Sodium Lauryl Sulfate (SLS) is a commonly used ingredient mainly in cosmetics and detergents. From a chemical point of view, Sodium Lauryl Sulfate belongs to anionic surfactants. It is a sodium salt of lauryl sulfuric acid. The common name of this compound is sodium lauryl alcohol sulfate. The CAS no. that allows for unique identification Sodium Lauryl Sulfate is 85586-07-8.
Sodium Laureth Sulfate, SLES, is very similar to Sodium Lauryl Sulfate (SLS) in terms of physical and chemical properties and application in cosmetic and detergent products. The main difference is in the production process of these compounds: in case of SLS lauryl alcohol is only sulphated with SO3 and neutralized with NaOH, while in case of SLES it is first ethoxylated and only then sulphated and neutralized. Oxyethylation, commonly known as ethoxylation is a process in which ethylene oxide is attached. This process is critical as it makes SLES less irritating to the skin than SLS. Both of these compounds are perceived on the market as the main factors causing severe skin irritation. This is not entirely true, because it is possible to develop really mild formulations with SLS or SLES. However, this requires a thorough knowledge of surfactants, their specific properties, and especially their behaviour in the presence of other surfactants. Surfactants are specific chemical compounds that behave completely differently when alone than if combined with other ingredients. And yet cosmetic formulations contain lots of various ingredients. It turns out that the addition of Cocamidopropyl Betaine to a formulation containing SLS or SLES greatly reduces its irritating potential. It is also very important to select the appropriate concentrations of individual components. There is a visible trend on the market to eliminate SLS and SLES from cosmetics. However, this is not possible, as products containing SLES and SLS still constitute the largest part of the flushable cosmetics market. Global companies know this very well and continue to rely on SLES and SLS. Just check the labels on washing products such as shampoos, shower gels, etc.
Sodium Laureth Sulfate, similarly to Sodium Lauryl Sulfate, has very good washing, foaming, emulsifying and thickening properties in the presence of salt (NaCl). These are the best anionic surfactants in terms of properties and so far not as effective and at the same time economically viable alternative has been found. Of course, there are many other anionic surfactants that are used in sulfate free formulations, but these are less effective compounds (must be used in higher concentrations), are not easy to formulate and (often) are much more expensive.
Lowering the surface tension of aqueous solutions
SLES and SLS, like all other surfactants, have the ability to lower the surface tension at the water-air interface. As a result, the wettability increases and water can reach everywhere, and so the surfactant particles contained in it surround and separate dirt particles from the surface being washed and the proper washing process takes place. In order for the water to start washing, it is mandatory to reduce its surface tension, because as its tension decreases, the wettability of water increases, i.e. its ability to penetrate the surface as the basic factor that affects washing. If the surface tension is appropriately lowered and the water reaches everywhere, the proper washing process begins and the surfactants contained in water (in the washing solution) surround, separate and remove dirt particles from the surface being washed.
Foaming properties
Shampoos, shower gels, bath lotions, etc. – all these are preparations that have to foam well. The foam itself is not responsible for washing, although there is such a myth that if something does not foam, it means that it washes poorly. This is not true. Among surfactants, there are compounds with excellent cleaning properties which do not foam. The foam facilitates spreading of the preparation, e.g. shampoo, on the hair and thus supports the washing process, but is not directly responsible for it. Generally, the best foaming compounds are anionic surfactants such as SLES and SLS.
Removal of impurities, i.e. detergency
The ability to remove dirt by surfactants such as Sodium Lauryl Sulphate is also inextricably linked to the structure of the SLS molecule – as well as other features, such as the ability to create abundant and stable foam. Detergency is related to the reduction of surface tension by a specific washing agent. When analysing the composition of basic cleaning agents, such as liquid soaps or shampoos, water is almost always mentioned as first (in the INCI system, the ingredients are listed depending on the content in the preparation: from the highest to the lowest), followed by a surfactant, e.g. Sodium Lauryl Sulfate. It allows the dirt particles to be wetted and surrounded by surfactant particles. The alkyl chain, or the “tail” of the detergent, penetrates deep into the dirt molecule, and the hydrophilic part, or the “head”, is combined with the water. Thanks to this, it is much easier to detach the dirt from the surface and remove it.
Sodium Lauryl Sulfate can be found in most cosmetic and hygiene products available in beauty supply stores. Its special physical and chemical properties determine its application in many areas of the cosmetics industry, etc. The most important products containing Sodium Lauryl Sulfate are:
Sodium Lauryl Sulfate has been recognized as a safe ingredient in hygiene products. Please remember, that it is a strong detergent and people with skin diseases or high skin sensitivity may experience allergic reactions, dryness, itching, burning and general irritation of the epidermis or hair follicles. Not everyone will experience such symptoms, but many consumers consciously choose SLS-free products. Sodium Lauryl Sulfate, like any anionic surfactant, is involved in the processes during which mainly fat-like substances (but also lipophilic and hydrophilic substances) and other impurities are removed from the surface of skin. The epidermal hydrolipid coat contains numerous fatty substances that can be removed by washing with detergents. This results in a significant loss of water through the epidermis, leading to dry skin and disturbed secretion of sebum. Nevertheless, the appropriate selection of the ingredients and their amounts allows for a significant reduction of the irritating effect on the skin, even in preparations containing SLS.
The growing demand for cosmetic products, detergents and industrial cleaners is a major contributor to the increased demand for Sodium Lauryl Sulphate. The growth on the SLS market, which has been observed for several years (this tendency is expected to continue in the future), results from the growing public awareness of health and personal hygiene[1].
Globally, European countries have the most significant share in the consumption of Sodium Lauryl Sulphate. According to estimates, the European market will grow dynamically in the future and may reach a share of over 17% by the end of 2027 (according to www.globenewswire.com).The main driving factor is the growing sales of cleaning agents and other detergents. There is also a growing demand for cleaning agents dedicated for industrial applications, supported by strict regulations on cleanliness and hygiene in the workplace[2].The Asian and Pacific markets are also promising. It is considered the fastest growing and the largest in terms of the use of Sodium Lauryl Sulphate. The development of consumption is observed in the countries of this region, which is likely to increase the demand for Sodium Lauryl Sulphate. Currently, China is the fastest growing market in terms of soaps, washing powders and synthetic detergents. A similar trend occurs also in India. The Indian beauty and personal care market has seen steady growth recently, driven by the increasing emphasis on healthy living and hygiene[3].Investments with the aim to market products containing SLS are likely to have a positive impact on the Asia-Pacific market as the detergent sector revivals. Similarly, due to the growing demand for personal care products, Africa and the Middle East is a market with a potential increase in the use of Sodium Lauryl Sulphate[4].
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