Science Behind CAT1

Introduction

CAT1 contains a 1% concentration of cationic hyaluronic acid complex (Cationic HA Complex). During the wash process, this conditioning complex is adsorbed onto the skin, hence improving its smoothness and barrier function. Cationic HA complex also relieves irritation and dryness from cleansing agents.

Mechanism

Low molecular weight hyaluronic acid, a crucial component in Cationic HA Complex, hydrates the skin and reduces transepidermal water loss (TEWL) by penetrating deep into the epidermis and reaching the subcutaneous layers[1-2]. It also promotes the activity of caspase-14, a skin enzyme essential to produce natural moisturizing factor (NMF) that helps maintain both barrier and moisture retaining function of the stratum corneum[3].

Polyquaternium-10 (PQ-10) is a cellulose polymer in the Complex that makes it cationic (i.e., carrying a positive charge). On the other hand, the surface of stratum corneum, the outermost layer of the skin, is anionic (i.e., carrying a negative charge)[4-5]. Studies suggested that it can provide moisturizing effects and other skin protection properties through electrostatic interaction between their cationic charges and anionic skin even after thorough cleansing.

To remove dirt from the skin effectively, cleansing agents called surfactants are often added to cleansing products. Each surfactant molecule has a hydrophobic (water-hating) tail and a hydrophilic (water-loving) head. Surfactants first orient themselves so that the hydrophilic heads adhere to the water surface (called adsorption) and the hydrophobic tails point to the oil phase (or air). Strong interactions are formed between the surfactants and both phases, decreasing the interfacial tension and thus keeping the two phases together for an extended period. As more surfactants are adsorbed at the interface, the interfacial tension further decreases until the interface is saturated with surfactants. At this stage, the surfactant molecules combine to form spherical micelles in which the hydrophobic tails are pointed inwards and hydrophilic head outwards. The point at which micelles are formed is referred to critical micelle concentration (CMC), which indicates the efficiency of surfactants[6]. The lower the CMC value, the more efficient the surfactant, i.e., fewer amount of surfactants are required to reach maximum surface tension reduction.

Sebum and dirt are hydrophobic in nature. These materials are first solubilized in the hydrophobic core of the micelles, and then removed from the skin surface with the help of the water-soluble head groups[7]. However, harsh surfactants in cleansing products may bind with stratum corneum proteins, possibly leading to penetration of surfactants into deeper layers. This may cause discomfort such as irritation, itchiness, and dryness[8].

To address this problem, two mild surfactants are incorporated into the cleanser. Sodium cocoyl isethionate (SCI) is a mild anionic surfactant that is used in cleansers for those with high susceptibility to skin irritation. The size of SCI micelles is larger than average skin pore size, lowering its tendency to interact with skin proteins or penetrate the skin. This reduces the risk of surfactants damaging stratum corneum keratin and negatively affecting skin hydration[8-11]. Cocamidopropyl betaine is another mild surfactant incorporated in the cleanser. It is an amphoteric surfactant that contains both positive and negative charges, plus a hydrophobic chain on the same molecule. Studies showed that amphoteric surfactants minimize irritant activities and improve mildness of anionic surface active agents[8, 12].

It is suggested that anionic and amphoteric surfactants work in synergy to enhance the efficiency of a mixed surfactant system. Generally, the number of anionic SCI surfactants being adsorbed at the interface is limited as their negatively charged hydrophilic head groups repel each other. Cocamidopropyl betaine, which has zero net charge, can act as a mediator between anionic SCI head groups, thereby reducing repulsion between them and more surfactant molecules can be adsorbed at the interface. This lowers the interfacial tension, and thus the CMC value of the anionic-amphoteric surfactant system[13-14].

