Surfactants in Cleansers: Their role in removing dirt, soil, and makeup from the skin through chemical mechanisms - LM SKINCENTRE (2025)

• LM SKINCENTRE

Surfactants are the cornerstone ingredients in virtually all cleansing products, including bar cleansers, body washes, facial cleansers, and shampoos. Their primary function is to effectively remove dirt, soil, sebum (skin oil), sweat, microorganisms, and makeup from the skin and hair surfaces through a combination of unique chemical mechanisms. The term “surfactant” is an abbreviation for “surface-active agent,” which accurately describes their ability to modify the surface tension between different phases, such as oil and water, allowing them to interact with and remove various types of impurities.

The effectiveness of surfactants stems from their unique molecular structure, which is amphiphilic, meaning each molecule possesses both a hydrophilic (water-loving, polar) head and a hydrophobic (oil-loving, non-polar) tail. This dual affinity allows surfactant molecules to orient themselves at the interface between water and oily substances, which are typically immiscible. When a cleansing product containing surfactants is applied to the skin with water, the hydrophobic tails of the surfactant molecules are attracted to and associate with the oily dirt, sebum, and makeup residues on the skin’s surface. Simultaneously, the hydrophilic heads are attracted to and interact with the surrounding water.

As the concentration of surfactant in the water reaches a certain level known as the critical micelle concentration (CMC), the surfactant molecules begin to aggregate into spherical structures called micelles. In these micelles, the hydrophobic tails cluster together in the interior, creating an oily core, while the hydrophilic heads face outwards, interacting with the aqueous environment. This process, known as emulsification, allows the oily substances trapped by the hydrophobic tails within the micelle’s core to become suspended in the water. Once emulsified, these previously water-insoluble impurities can be easily rinsed away from the skin during the washing process.

Surfactants also facilitate cleansing by reducing the interfacial tension between oil and water. This reduction in tension allows water to more effectively wet the skin’s surface and penetrate oily soils, aiding in their detachment. Furthermore, after the oily soils are removed from the skin, surfactants help to solubilise them in the water, preventing them from redepositing back onto the skin during rinsing.

Surfactants used in cleansers can be classified into four main categories based on the electrical charge of their hydrophilic head:

Anionic surfactants have a negatively charged head and are generally good at foaming and lathering, providing effective cleansing by removing sebum and oily dirt. Examples include sodium lauryl sulfate (SLS) and sodium laureth sulfate (SLES). While effective cleansers, some anionic surfactants can be harsher on the skin and may disrupt the skin barrier if not carefully formulated.

Cationic surfactants have a positively charged head and are often used in hair conditioners for their ability to neutralise static charge and soften the hair. They are less commonly used as primary cleansing agents in skin cleansers due to their potential for irritation.

Amphoteric (zwitterionic) surfactants possess both positive and negative charges on the same molecule. They are generally milder and well-tolerated by the skin, often used in facial cleansers and baby shampoos. Cocamidopropyl betaine is a common example. Amphoteric surfactants can also help to improve the lather quality and mildness of anionic surfactant-based formulations.

Non-ionic surfactants have an uncharged, polar head. They are typically very mild and well-tolerated by sensitive skin but may not lather as abundantly as anionic surfactants. Examples include polyglucosides and sorbitan esters. The choice and combination of surfactants in a cleanser formulation are critical for achieving the desired balance between effective cleansing and skin mildness. Formulators carefully select surfactants and adjust their concentrations to optimise cleaning efficacy while minimising potential disruption to the skin’s protective lipid barrier and reducing the risk of irritation. Newer synthetic surfactants are often designed to be milder to the skin by having less interaction with skin lipids.