Compendium of the most significant studies with reference to properties, intake, effects.

Bujak, T., Nizioł-Łukaszewska, Z., & Wasilewski, T. (2019). Sodium lauryl sulfate vs. sodium coco sulfate. Study of the Safety of Use Anionic Surfactants with Respect to Their Interaction with the Skin. Tenside Surfactants Detergents, 56(2), 126-133.

Abstract. As a result of growing awareness, consumers are increasingly interested in products that are safe on the skin and environmentally-friendly. This is one of the most important reasons for the very rapid development of the natural cosmetics segment which has been observed for several years now. Among the most commonly used anionic surfactants of natural origin are sodium lauryl sulfate (SLS) and sodium coco sulfate (SCS). As there are no unambiguous reports on the safety of using SCS, in this study an attempt was made to evaluate the effect of SCS on the skin. The results of the determination of the skin irritation potential (zein value) indicate that the analyzed parameter is approximately 15 % lower in SCS than in SLS. SCS has a stronger ability to interact with epidermal lipids and cause their elution from the skin, which in turn may damage the protective epidermal barrier. The results obtained during the evaluation of the effect produced by the analyzed substances on the metabolism of human keratinocytes (HaCaT) show that after 4 h of incubation with the studied groups of compounds there was a significant decrease in cell proliferation. The highest decrease in cell metabolism was demonstrated for SLS.

Komorowska, J. K. (2021). The effect of selected surfactants on the biomechanical properties of skin cells (Doctoral dissertation, Katedra Biotechnologii Środków Leczniczych i Kosmetyków).

Abstract. Every year, the awareness of the society about caring for health increases. Body care is no longer limited to the use of shampoo or soap, but covers the entire range of cosmetics. A cosmetic can be any chemical substance or mixture intended for external contact with the human body. One of the main ingredients of cosmetics are surfactants. In the composition of cosmetics, you can find many types of surfactants used in various concentrations. Due to the type of substance and its amount in a given product, cosmetics may have various effects on human skin, including side effects. The aim of the study was to investigate the effect of selected surfactants - sodium dodecyl sulfate (SDS), sodium lauryl ether sulfate (SLES), sodium coco sulfate (SCS) and disodium 2-sulfolaurate (SFA) on the properties of skin cells. Mainly HaCaT keratinocytes were used for the tests, and corneocytes collected directly from the patient were used for one of the tests. A series of experiments and microscopic observations were performed: cell viability tests such as the MTT, LDH and NR test; study of cell membrane damage by measuring protein concentration in supernatants and staining of cells with crystal violet followed by observation using an inverted field microscope; study of the effect of test substances on the production of interleukins and metalloproteinases by cells using the ELISA test; observation of apoptotic and necrotic changes in cells using fluorescence microscopy; observation of cells’ cytoskeleton by fluorescence microscopy and study of changes in cell viscoelasticity in real-time after the exposure to the tested substances using a quartz crystal microbalance with the function of tracking the energy dissipation. Both type and concentration of the surfactant used affect the properties of the tested skin cells. On the basis of the MTT test results the selected concentrations were used in the subsequent experiments. The LDH test did not show a significant effect of surfactants on the decrease in cell viability, while the NR test indicated SFA as the mildest, and SDS and SCS as the most irritating substances. By measuring the amount of protein in the supernatants, it can be shown that SFA has the least irritating effect on cells, whereas SCS, SLES, and SDS are more irritating substances. Crystal violet staining of both keratinocytes and corneocytes confirmed this result. Observation of apoptotic and necrotic changes in cells showed no major effect of SFA and SCS, and also significant changes after SDS application on cells. Based on the ELISA tests for the amount of interleukin and metalloproteinases, it can be concluded that SDS and SLES are more irritating to keratinocytes than SCS and SFA. Observation of cells by fluorescence microscopy and observation of the influence of tested surfactants on the viscoelastic properties of cells in real-time confirmed the previously obtained results.