Formulator’s Note

Incorporation of various types of surfactants in a single formulation can provide superior cleansing properties and enhance the mildness of the overall formula. It is commonly misunderstood that the absence of foam in cleansing products would undermine its cleansing effect. In fact, the cleansing ability of a cleanser is not necessarily proportional to the amount of foam as that may be a result of foam dispensers or simply excessive surfactant in a formula. The key to a gentle and effective cleansing formula relies on the accurate amount of low-irritating surfactants that provides an electrostatic repulsion to lift the dirt from the skin effectively.

The skin’s mantle is slightly acidic, which is a major factor in maintaining skin barrier homeostasis and stratum corneum integrity. Thus the pH of the cleanser is designed to lie within 5-5.5, preventing skin irritation due to pH imbalance.

Reference

Essendoubi, M., Gobinet, C., Reynaud, R., Angiboust, J., Manfait, M. and Piot, O., 2015. Human skin penetration of hyaluronic acid of different molecular weights as probed by Raman spectroscopy. Skin Research and Technology, 22(1), pp.55-62.2. 2. 
Brown, T. J., Alcorn, D. and Fraser, J. R. E., 1999. Absorption of hyaluronan applied to the surface of intact skin. Journal of Investigative Dermatology, 113(5), pp. 740-746. 
Hashimoto, M. and Maeda, K., 2021. New Functions of Low-Molecular-Weight Hyaluronic Acid on Epidermis Filaggrin Production and Degradation. Cosmetics, 8(4), p.118.
Baspinar, Y. and Borchert, H.H., 2012. Penetration and release studies of positively and negatively charged nanoemulsions—is there a benefit of the positive charge?. International journal of pharmaceutics, 430(1-2), pp.247-252.
Lin, H., Xie, Q., Huang, X., Ban, J., Wang, B., Wei, X., Chen, Y. and Lu, Z., 2018. Increased skin permeation efficiency of imperatorin via charged ultradeformable lipid vesicles for transdermal delivery. International journal of nanomedicine, 13, p.831.
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Walters, R.M., Mao, G., Gunn, E.T. and Hornby, S., 2012. Cleansing formulations that respect skin barrier integrity. Dermatology research and practice, 2012.
Ananthapadmanabhan, K.P., Moore, D.J., Subramanyan, K., Misra, M. and Meyer, F.R.A.N.K., 2004. Cleansing without compromise: the impact of cleansers on the skin barrier and the technology of mild cleansing. Dermatologic therapy, 17, pp.16-25.
Fevola, M.J., Walters, R.M. and LiBrizzi, J.J., 2010. A new approach to formulating mild cleansers: hydrophobically-modified polymers for irritation mitigation. In Polymeric delivery of therapeutics (pp. 221-242). American Chemical Society.
Ghosh, S. and Blankschtein, D., 2008. Why is sodium cocoyl isethionate (SCI) mild to the skin barrier?–An in vitro investigation based on the relative sizes of the SCI micelles and the skin aqueous pores. International Journal of Cosmetic Science, 30(4), pp.310-310.
Solodkin, G., Chaudhari, U., Subramanyan, K., Johnson, A.W., Yan, X. and Gottlieb, A., 2006. Benefits of mild cleansing: synthetic surfactant based (syndet) bars for patients with atopic dermatitis. Cutis, 77(5), pp.317-324.
Zieba, M., Wieczorek, D., Klimaszewska, E., Malysa, A. and Kwasniewska, D., 2019. Application of new synthesized zwitterionic surfactants as hair shampoo components. Journal of Dispersion Science and Technology, 40(8), pp.1189-1196.
Noh, H., Kang, T., Ryu, J.S., Kim, S.Y. and Oh, S.G., 2016. Synergy effect for performance of anionic SDS/ADS mixtures with amphoteric and nonionic surfactants. Journal of the Korean Applied Science and Technology, 33(3), pp.449-458.
Sarkar, R., Pal, A., Rakshit, A. and Saha, B., 2021. Properties and applications of amphoteric surfactant: A concise review. Journal of Surfactants and Detergents, 24(5), pp.709-730.