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The Hardening Phenomenon in Irritant Contact Dermatitis: Cosmetic Implications

By: Howard I. Maibach, MD, University of California School of Medicine, San Francisco and Shannon A. Watkins, MD, Yale New Haven Hospital

Posted: October 30, 2009, from the November 2009 issue of Cosmetics & Toiletries.

Irritant contact dermatitis (ICD) is common and poses a significant problem in high risk populations including hairdressers, health care workers, metal- working professionals and cleaning specialists.¹ In fact, as many as 35% of junior hairdressers develop ICD during their first year in training. Most cases of ICD are resolved in spite of continued exposure, allowing individuals to continue with their work. However, some cases develop into chronic ICD, which often manifests on the hands as red, dry, scaly and fissured skin.¹

When ICD resolves without intervention, it transitions through a process known as hardening or accommodation. Generally, this self-resolving phenomenon is simply accepted amongst laborers and clinicians but its mechanism remains elusive. While extensive research and a textbook opine on the pathogenesis of irritant contact dermatitis and its related factors, research is sparse pertaining to factors that contribute to non-irritated and non-sensitive skin.²

This is likely because the institution of modern science largely focuses on the mechanisms of active disease rather than those of non-disease and illnesses that self-resolve. Much can be learned, however, by studying these self-healing processes such as the hardening phenomenon. This overview briefly documents the pathogenesis of ICD, focuses on the current understanding of hardening in ICD, and highlights possible productive areas of research. A better understanding of the research to date on the hardening phenomenon, summarized in this paper, will hopefully lead to management advances for the treatment of ICD.

In relation, the authors suspect that the management principles discussed here are equally relevant to cosmetic formulations, including surfactants, steroids and mascaras. Many consumers experience marginal skin irritation after the use of cosmeceutical products. Therefore, a better understanding of the physical and immunologic changes that occur as the skin adapts to irritants could lead to therapies that enable consumers to better tolerate these products as well as the development of less irritating products in the future.

Pathogenesis of ICD
ICD is defined as a multifactorial disease that results from skin exposure to an irritant.³ It is a complex phenomenon that depends on endogenous and exogenous factors such as individual genetics, the nature of the irritants and the physical environment.⁴ Irritants cause a non-specific reaction upon contact with the skin that disrupts skin barrier function, causes direct cellular damage to the epidermis, and results in the release of pro-inflammatory mediators.4 Different chemicals can target different components of the epidermis and physical properties of the irritant, such as its PKa, as well as contribute to irritancy potential.⁵ The culmination of these interrelated processes leads to the clinical manifestations of ICD, which are variable.³