Fiume, M., Bergfeld, W. F., Belsito, D. V., Klaassen, C. D., Marks, J. G., Shank, R. C., ... & Andersen, F. A. (2010). Final report on the safety assessment of sodium cetearyl sulfate and related alkyl sulfates as used in cosmetics. International journal of toxicology, 29(3_suppl), 115S-132S.

Abstract. Sodium cetearyl sulfate is the sodium salt of a mixture of cetyl and stearyl sulfate. The other ingredients in this safety assessment are also alkyl salts, including ammonium coco-sulfate, ammonium myristyl sulfate, magnesium coco-sulfate, sodium cetyl sulfate, sodium coco/hydrogenated tallow sulfate, sodium coco-sulfate, sodium decyl sulfate, sodium ethylhexyl sulfate, sodium myristyl sulfate, sodium oleyl sulfate, sodium stearyl sulfate, sodium tallow sulfate, sodium tridecyl sulfate, and zinc coco-sulfate. These ingredients are surfactants used at concentrations from 0.1% to 29%, primarily in soaps and shampoos. Many of these ingredients are not in current use. The Cosmetic Ingredient Review (CIR) Expert Panel previously completed a safety assessment of sodium and ammonium lauryl sulfate. The data available for sodium lauryl sulfate and ammonium lauryl sulfate provide sufficient basis for concluding that sodium cetearyl sulfate and related alkyl sulfates are safe in the practices of use and concentration described in the safety assessment.

Morvan, J., Saluden, M., Agasse, V., Barbot, F., Cardinael, P., Bouillon, J. P., & Decock, G. (2006). Characterisation of ethoxylated fatty chains of anionic surfactants and determination of residual ethoxylated fatty alcohols. Analytical and bioanalytical chemistry, 384(6), 1409-1415.

Abstract. Bachus et al. recently described a new derivatisation method using 2-furoyl chloride for the characterisation of mixtures of polyethoxylated alcohols and their corresponding sulfates. This paper deals with the control of the derivatisation steps; hydrolysis and extraction conditions were optimised. The method is extended to the characterisation of alkyl sulfosuccinates, alkyl sulfoacetates and alkyl phosphates and to the analysis of residual polyethoxylated alcohols in surfactants. Extraction of non-ionic compounds using solid-phase extraction cartridges was performed before derivatisation. Residual amounts of alcohol were determined in five commercial anionic surfactants. Moreover, direct derivatisation without preliminary SPE in the same anionic surfactants proved to be efficient for dry samples.

Bujak, T., Zagórska-Dziok, M., & Nizioł-Łukaszewska, Z. (2020). Complexes of ectoine with the anionic surfactants as active ingredients of cleansing cosmetics with reduced irritating Potential. Molecules, 25(6), 1433.

Abstract. For many years, an increasing number of diagnosed atopy and skin problems have been observed. For people affected by the problem of atopy, the selection of skin care products, including cosmetics, is extremely important. Cleansing cosmetics, due to their ability to cause skin irritations and disturb the hydrolipidic barrier, can increase problems with atopic skin. New solutions to reduce the effects of these products on the skin are very important. In this work, the effect of ectoine on the properties of anionic surfactants was analyzed. Based on model systems, analysis of the effect of ectoine on the irritating effect of four anionic surfactants and their ability to solubilize model sebum was performed. Antioxidant activity was also evaluated, and cytotoxic studies were performed on cell cultures. It was shown that the addition of ectoine to the anionic surfactant solutions improves its safety of use. After introducing ectoine to the surfactant solution, a decrease of irritant potential (about 20%) and a decrease in the ability to solubilize of model sebum (about 10–20%) was noted. Addition of ectoine to surfactant solutions also reduced their cytotoxicity by up to 60%. The obtained results indicate that ectoine may be a modern ingredient that improves the safety of cleansing cosmetics.