In-vitro and in-vivo studies have supported antimicrobial, anti-inflammatory, and other biologic properties of hypochlorous acid (HOCl), which has led to its use in the treatment of skin wounds, pruritus, diabetic ulcers, and some inflammatory skin disorders. Research has also shown that the physiochemical properties of HOCl after application to skin are highly dependent on both pH and formulation stability. In this review, the authors discuss a core HOCI formulation (Microcyn® Technology, Sonoma Pharmaceuticals, Petaluma, California) that is stable for up to two years, noncytotoxic, and pH-neutralized to augment therapeutic activity, skin tolerability, and stability. The authors summarize relevant study outcomes and potential modes of action related to this core HOCI formulation, as well as describe its ready-to-use vehicles that are approved and available for topical application.

Hypochlorous acid (HOCl), a naturally occurring molecule that is a component of the human innate immune response, is recognized as a major active component of bleach and demonstrates antimicrobial properties supported by both in-vitro and in-vivo studies.1–9 One important function of HOCl in host immunity is its release by neutrophils to destroy pathogenic organisms (i.e., respiratory burst). Over time, a variety of anti-inflammatory and other biologic properties of HOCl have led to applications for wound healing, pruritus, and diabetic ulcers, as well as applications for the management of some inflammatory skin disorders, such as seborrheic dermatitis and atopic dermatitis (AD).8–18 What has also come to light is that the physiochemical properties of HOCl and its impact after application to skin are highly dependent on both pH and formulation stability.8,11 The use of HOCl in the clinical setting is supported by a substantial body of research, which has led to the use of a core formulation—available in ready-to-use, approved topical vehicles —that is stable for up to two years, noncytotoxic, and, importantly, pH-neutralized to augment therapeutic activity, skin tolerability, and stability.8,11,18,19 This core formulation (often referred to in the literature as a superoxidized solution or, sometimes, slightly acidic electrolyzed water) has been termed and marketed as Microcyn® Technology (Sonoma Pharmaceuticals, Petaluma, California; also referred to in some publications as Dermacyn™ from Dyamed Biotech Pte Ltd., Singapore).8,11,20–22 In this article, we‘ve summarized the available studies related to the core formulation, its available vehicles for topical application, its potential modes of action, and in-vitro and in-vivo study outcomes.

HOCl has been incorporated into topical formulations due to antimicrobial, anti-inflammatory, immunomodulatory, and wound healing properties.1,6,8,10,11,17,20–22 The central microbicidal role of HOCl as a component of an innate immune response to combat pathogens within human phagocytic cells (i.e., neutrophils, monocytes, macrophages) is a pivotal concept in appreciating the potential therapeutic value of HOCl.11 The antimicrobial activity of HOCl is not that of a conventional antibiotic but rather an agent that is directly toxic to microbial cells, including many gram-positive and gram-negative bacteria (e.g., Staphylococcus aureus, Pseudomonas aeruginosa) and their biofilms.1–7 However, it is important to understand the relative balance of HOCl versus other reaction byproducts that are produced in equilibrium after the HOCl solution is applied. Formulation stability, pH, and resultant chemical reactivity influence the relative concentrations of HOCl, as compared with other byproducts (e.g., hypochlorite [-OCl]), which directly impacts the magnitude of antimicrobial activity, clinical effects, and potential irritancy of topical HOCl formulations.11,20,21 In highly acidic pH (pH5.5), much of the HOCl is converted to -OCl.11 HOCl stability is optimized over a pH range of 3.5 to 5.5.11 Stabilized/pH-neutral HOCl is superior in terms of antimicrobial activity to nonstabilized HOCL and acidified bleach in vitro, including against hypochlorite-resistant strains.5,11,21 This cumulative fundamental understanding of the physiochemical properties of HOCl led to the development of the stabilized and pH-neutral core formulation of HOCl solution mentioned previously (Microcyn® Technology) and its incorporation into different vehicles that allow for ease of application in clinical practice.8,22 Existing studies evaluating the antimicrobial effects of HOCl are summarized in Table 1.

Existing studies evaluating mechanisms of action of HOCl