Physical irritant contact dermatitis (PICD) is a common occupational dermatosis with multiple types and many mechanisms involved in its development . The diagnosis is primarily based on a history of exposure to a known irritant and negative patch test results to exclude contact allergy.
The basic concept of PICD is physical skin damage without preceding or concomitant chemical irritation and sensitization, respectively. Initial PICD is characterized by a local inflammatory reaction, i.e. erythema, scaling and induration. PICD is accompanied by barrier disruption, i.e. stratum corneum changes. However, in vitro excessive physical insults, such as irradiation with 3,000 rad of X-ray, heating at 90°C for 3 min, freezing at -196°C for 60 s or repeated placement in an extremely dry or humid condition, do not cause any change in the stratum corneum functions . Because the viable skin is more vulnerable to environmental
conditions than the stratum corneum, most of the stratum corneum abnormalities develop after environmental insults have induced an underlying inflammation. Stratum corneum abnormalities in inflamed skin are detectable as changes in the content of chemical mediators: physical insults enhance only in vivo the ratio between the proinflammatory interleukin (IL) 1 and its receptor antagonist (IL-1ra). Therefore, barrier disruption is one of the major pathogenic mechanisms of PICD.
However, occupational skin disease caused by physical irritants is still a relatively underresearched area . Further, the external environment seldom involves exposures to one single physical irritant: it is often a cumulative exposure to one or more mechanical and climatic irritants, respectively, and other influences (irradiation) with synergistic and antagonistic effects (fig. 1) .
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