[Histamine reactivity of affected and unaffected skin in endogenous eczema and in chronic allergic contact dermatitis].

In 30 patients with atopic dermatitis and 40 with allergic contact dermatitis in the chronic stage intracutaneous tests were performed with 0.1 ml histamine 1:10,000 in affected and non-affected skin. The erythematous and wheal reactions were compared with 40 age- and sex-matched controls. The diameters of the erythema and wheals were significantly reduced in affected and non-affected skin of the atopic dermatitis (p less than 0.01). In allergic contact dermatitis only the erythema of the affected and non-affected skin was reduced (p less than 0.05), but not the wheal reaction. The erythematous reaction was, however, less reduced in non-affected skin than in the affected one of the allergic contact dermatitis (p less than 0.05). The reduced histamine reactivity seems to be a typical basic mechanism in atopic dermatitis. It is suggested to be due to the histamine mediated immune modulation and the increased release from mast cells, leading to a refractory behaviour of histamine receptors of the blood vessels like in tachyphylaxis. It is interpreted as a secondary phenomenon in allergic contact dermatitis. Although the histamine reaction shows differences for the groups of patients, it is not suitable to discriminate single cases.