An animal model for altering the irritability threshold of normal skin

Theory behind conditioned hyperirritability (autoeczematization) predicts the lowering of the irritation threshold in the presence of a pre-existing dermatitis. We have attempted to develop an animal model that parallels the syndrome seen in num. Groups of 10 guinea pigs were shaved and depilated; irritation thresholds to benzlkonium chloride und trichloroacetic acid were determined using I cm diameter open patches. Reactions were scored 24 h later on the basis of erythema and induration. Animals having as little as 1.56 cm2 of skin acutely inflamed with a known irritant had lowered irritation thresholds lo the same irritant on normal skin at remote sites (P <0.01). Mild irritation of a much larger surface area produced the same effect (p <0.01). More extensive, severe dermatitis did not lower the irritation threshold further Acute dermatitis induced by a contact allergen (DNCB) lowered the irritation threshold of normal skin to the same level as that obtained with irritants (p <0.01) Induction of chronic cutaneous ulcers 3–4 cm in diameter lowered the irritation threshold of normal skin to the same point defined by the acute studies (p 0.01), These results indicate that an acute irritant or contact dermatitis. as well as chronic skin ulceration. may alter the reactivity of unaffected normal skin to exhibit; i heightened response to irritation. This model appears lo differ from that seen in humans, in that it more extensive or chronic dermatitis did not further heighten the susecptibility to irritation.