Androsten refers to a family of steroid compounds built on the androstane skeleton, a 19-carbon structure shared with testosterone and other sex hormones. The most studied members are androstenone, androstenol, and androstadienone, each differing by small chemical tweaks but playing dramatically different roles in animal behavior, human sensory perception, and commercial agriculture. These molecules sit at an unusual crossroads: they are potent pheromones in pigs, they show up in truffles and human sweat, and they have been the subject of decades of research asking whether they influence human attraction and mood. The evidence behind those claims is more complicated than perfume marketing would suggest.
The Key Compounds and Where They Come From
When people say “androsten” without finishing the word, they are usually referring to one of three closely related molecules. Androstenone (5α-androst-16-en-3-one) is a volatile steroid best known as the main cause of “boar taint,” the off-putting smell in pork from uncastrated male pigs. Androstenol (5α-androst-16-en-3α-ol) is the alcohol form, often described as having a musky or sandalwood-like smell. Androstadienone (4,16-androstadien-3-one) is found in male sweat and has drawn the most attention in human behavioral research. All three belong to the 16-androstene steroid group and share the same basic carbon framework, but their different functional groups give them distinct odor profiles and biological activities.
These compounds are produced through the same biosynthetic pathway as sex steroids. Research using transformed human kidney cells showed that the enzymes responsible for processing sex hormones can efficiently convert a precursor molecule into androstenol, confirming that androstenol is produced within the sex-steroid biosynthetic pathway rather than being some unrelated metabolic byproduct.1PubMed. Comparative biosynthetic pathway of androstenol and androgens In boars, androstenone is synthesized in the testes, circulates through the bloodstream, and accumulates in fat tissue and salivary glands, where it serves as a sexual signal to sows.2Applied Animal Behaviour Science. A novel boar pheromone mixture induces sow estrus behaviors and reproductive success In humans, androstadienone is secreted in sweat, particularly from the axillary glands under the arms, and androstenone appears in perspiration as well.
Natural Occurrence Beyond Pigs and People
One of the more surprising facts about these compounds is that they turn up in foods. Androstenone has been detected in celery and, more famously, in truffles. Laboratory analysis of truffles found that mature specimens contained measurable levels of α-androstenol along with higher concentrations of related isomeric compounds, while immature truffles had roughly half the amount.3Advanced Materials Research. Study on Extraction and Detection of α-Androstenol in Truffle This finding has fueled a long-standing theory that pigs are so good at finding truffles underground precisely because the fungi produce the same steroid compounds that function as pheromones in pig reproduction. Whether this is the primary reason pigs root for truffles or just a coincidence of chemistry remains debated, but the presence of androstenol in truffles is well established. Androstenone has also been identified in human breast milk, though at trace levels requiring sensitive analytical methods to detect.4PubMed. Development of an analytical approach for identification and quantification of 5-α-androst-16-en-3-one in human milk
Boar Taint and Why the Pork Industry Cares
The single largest commercial concern surrounding androstenone is boar taint, an unpleasant urine-like or sweaty odor and flavor that develops in pork from intact (uncastrated) male pigs. Two compounds are primarily responsible: androstenone and skatole, a bacterial breakdown product from the gut. For decades, the pork industry managed boar taint by surgically castrating male piglets, but welfare concerns have pushed the industry toward alternatives, making accurate measurement and control of these compounds a high priority.
Sensory research shows that androstenone and skatole both contribute to boar taint, but their relative importance depends on what you are measuring. When trained panelists evaluated fat and pork cutlets, odor scores correlated more strongly with androstenone levels than with skatole, and sorting carcasses by androstenone alone was about as effective as sorting by both compounds combined.5Livestock Production Science. Contributions of fat androstenone and skatole to boar taint: I. Sensory attributes of fat and pork meat A more detailed olfactory study, however, found that skatole had a larger effect on overall sensory ratings of fat samples than androstenone did, though both contributed meaningfully, and their combined effect actually weakened at very high concentrations of both.6Journal of Agricultural and Food Chemistry. Interaction of Skatole and Androstenone in the Olfactory Perception of Boar Taint The practical takeaway is that both compounds matter, but androstenone tends to drive the odor complaints that consumers notice most.
