Chemistry Behind Skin Care: A Glimpse into Moisture

We recently interviewed Dr. Chiou, a chemist at L’Oreal, in order to gain some insight into the world of cosmetic chemistry. Dr. Chiou is originally from Taiwan, and she attended Taiwan National University to receive her B.S. in Chemistry. Later, she worked towards her doctoral degree in Bioinorganic Chemistry at  the University of Minnesota and completed her postdoctoral studies at Harvard University. Afterwards, she worked for Unilever, specializing in laundry and dishwasher detergents research. Dr. Chiou eventually went to L’Oreal to begin her current career in raw material technology where she focuses on finding new raw material technologies to use in cosmetic products, such as skin care formulations. During our interview, we discussed various topics, connecting chemistry to the world of cosmetics.

Hydration

Dr. Chiou works closely with developing moisturizers, which are important for skin hydration. She explained how we feel dry during the winter due to the cold weather and low humidity; in these conditions, our bodies want to reach balance with the atmosphere, and this is essentially what dehydrates our skin. However, moisturizers combat this problem with many important components. First, moisturizers must contain a humectant, a substance that is able to hold onto the water in the product. Humectants are also responsible for attracting water from lower layers of the skin and even the atmosphere. Their chemical structure attracts water from the atmosphere and binds to the molecule. Humectants have multiple alcohol (hydroxyl) hydrophilic sites (like esters or ammonium (NH4+) groups) that form hydrogen bonds with other water molecules. Since hydrogen bonding is a strong intermolecular force, the humectants and water are able to improve moisture retention by minimizing water loss from evaporation.

Figure 1: Humectants are hydrophilic substances, containing hydroxyl groups. They are composed of polar molecules, and the dipole-dipole interactions between these molecules and the hydrogen-bonding water molecules allow an attraction to occur, thus allowing for moisture retention.

                 

       Hydroxyl Group                                               Ester Group                            Ammonium Group

How do you keep the fragrance in the product as long as possible? How can you test a fragrance?

In our previous interview with Mr. Herman, we discussed several interesting points pertaining to the chemistry behind fragrances. Dr. Chiou was able to tell us about certain protocols for testing fragrance stability, which relates to the shelf life and compatibility of a fragrance with other compounds.

When testing a product that contains a fragrance, cosmetic scientists will place the product in different temperature chambers for a period of 2 to 3 months. Often, the product is tested at 5, 25, 27, and 45° Celsius, as these temperatures mimic freezing, room, body and cooking temperatures, respectively. During this time, the samples can be monitored, and at the end of the tests, trained experts can sniff the product to determine how much the smell has reduced. Also, researchers can see if the scent interacted with the product. For example, the scent may cause the product’s color to change, meaning that the synthesized scent chemical may be impacting the product, which is something that should be avoided.

By heating up the product, cosmetic chemists are actually able to accelerate the processes that occur in a product over time. In fact, by heating a product to 45° Celsius for 2-3 months, one can see how a product will last for about 3 years on the shelf.

Essentially, an increase in temperature helps to increase the rate of a reaction. In any chemical reaction, the reactant molecules must collide hard enough so that they have enough energy to overcome the activation energy barrier. This relates to the kinetic energy of molecules; in any sample, molecules will have an average kinetic energy, and this average kinetic energy will determine whether or not the reaction will have enough energy to occur. However, not all of the molecules in a system have the same amount of kinetic energy; only those with a higher amount of energy will have enough energy to react. However, upon increasing the temperature, more molecules will contain greater amounts of energy. This increases the frequency and intensity of the collisions, making it easier for the molecules to overcome the activation energy. Therefore, by heating a cosmetic product, one can see what would normally happen to it over a much longer period of time.

Figure 2: In order for a reaction to occur, the reactants must collide with enough energy to overcome the activation energy barrier, and this process can be accelerated by increasing the temperature of the reactants.

A look into the future: Nanotechnology and Cosmetics

L’Oreal holds many patents in nanotechnology. However, cosmetic chemists must be careful with nanotechnology. In 2013, the European Union, a regulatory body for cosmetics, mandated that cosmetic companies label any products containing nanoparticles, since the effect of nanomaterials on the human body is not truly known; at such a small size, the physical behavior of materials is very different from what we know. For example,titanium dioxide (TiO2) is normally white, but when reduced into a nanoparticle, it becomes transparent. Therefore, it is a component of many sunscreens. However, the effects of TiO2 on the body are not fully known; in fact, animal studies show that TiO2 can be retained in the liver and kidney.

In fact, nanoemulsions are commonly used in cosmetics to aid in the delivery of active ingredients. These emulsions are similar to normal emulsions, which consist of particles that can be measured in micrometers. Very often, emulsions consist of oil droplets dispersed in water, and upon contact with the skin, this emulsion breaks apart, allowing for the release of an active ingredient. However, nanoemulsions do not form spontaneously. Energy is required to form a nanoemulsion. Since free energy is absorbed and not released in the formation of these emulsions, they are not thermodynamically stable, even if they consist of the same exact chemicals found in normal emulsions.

Conclusion:

A major aspect of cosmetic skin care is the ability to keep moisture within the skin. Chemistry explains how a simple lotion can rejuvenate dry skin and bring out one’s natural beauty. Humectants have a unique chemical structure capable of attracting moisture to the skin. The future of cosmetics is looking towards nanotechnology, which can improve skincare and makeup. The field of chemistry is constantly advancing, and nanoparticles have the potential to provide a great impact on the future of cosmetics.

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