Pheromones are produced by specialized glands found across the body, though the exact source depends on the species. In humans, the primary production sites are the apocrine sweat glands concentrated in the armpits and groin, along with sebaceous (oil) glands and secretions found in urine, saliva, and semen. In insects, entirely different gland systems handle the job. Here’s how it all works.
The Main Glands Behind Human Body Chemistry
Three types of skin glands can produce chemicals that become odorous: apocrine sweat glands, eccrine sweat glands, and sebaceous glands. Of these, apocrine glands get the most attention because they’re concentrated in the two body regions most associated with personal scent: the armpits (axillae) and the perineum, the area between the genitals and anus.
Sebaceous glands also play a role and are more widely distributed than most people realize. Specialized versions exist in the eyelids, ear canals, nostrils, lips, inner cheeks, breasts, foreskin, and the entire anogenital region. These glands secrete oily substances that carry chemical signals outward to the skin’s surface.
Beyond skin glands, potential signaling compounds show up at low levels in urine, saliva, semen, and vaginal secretions. Humans, like all vertebrates, release chemicals through their urine, breath, genitalia, and even anal excretions. These fluids act as vehicles that carry chemical compounds from inside the body into the environment, where another person could potentially detect them.
What These Glands Actually Produce
The leading candidate compounds in humans are a group of steroid-based molecules called 16-androstenes, which are structurally related to testosterone. The most studied of these is androstadienone, found primarily in male armpit sweat. Another compound, androstenone, is the same molecule that boars release to trigger mating behavior in sows. A third, androstenol, rounds out the group. Women appear to produce a distinct candidate compound called estratetraenol, which has an estrogen-like structure.
It’s worth noting that these are still called “putative” pheromones by scientists. Unlike in pigs or insects, where a single compound can trigger a clear, predictable behavior, human chemical communication is far more subtle and context-dependent. These steroid compounds are present in armpit sweat, urine, saliva, and semen, making them available for transfer between people, but their effects are not as dramatic as what you see in other animals.
Why Bacteria Are Part of the Process
Here’s something surprising: the chemicals your apocrine glands secrete are actually odorless when they first reach the skin. They only become the scent you recognize as body odor after bacteria living on your skin break them down.
Two main groups of bacteria colonize the armpit: Staphylococci and Corynebacteria. Odor formation is repeatedly linked to the population density of Corynebacteria specifically. These bacteria actively pull the odorless precursor molecules inside their cells, where specialized enzymes clip off parts of the chemical structure and release volatile, odorous compounds. For the sulfur-containing components of body odor (the ones responsible for the strongest smells), the process requires two sequential enzymatic steps inside Corynebacteria cells.
This means your personal scent is a collaboration between your glands and your skin microbiome. The glands supply raw material, and bacteria do the final chemical conversion. Different people harbor different bacterial communities, which partly explains why everyone smells a little different.
Your Immune Genes Shape Your Scent
Your unique body odor isn’t random. It’s influenced by a set of immune system genes called the major histocompatibility complex, or MHC. These genes help your body recognize pathogens, but they also appear to affect the chemical signals your body releases.
The connection was first demonstrated in mice, which reliably prefer the scent of mates with different MHC genes from their own. The same pattern has shown up in fish, which prefer water enriched with MHC-dissimilar chemical signals. In humans, several studies suggest people find the body odor of MHC-dissimilar individuals more attractive, a preference that could help ensure offspring inherit a broader, more diverse immune system.
The leading explanation is that specific MHC molecules bind small protein fragments called peptides, and these peptide combinations influence the volatile compounds produced at the skin’s surface. Your MHC genes essentially give your body odor a unique fingerprint that other people can unconsciously evaluate.
How Insects Produce Pheromones
Insects use a completely different system. Rather than relying on skin glands and bacteria, they have dedicated exocrine glands that synthesize pheromones through precise biochemical pathways.
Termites, for example, have at least five distinct gland types involved in pheromone production. The frontal gland produces alarm pheromones (and doubles as a chemical defense system). The sternal gland on the underside of the abdomen is the sole source of trail-following pheromones, the chemical breadcrumbs that let termites navigate to food sources. Sex pheromones come from both sternal and tergal glands.
Butterflies and moths build their pheromones from fatty acids using a two-step biochemical process. First, enzymes called desaturases modify the structure of common fatty acids like palmitic acid, inserting a double bond at a specific position in the molecule. Then, reductase enzymes convert the modified fatty acids into alcohols or aldehydes, the volatile molecules that drift through the air and attract mates. Male Bicyclus butterflies, for instance, produce their wing pheromones entirely through this fat-metabolism pathway, converting ordinary palmitic acid into hexadecanal through reduction and oxidation steps.
These insect pathways are remarkably conserved across species. The same core enzyme families that moths use for long-range sex pheromones also show up in fruit flies (for cuticular hydrocarbons) and bumblebees (for scent-marking compounds).
How Pheromones Are Detected
Many mammals detect pheromones through a specialized structure called the vomeronasal organ, or VNO, located in the nasal cavity. Mice, rats, and many other animals rely heavily on it. Humans do have a vomeronasal organ, and it’s present in the vast majority of adults, but it’s almost certainly vestigial. The current scientific consensus is that the human VNO has no operational sensory function.
So if the dedicated pheromone detector doesn’t work in humans, how would we pick up chemical signals at all? The answer appears to be the regular olfactory system. The same nose you use to smell food and perfume can also process the subtle chemical cues in body odor. This is part of why human “pheromone” effects tend to be mild shifts in mood or attraction rather than the hard-wired behavioral triggers seen in insects or pigs. You’re processing these signals through a general-purpose system, not a specialized one.