Pheromone cologne was an all-natural fragrance that Periwinkle the pixie had given to Vanity Smurf sometime before the events of "Papa's Big Crush." It was said to make those who smell the fragrance be attracted to whoever was wearing it. Vanity Smurf was intending to use it on himself so he could stay attracted to himself. However, Empath advised Vanity that it would more likely attract other Smurfs to him and thus dissuaded him from using the fragrance.
Vanity then gave it to Papa Smurf for safe-keeping, believing that the village leader would have no use for the cologne. However, Papa Smurf, who at the time was dealing with an attraction to Smurfette, was tempted to try out the cologne on himself and thus spritzed some on himself. However, the fumes of the fragrance had mixed with the chemicals that were in his laboratory, creating a thick mutagenic cloud that amplified Papa Smurf's desire for Smurfette and transformed him into a love-crazed muscular grotesquerie who chased after her.
Tracker, when he found out what had caused Papa Smurf's transformation during his search in the laboratory, suggested that Papa Smurf's transformation wouldn't reverse itself unless he had intimate interaction with Smurfette. To keep Smurfette from being violated, Empath had Brainy work on an artificial version of Smurfette's scent as well as a scent blocker for Smurfette to wear. He also had Tailor work on a Smurf-sized Smurfette doll so that Papa Smurf would be attracted to the doll and thus purge his feelings for her with the doll. This restored Papa Smurf to normal, though in the process it made him feel ashamed of ever having those kind of feelings for Smurfette. Fortunately, Smurfette wasn't offended by the attention Papa Smurf was giving her, but she did let him know that she could love him only as a father and nothing more.