Pyrethroid-mediated skin sensory stimulation characterized by a new behavioral paradigm.

Occupational exposures to pyrethroids have been associated with skin sensory effects characterized by transient itching/tingling sensations. This effect had not been detected in "Draize" skin irritation tests and exists in the absence of visible skin irritation. The objective of this investigation was to develop an animal model to study this phenomenon. Guinea pigs were treated with pyrethroid solutions on one side of their shaved back and control substances on the other side. The animals responded by licking, rubbing, scratching, or biting the test sites and activity was quantified by counting the number of times the animals responded to pyrethroid or control treated sites. Animals responded to pyrethroid more than to control substances and this behavioral activity was apparently maximum during the first hour and essentially over by the fourth hour after treatment. The sensory response did not directly correlate with overt visible signs of skin irritation. However, a chemical irritant (oil of mustard) was able to restimulate the behavioral activity when applied within 24 hr after pyrethroid application. Skin sensory stimulation produced by cyano-containing synthetic pyrethroids was significantly greater than that produced by a non-cyano-containing pyrethroid. This behavioral model provides a quantitative means to evaluate pyrethroid nonerythematous skin sensory stimulation.