Reapplication of the Type IV Hypersensitivity Quantitative Risk Assessment to Assess Ingredients Used on Canines

A quantitative risk assessment (QRA) framework to assess the risk for the induction of human skin sensitization from exposure to contact allergens has been successfully developed and applied. So far, the QRA has not been applied in a canine risk assessment for establishing concentration limits of ingredients with Type IV hypersensitivity potential. Outlining this risk assessment is critical, as shampoos are known to cause allergic contact dermatitis (ACD) in canines. Additionally, humans have developed ACD after washing their dogs with dog shampoo. To address this gap, we conducted a thorough literature review on canine Type IV hypersensitivity and identified potential differences which might demand an adaptation of the QRA. We summarize data from the literature demonstrating that all four key events (KE) in the skin sensitization adverse outcome pathway (AOP) are present in dogs as they are in humans, guinea pigs, and mice. The hazard potential of sensitizers for canines is compared with the established sensitization QRA framework for humans. The limited collective evidence suggests that dogs are not more susceptible to sensitizers than humans; therefore, safety-defined concentration limits from Type IV hypersensitivity risk assessments for humans can be re-applied to canines so long as their unique exposure considerations are factored in. Using the principles in this review, one can evaluate chemical sensitizers to support the safe development of new topical formulations for canines. The result of applying our current best approaches for assessing ACD to canine products should protect both the pet and the owners.