A pheromone is a secreted chemical that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual. There are alarm pheromones, food trail pheromones, sex pheromones, and many others that affect behavior or physiology.
Christopher Dubov matched people who smelled similar based on the pheromones they secreted. He got his ex-wife and dentist together.