity environments.
Polymerization: lipid molecules tend to group into larger molecules. It happens more frequently if we store our oils in rooms with high temperatures (above 25 degrees Celsius).
Autoxidation: lipids tend to release hydrogen and feed on oxygen. This particular case is one of the most dangerous because it occurs very quickly (chain reaction).
In the laboratory, we have the right tools to determine if our oils have become rancid. At home, on the other hand, we can quickly tell because they smell quite bad. Think of the smell of rancid butter or when the fruits of female ginkgo biloba species fall to the ground, they release butyric acid which produces a very unpleasant smell.
Can oxidation be prevented?
The answer is yes. I recommend starting by storing our products away from light and heat sources and never using metal containers; glass is always the preferred 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 it is exposed to air, the better.
New natural cosmetics contain the correct dose of antioxidants to protect the formulas. The most common is tocopherol, but there are studies that show positive results (in vitro) for some essential oils, such as lemon, thyme, sage, and oregano.
The amount of antioxidant must be calculated correctly based on the amount of oils and their chemical structure. If less than the necessary amount is added, oxidation will occur, but if it goes beyond the correct dose, it could increase the chances of oxidation, which is called pro-oxidation. This can be one of the most challenging steps when creating a formula and it takes time to get it right. That is why I always repeat "Natural product formulation is a science. Not an experiment."