When we talk about cleaning products, we often talk about surfactants. Discover all the surfactants available, the problems associated with them and ways to formulate natural hygiene products.
Surfactants: definition, functions and classification
By definition, surfactants are molecules with both an affinity for: water (hydrophilic part) and oil (lipophilic part). In other words, surface-active molecules allow the mixing of two phases which do not have, at the beginning, any affinity for each other. This particularity allows them to ensure a cleaning function by clinging to the fatty substances, which are then carried away in the rinsing water. They thus play the role of emulsifier and washing agent at the same time.
Surfactants can be used as :
- Detergent: to remove impurities
- Wetting: facilitates the spreading of the liquid on a solid surface (e.g. the skin)
- Foaming : allows to create bubbles
- Solubilizer : helps to solubilize a non-miscible ingredient in a medium (example : perfume)
- Emulsifying : facilitates the mixing of non-miscible ingredients together (example : water/oil)
Each surfactant has several of these properties, but they are not all present with the same intensity in the same molecule. Some surfactants are more detergent, wetting and foaming, while others can be more emulsifying or solubilizing.
There is therefore a wide variety of surfactants on the market, suitable for the formulation of all kinds of products: soaps, shower gels, shampoos, creams, make-up remover… Most surfactants are of synthetic origin but some, increasingly used, are of natural origin.
From a chemical point of view, surfactants are classified into 4 groups: anionic, cationic, amphoteric and non-ionic. These groups are defined according to the positive or negative charge of their hydrophilic part (attracted by water).
Classification of surfactants
- Definition: negatively charged hydrophilic part
- Main property(ies): foaming detergent
The anionic surfactant is the most common. More expensive, it has a good detergent and foaming activity.
- Definition: positively charged hydrophilic part
- Main property(ies) : wetting, emulsifying
Cationic surfactants have an affinity with keratin (found in hair in particular), on which they form a smooth film. This type of surfactant is mainly used in after-shampoo care.
- Definition: hydrophilic part carrying the two charges, the nature of the charge varies according to the PH (cationic in acid medium and anionic in alkaline medium).
- Main property(ies): properties of anionics and cationics but to a lesser degree
This type of surfactant is mainly composed of betaine. They are generally used in shampoos, conditioners and detangling hair care products since they have detangling and smoothing properties.
- Definition: hydrophilic part with no charge
- Main property(ies): wetting and solubilizing
This type of surfactant is widely used in make-up removal products (micellar waters, lotions or milks). Their foaming power is however less powerful, but allows to create a light foam.
Undesirable effects of surfactants
Anionic: Anionic surfactants are known to be drying and among the most irritating. However, it is important to remember that conventional soap contains an anionic surfactant, which is created naturally during the saponification process. This is the mixture of vegetable oil and soda. However, this one remains natural and biodegradable, which is not the case of the most widespread anionic surfactant: the SLS or Sodium Laureth Sulfate. This powerful surfactant has a very foaming power, which belongs to the large family of “Sulfates”.
Cationic : Cationic surfactants are often known to be irritating to the eyes. Another constraint for formulators: cationic and anionic surfactants cannot be mixed, as their opposite charges attract each other forming insoluble complexes.
Amphoteric: Amphoteric surfactants are milder and less irritating than anionic surfactants, but have little foaming. These surfactants are rather well tolerated by the skin and do not sting the eyes. On the other hand, they are suspected of being endocrine disruptors, i.e. interacting with the hormonal system.
Non-ionic: Non-ionic surfactants are less aggressive on the skin than anionic surfactants, which are better tolerated. Even though they are gentler, some non-ionic surfactants can disrupt the hormonal system.
The galenic form of surfactants
Surfactants can be found in solid (powder) or liquid form (more or less fluid depending on the surfactant). The industry proposes mostly the liquid form because it facilitates the integration of the ingredient in liquid formulas which represent the majority of the market (shower gels, shampoos, creams, make-up removers…). However, since the rise of solid cosmetics (solid shower gel, solid make-up remover, solid shampoo), suppliers are offering more and more surfactants in powder or flake form. But for formulators, these surfactants are more complex to use because they are more concentrated and more reactive to interactions with other ingredients in the formula.
- Liquid formulas: use of surfactants pre-dispersed in liquid phase, they are less concentrated but easier to integrate and solubilize
- Solid formulas: use of surfactants in the form of powder or flakes, they are more concentrated and often require a heating phase to integrate them homogeneously with the other raw materials of the formula.
Surfactants of natural origin
Surfactants of natural origin are the compromise between price, efficiency and environmental impact. Globally, synthetic surfactants are derived from petrochemicals and are therefore relatively polluting because they are not very biodegradable and release chemical compounds that are sometimes more toxic than the initial product when they break down. However, there are alternatives made from renewable raw materials (vegetable such as copra, palm or rapeseed, sugars, amino acids, …), which present less risk to health and are more environmentally friendly.
The family of glutamates includes a set of surfactants made from fatty acids of coconut oil and an amino acid, glutamate. They are very soft surfactants, recreated from vegetable oils and sugar. These surfactants are non-toxic and fully biodegradable.
Saponin is a substance extracted from soapwort (herbaceous plant) or Panama wood (exotic tree). These plants or trees belong to the genus Sapindus, from the Latin sapo (soap) and indus (India). The extract of the soap tree (Sapindus trifoliatus) was exploited by the indigenous peoples of northwestern North America for hundreds of years. The soap nuts from this tree were crushed or whipped into a thick lather and used as a detergent. Some manufacturers still offer this type of 100% natural cleaning agent.
There are other vegetable emulsifiers such as soy lecithin, sunflower or rapeseed, or even proteins such as casein derivatives, which are very interesting for their emulsifying properties and their affinity with the skin.
