_ are used as recognized member of the same specie or member of the opposite sex:

Explanation

Pheromones are substances which are secreted to the outside by an individual and received by a second individual of the same species. Many examples exist in animals but their role in humans remains uncertain since adults have no functioning vomeronasal organ, which processes pheromone signals in animals. Pheromones are chemicals that animals and humans use to communicate. Our bodies release pheromones through sweat, urine, semen, breast milk, and vaginal fluid. The theory is that these substances cause a reaction in the people around us. For example, pheromones might help us attract a mate.