Constituents of Human Scent as Perceived by Wilderness Search and Rescue Area Dogs

Abstract

It has long been believed that human scent detected by search dogs results from volatile organic compounds (VOCs) generated by bacteria that metabolize skin secretions and shedded skin cells, termed skin rafts. However, recent laboratory research has shown that human breath VOCs constitute a large proportion of the human volatilome and are an important component of how dogs perceive human scent. We investigated the perception of skin (cutaneous) and breath samples as constituents of human scent by certified search and rescue area dogs. Dogs (n=6) searched tunnels in a three-alternative, forced-choice test. In qualification trials, one tunnel was connected to a tent with a human volunteer while two remained empty. After reaching 80% accuracy with whole human scent, dogs were given four probe trials whereby an air flow system pumped into one tunnel (1) breath, (2) air from exposed skin (cutaneous), (3) both (breath + cutaneous), or (4) none (negative control). We scored the dogs’ latency to respond and whether a dog made a trained final response, change of behavior, or no response. All dogs responded to the breath + cutaneous and breath conditions with a trained final response or change of behavior. Breath only and breath + cutaneous led to similar response latency and probability to respond (p ≥ 0.5). In contrast, both the latency to respond and the probability of responding to the cutaneous only condition was significantly longer (p = 0.001) and significantly less (p = 0.03), respectively, than to breath + cutaneous. These data demonstrate that scent from human breath is an important and salient component of how wilderness SAR area dogs perceive human scent and suggest that the “skin raft” model of human scent be reevaluated.