Irritant susceptibility and weal and flare reactions to bioactive agents in atopic dermatitis. II. Influence of season

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Abstract
Many atopic dermatitis (AD) patients have exacerbations of their skin disease in winter. These exacerbations may be caused by non-immunological 'non-specific' factors, such as low sun exposure and low temperature. To date, the influence of season on non-specific skin reactivity in AD has not been studied. The aim of the present investigation was to assess the influence of season on two skin parameters which may be used as quantitative measures of non-specific skin reactivity in AD: (i) susceptibility to repeated epicutaneous irritant (sodium lauryl sulphate, SLS) exposure, and (ii) weal and flare responses to intracutaneous injection of bioactive agents (codeine, FMLP, histamine, methacholine, substance P, trypsin). Four of 16 AD patients had dermatitis which was more severe in November than in July. Susceptibility to SLS was increased in November, both in AD patients and in control subjects. AD patients were more susceptible to SLS than control subjects in both July and November. Pre-exposure barrier function and skin hydration were reduced in November. The increased irritant susceptibility in November may be attributed to reduced barrier function, reduced skin hydration, and/or absence of the beneficial effects of ultraviolet light on cellular targets beneath the stratum corneum. Flare responses to codeine, methacholine, substance P and trypsin were also increased in November compared with July, especially in AD patients. However, smaller flares were observed in AD patients than in control subjects, in both July and November. Flare values were negatively correlated with dermatitis severity, probably because of down-regulation. Weal responses did not show a clear seasonal variation. Hence, susceptibility to epicutaneous irritants and reactivity to intracutaneously injected bioactive agents are parameters which may be used to monitor season-dependent changes in non-specific skin reactivity.