On the whole, these soft and natural surfactants are expensive, they can cost 10 to 15 times more than classic petrochemical surfactants. They are rarely used in hygiene products because they are considered as “first necessity”. They are sold mainly in supermarkets at prices affordable to the general public.
From a formulation point of view, the two main difficulties encountered with these surfactants of natural origin (compared to synthetic surfactants), are:
- Foaming power: The foaming power of surfactants of natural origin is lower than synthetic ones which often requires combining them in order to maximize foam formation. This is a very important criterion for consumers. Indeed, in the mind of the consumer, a generous foam confers a feeling of effectiveness of the product and facilitates its use.
- Visual (transparency): It is more complicated to obtain transparent products with surfactants of natural origin because of their less good solubility in water. Moreover, the surface-active agents extracted from the plants often have the characteristic to be brown what colors the products.
Surfactants are often criticized and pointed out by the press. More and more consumers are studying the labels of their cosmetic products to track down undesirable ingredients.
Sulfates or sulfated surfactants have a powerful detergent action. They are commonly used for industrial floor and engine cleaning. They are an ingredient of choice for manufacturers because of their advantages: low cost, foaming, good for conservation and stabilized formulas wash.
What we reproach it: Sulfates are too “stripping” to be used daily. They destroy the lipidic film of the skin or the scalp, preventing it from being reformed from one washing to another. They therefore contribute to skin dehydration and an imbalance in sebum production, as the skin overreacts, causing blackheads and greasy roots.
The “SCI” surfactant
Sodium cocoyl isethionate, otherwise known as “SCI”, is a mild surfactant commonly used in solid cosmetics, especially in solid shampoos. This surfactant has multiple advantages for formulators: inexpensive, foaming, natural origin and conditioner for hair.
The problem with this surfactant is more in its manufacture than in its use. One of the components necessary to its manufacture (the ethylene oxide) is toxic for the man and the environment. This is why not all solid shampoos that use it can be certified organic.
The ” CAPB ” surfactant
Cocamidopropry Betaine (CAPB) is an amphoteric surfactant derived from Coconut oil – most often from Copra oil – and Dimethylaminopropylamine (DMAPA) or Dimethylamine (DMA). It is an ingredient that has both a natural and petrochemical fraction. It is often used in shower gels and shampoos as a secondary surfactant. Cocamidopropry Betaine softens more aggressive surfactants like anionics. It has experienced an effervescence following the various controversies on sulfated surfactants.
What it is accused of: Due to the presence of residues of Dimethylaminopropylamine in the manufacturing process, various cases of skin allergies have been reported in recent years, particularly among certain professionals (hair salons). A North American study concludes that the allergy rate is around 6%. These allergies most often result in eczema and various contact dermatitis on the face, neck and scalp.
Cocamidopropyl betaine could react with other components to form more toxic or carcinogenic molecules. Thus, amines and esters can react and develop nitrosamines, highly carcinogenic substances. However, to date, we have very little information on the possible toxicity of this ingredient on humans.
The position of cosmetics organizations
It’s a professional association dedicated to natural and organic cosmetics that uses the COSMOS referential. This referential is the most demanding and it can be used internationally. The organization has a very clear-cut opinion on the ICS. It denounces an unfinished ecological approach, putting health and the environment at risk.
Cosmébio’s argument is that beyond the format of the cosmetic, a product composition that includes certain surfactants, such as sodium cocoyl isethionate (SCI) goes against a responsible approach. This surfactant, derived from coconut oil, is widely used in the solid cosmetics market. It is used to make the product foam. It is often marketed as a “green” ingredient despite its prohibition in the natural and organic certification, because of its manufacturing process which uses ethoxylation.
“The dangers associated with ethylene oxide for humans: a highly irritating and corrosive carcinogen for the skin and eyes. It therefore presents a direct risk to the worker in contact with this substance.”
The association adds that ethoxylation is a heavy process carried out in conditions of extreme temperatures and pressures. This process is also very polluting: it involves ethylene oxide which is very reactive and toxic.
Its toxicity is indirectly found in nature if the good practices of use are not respected. Moreover, the ethoxylated derivatives obtained can contaminate the environment with the presence of toxic impurities (1,4-dioxane, ethylene oxide, etc.) for micro-organisms and fish.
“Even if the final ingredient can be considered natural and gentle on the planet, what is the point if all the harm has been done since its creation?”, Cosmébio calls out and launching a “call to reason to manufacturers”.
Slow Cosmetique is an association that aims to bring together brands that make the effort to offer ecological, healthy and reasonable products throughout the design chain. The respect of the specifications of this association allows the brands to obtain a “Slow Cosmetic Label” and are thus referenced on the eponymous online sales platform (slow-cosmetique.com).
The Slow Cosmetics Association does not tolerate the presence of sulfated compounds such as ammonium or sodium laureth sulfates in the formulas of its labeled brands. Nevertheless, sulfated surfactants of the sodium or ammonium lauryl sulfate type, accepted by organic certifications (Ecocert, Natrue…) are therefore also tolerated by the Label. However, they must be present in an isolated or exceptional way in a range of products. It’s the same for the sodium coco sulfate.
Today, 70% of surfactants are still essentially derived from petrochemicals. But the cosmetics industry is looking for new ingredients that meet the expectations of users, i.e. ingredients from natural resources and respecting health and the environment.
The European surfactants market amounts to 2.5 million tons, and has good growth prospects in this post-COVID period (which has greatly stimulated concerns about personal hygiene and environmental cleanliness).
The challenge for manufacturers will be to find the right compromise between affordability, efficiency, naturalness and respect for the environment.
Also read our expert file on “How is a natural cosmetic product formulated?“.