While humans are highly dependent upon visual cues, when in close proximity smells also play a big role in sociosexual behaviors. There is an inherent difficulty in studying human pheromones because of the need for cleanliness and odorlessness in human participants. [17] The focus of the experiments on human pheromones has been on three classes of putative pheromones: axillary steroids, vaginal aliphatic acids, and stimulators of the vomeronasal organ.