What role does water play in skincare products?

Lotions, moisturizers, cleansers, deodorants, makeup, oral hygiene products... water is the foundation of virtually all types of cosmetic products. Often considered the main ingredient compared to all others and the first term at the top of the INCI list, a skincare product can contain from 60 to 95% water depending on the category. For instance, rinse-off hair care products, shower gels, serums, or cleansers can contain up to 95% water, while balms and ointments may only contain 60%.

Only mixtures of vegetable and/or mineral oils, "greasy" treatments (lipsticks, sun oils, etc.), perfumes, solid formats, and anhydrous galenics (powders, blushes, etc.) can do without it.

Water is primarily used as a solvent. In other words, it helps to dissolve water-soluble active ingredients. It also plays a role in the extraction and production of many natural raw materials, sometimes in combination with other solvents (ethanol, glycerin, etc.). In addition to controlling their fluidity to facilitate their application and distribution on the skin or hair, water mainly allows to control the consistency of skincare products. For example, when combined with emulsifiers, water can be mixed with thicker-textured ingredients, like butters, waxes, and oils, to form emulsions. Similarly, in the case of a gel, water is used to serve as a base for gelling agents to establish the structure of the skincare product.

Some cosmetic skincare formulas replace the standard water added to the formulation with water obtained from plant sources (hydrosol), thermal water, sea water, or cellular water rich in minerals and trace elements, thus becoming an active ingredient.

What about the quality of water used to formulate cosmetic products?

The water used in the formulation of cosmetics is not ordinary tap or bottled water. Only water free of toxins, pollutants, and microbes, as well as low in calcium and heavy metals (lead, copper, etc.) is used in the formulation of cosmetic products. The water used for this purpose is also referred to as "distilled water", "deionized water", "demineralized water", or "purified water".

Purified and sterile, water confers no specific properties to the product, thus it is referred to as a 'dead' ingredient.

How is the water used in cosmetic care products obtained?

While it is the basic ingredient in most cosmetics, water undergoes various treatments to achieve sterilized, pure, and cosmetic-grade quality before being incorporated into the skincare formula. This process is done to meet high purity requirements according to cosmetic standards, such as those defined by the European Pharmacopoeia.

• Water Softeners: This technique uses an ion-exchange resin to specifically replace unwanted ions, namely calcium (Ca2+) and magnesium (Mg2+), with sodium (Na+) which are less reactive. However, the resulting water is not completely demineralized, as it still contains sodium ions and possibly other minerals. Nevertheless, this helps to reduce the hardness of the water.

• Deionization: This process aids in the production of water that has been stripped of its ionic mineral impurities through an ion exchange principle. This involves passing the water through a tank equipped with two ion-exchange resins: a negatively charged cationic resin and a positively charged anionic resin. During the passage, an ion exchange occurs and the ions of the minerals dissolved in the water are attracted to the resins.

• Microbiological Disinfection: To destroy microorganisms (bacteria, fungi, viruses), water is either subjected to exposure to UV rays, or to the addition of ozone (ozonation), which is a powerful oxidizing agent, or, less commonly, to the addition of chlorine (chlorination).

• Distillation: This treatment method helps to remove most contaminants from water (nitrates, lead, etc.) to produce purified water. During this process, the water is boiled in a boiling chamber until it evaporates. The steam produced is then captured and condensed, leaving behind certain microbiological contaminants, organic compounds (calcium, etc.), and non-volatile molecules that cannot transform into gas particles (steam), as they have boiling points lower than that of water.

• Reverse Osmosis (membrane filtration/nanofiltration): In this system, pre-filtered water is subjected to osmotic pressure, thereby forcing water molecules through a semi-permeable membrane equipped with nanometric pores. During the flow process, suspended particles, microorganisms, soluble salts, and macromolecules present in the raw water are retained on the other side of the membrane, resulting in water that is almost demineralized and purified.

Even though it has been filtered and sterilized, the use of water can have an impact on the preservation of cosmetic formulations. As a result, water-based cosmetic products must also contain preservatives to inhibit microbial growth and prevent contamination.