To monitor boar taint on slaughter lines, the industry has developed rapid analytical methods. One high-throughput approach using laser desorption and mass spectrometry can quantify androstenone in fat samples down to a limit of 0.10 micrograms per gram, well below the threshold levels used to sort carcasses, with reproducibility tight enough to meet industry standards.7PubMed Central. High throughput method for quantifying androstenone and skatole in adipose tissue from uncastrated male pigs by laser diode thermal desorption-tandem mass spectrometry Wild boars have also been analyzed for taint compounds using similar methods, with researchers measuring androstenone, skatole, and both forms of androstenol in back fat samples.8PubMed. Quantitative determination of the boar taint compounds androstenone, skatole, indole, 3α-androstenol and 3β-androstenol in wild boars (Sus scrofa) reveals extremely low levels of the tryptophan-related degradation products
Immunocastration as an Alternative
One of the most commercially significant alternatives to surgical castration is immunocastration, which uses a vaccine to suppress testicular function temporarily. This approach drastically reduces androstenone accumulation in fat. In a study comparing intact boars to immunocastrated groups vaccinated at different ages, intact boars had average androstenone concentrations in fat around 408 nanograms per gram, while immunocastrated pigs dropped to roughly 62 to 112 nanograms per gram depending on vaccination timing. Skatole levels followed a similar pattern.9PubMed Central. Influences of Immunocastration on Endocrine Parameters, Growth Performance and Carcass Quality, as Well as on Boar Taint and Penile Injuries This strategy lets producers raise intact males for most of their growth period, capturing the feed efficiency and lean-meat advantages of testosterone, then suppress androstenone production before slaughter. It has become the primary welfare-friendly alternative in many markets.
Why Some People Cannot Smell Androstenone
Roughly a third of the adult population cannot smell androstenone at all, a condition called specific anosmia. Among those who can detect it, the experience varies wildly: some people find it foul, like stale urine, while others perceive it as pleasant or woody, and still others report it as nearly odorless. This is not a matter of opinion or attention. It is driven largely by genetics.
A specific odorant receptor gene, OR7D4, plays a central role. Two common genetic variants of this receptor exist, referred to as the RT and WM forms. People who carry two copies of the RT variant tend to be more sensitive to androstenone and rate its smell as more unpleasant. People carrying the WM variant are generally less sensitive and find the odor less objectionable.10PubMed. Genetic variation in a human odorant receptor alters odour perception This genetic variation has practical consequences for food preferences. When people with different OR7D4 genotypes tasted cooked pork containing varying levels of androstenone, those with two copies of the RT variant rated the androstenone-containing meat as less favorable.11PubMed Central. Genetic variation of an odorant receptor OR7D4 and sensory perception of cooked meat containing androstenone In other words, your genes help determine whether you would even notice boar taint in a pork chop.
This variation is not unique to humans. Functional analysis of OR7D4 across primate species revealed an extremely diverse range of receptor responses to these steroid odors, with different primate lineages showing mutations that increase or decrease sensitivity.12PubMed Central. Dynamic functional evolution of an odorant receptor for sex-steroid-derived odors in primates Behavioral testing in three nonhuman primate species found that they responded to both androstenone and androstenol, suggesting these compounds may play a role in olfactory communication across primates. The high rate of specific anosmia in humans, compared to other primates, may reflect the reduced number of functional olfactory receptor genes in our species.13Chemical Senses. Olfactory Responsiveness to Two Odorous Steroids in Three Species of Nonhuman Primates
Training Your Nose to Detect Androstenone
The anosmia to androstenone is not always permanent. Early research demonstrated that systematic repeated exposure could induce the ability to smell androstenone in people who initially could not. In one classic experiment, half of the initially insensitive participants gained the ability to perceive it after regular sniffing sessions.14PubMed Central. Ability to perceive androstenone can be acquired by ostensibly anosmic people More recent work confirmed this at a larger scale. In a study of 335 participants, about 31% were initially anosmic to androstenone. After olfactory training, roughly 72% of those in the training group became able to detect it, with significant improvements in both detection threshold and perceived intensity. Interestingly, the OR7D4 gene variants were not closely linked to how well someone responded to the training, suggesting that the mechanism of acquired sensitivity involves neural plasticity beyond just the receptor itself.15PubMed Central. Olfactory training in specific anosmia to androstenone and its association with genetic variations of OR7D4
This is a genuinely unusual finding. For most odors, you either have the receptor or you do not. The fact that repeated exposure can create sensitivity to androstenone in a large fraction of previously anosmic people suggests something different is happening at the neural level, though exactly what remains under investigation.
