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Most people talk about pheromones as if there is one single chemical. Wrong. There are many different types of chemicals that act as smell-signals.
Not all pheromones are related to sex - pheromones can communicate many things. Ants use them to mark trails to food. When dogs mark fireplugs, they leave a lot of information about themselves - think of it as the neighborhood bulletin board for the canine community.
There are at least 3 types of sex-related pheromones in mammals that have been characterized by biologists:
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- Steroid Pheromones - based on Androstenone and other steroids. Most commercial pheromone sprays fall in this category.
- Copulins - based on simple organic acids or short chain fatty acids, these communicate information about the metabolic state of an organism, including some factors related to sexual state.
- Major Histocompatibility Complex (MHC) factors - somehow, animals can use smell to sense genetic identity, which tends to discourage in-breeding. Women who smell clothing worn by men with a similar MHC describe the scent in terms of their father or brother. When women smell clothing from men with very different MHCs, they are more likely to describe it as masculine or sexy. It isn't clear what scent-based differences arise from a person's genetic MHC profile. (article en route)
