The hardening phenomenon in irritant contact dermatitis: an interpretative update

Abstract

Irritant contact dermatitis (ICD) is common and poses a significant problem in high-risk populations. In most cases, ICD resolves despite continued exposure in a process known as 'hardening', allowing individuals to continue with their work. Those who cannot clear ICD develop chronic ICD, which is a significant source of emotional, physical, and financial distress for affected individuals. While hardening is well known among labourers and clinicians, its mechanism remains to be elucidated. Much can be learned from the study of self-healing processes like the hardening phenomenon. This overview briefly documents the pathogenesis of ICD, focuses on the latest advances pertaining to the hardening phenomenon in ICD, and then highlights potential avenues of productive research. A better understanding of the 'hardening' process in the skin will hopefully lead to advances for the treatment of ICD.Key words: accommodation; contact dermatitis; hardening; hyporeactivity; irritant; irritant contact dermatitis; skin hyporeactivity. # Blackwell Munksgaard, 2009. Accepted for publication 9 November 2008Irritant contact dermatitis (ICD) is common and poses a significant problem in high-risk populations. As many as 35% of junior hairdressers developed ICD during their first training year (1). In most cases, ICD resolves in spite of continued exposure in a process known as 'hardening', allowing individuals to continue with their work: 90% of hairdressing apprentices who initially suffered from hand eczema during their training period had clearance of the eczema by the end of the training. The eczema persisted in only 10% (2). Those who cannot clear ICD develop chronic ICD. Chronic ICD often manifests on the hands as red, dry, scaly, and fissured skin (3) and is a significant problem for those working in high-risk occupations such as hairdressing, health care, metal work, and cleaning (3). Due to lost workdays and emotional distress, chronic ICD has severe economic implications for workers, companies, and social security systems (4). Most ICD resolves without intervention in a process known as 'hardening' or 'accommodation'. The existence of this self-resolving phenomenon is accepted among labourers and clinicians, but its mechanism remains elusive. While extensive research and a textbook opine on the pathogenesis of irritation and its related factors, research is sparse pertaining to factors that contribute to non-irritated and non-sensitive skin (5). 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. The process of 'hardening' is an example of one of these self-resolving phenomena.This overview briefly documents the pathogenesis of ICD, focuses on the latest advances pertaining to the hardening phenomenon in ICD, and then highlights possible productive areas of research. A better understanding of the 'hardening' process in skin will ho...

Individual Susceptibility to Occupational Contact Dermatitis

“…In the study of de Jongh et al 47) some individuals showed improving of the skin barrier in the third week of exposure to SLS which is in a good agreement with several other studies [50][51][52][53][54] . The mechanisms of skin hardening are not elucidated yet, however some studies found that skin hardening was associated with the levels of proinflammatory mediators and ceramide 1 expression in the stratum corneum 49) .…”

“…3-wk exposure) irritation, lesser or no correlation between skin barrier function and irritation effect has been found, which is consistent with the findings from the field studies 14,47,48) . One possible explanation for the discrepancy between single and repeated exposure might be accommodation of the skin barrier ("hardening") during repetitive irritation in some individuals 48,49) . In the study of de Jongh et al 47) some individuals showed improving of the skin barrier in the third week of exposure to SLS which is in a good agreement with several other studies [50][51][52][53][54] .…”

Case Presentation: Trick or Treat?

“…However, research shows that ICD and ACD are more similar than previously thought (Watkins & Maibach, 2009). ICD often underlies other forms of dermatitis, including ACD.…”

Irritant Dermatitis

“…This is known as a "hardening" effect, in which the skin adapts to the topical irritant. The molecular mechanisms are not completely elucidated; however, changes in stratum corneum thickness and function, downregulation of the production of inflammatory mediators, and alteration in the production of stratum corneum lipids have been observed (Watkins and Maibach, 2009;Welfriend andMaibach, 2008). et al, 1997;Fluhr et al, 2005;Rothenborg et al, 1977).…”