Effects on Human Brain Activity, Mood, and Behavior
The androsten compounds have drawn attention for their effects on the human brain, and this is where the science gets both interesting and contested. Brain imaging studies showed that when women smelled an androgen-like compound, it activated the hypothalamus, a brain region involved in hormonal regulation and reproductive behavior, rather than the typical olfactory brain areas. Men did not show the same hypothalamic response to the androgen compound but did when smelling an estrogen-like one.16Neuron. Smelling of Odorous Sex Hormone-like Compounds Causes Sex-Differentiated Hypothalamic Activations in Humans A follow-up study specifically examining androstenol confirmed hypothalamic activation in women, along with activation of the amygdala, a pattern distinct from what ordinary odors produce.17PubMed Central. Androstenol – a Steroid Derived Odor Activates the Hypothalamus in Women
Behavioral experiments have produced a range of suggestive findings. In one study, participants rated photographs of the opposite sex as more attractive after sniffing androstenol compared to a control odor, and this effect did not depend on whether they found androstenol’s smell pleasant. Male participants felt more lively, and both men and women reported feeling more “sexy” when the compound was delivered through the right nostril, though left-nostril exposure was associated with increased irritability.18PubMed. Judgements of attractiveness of the opposite sex and nostril differences in self-rated mood: The effects of androstenol In speed-dating experiments, women exposed to androstadienone rated men as more attractive in two out of three studies.19PubMed. Evidence that androstadienone, a putative human chemosignal, modulates women’s attributions of men’s attractiveness Another experiment found that sniffing androstadienone modulated mood, memory, and autonomic responses such as skin temperature, though these effects emerged mainly during specific behavioral contexts like sexually arousing scenarios.20PubMed. Sniffing human sex-steroid derived compounds modulates mood, memory and autonomic nervous system function in specific behavioral contexts
The Pheromone Debate and the Replication Problem
If you have ever seen androstenone or androstadienone described as “human pheromones” in a perfume ad or a magazine article, you should know that the scientific community has not reached that conclusion. A pheromone, in the strict biological sense, is a chemical signal released by one individual that triggers a reliable, specific response in another member of the same species. Androstenone functions as a genuine pheromone in pigs, where it reliably triggers lordosis (the mating posture) in estrous sows. No equivalent fixed behavioral response has been demonstrated in humans.
A pointed critique published in the Philosophical Transactions of the Royal Society observed that despite no solid evidence that androstadienone or estratetraenol were ever pheromones, nearly 60 studies had claimed significant results from them. The authors argued that many of these findings are likely false positives, exemplifying the broader reproducibility crisis in the life sciences, where small sample sizes and subtle effects create ideal conditions for unreliable results.21PubMed Central. Reproducible research into human chemical communication by cues and pheromones: learning from psychology’s renaissance The studies showing attractiveness boosts and mood changes are real in the sense that they were conducted and analyzed, but few have been independently replicated with adequate power. The field sits in a frustrating middle ground: the neuroimaging evidence for hypothalamic activation is fairly robust, suggesting these compounds are processed differently from ordinary smells, but the behavioral effects remain inconsistent enough that strong claims about human pheromones are premature.
This distinction matters for consumers. Products sold as “pheromone sprays” or “attraction colognes” containing androstenone or androstadienone lean heavily on the marketing appeal of the word pheromone. The concentrations used in commercial fragrances are rarely disclosed, and the leap from “activates the hypothalamus in a brain scanner” to “makes strangers find you irresistible” is enormous and unsupported by reliable evidence.
Commercial Uses in Swine Reproduction
Where androsten compounds genuinely earn their commercial keep is in pig farming, not perfume counters. Boar pheromone products are a well-established tool for managing sow reproduction. Traditionally, farmers walk a live boar through a barn of sows to stimulate estrus detection, the “boar exposure” method that has been standard practice for decades. Commercial pheromone sprays now replicate this effect chemically.
One commercial product, Boar Better, contains a mixture of androstenone, androstenol, and quinoline. In a study of peri-pubertal gilts, self-administration of this spray stimulated estrus at rates comparable to or better than exposure to a live boar. Among gilts old enough to breed, about 93% of those exposed to the pheromone spray showed estrus, compared to roughly 83% of those exposed to a live boar.22PubMed Central. Self-Administration of a Boar Priming Pheromone Stimulates Puberty in Gilts without Boar Exposure Products like these reduce the labor, biosecurity risk, and animal-handling challenges of maintaining breeding boars, and they can be applied by farm workers without specialized training. The active pheromone molecules in these sprays are the same androsten compounds that accumulate in boar saliva and fat naturally.
Androstenol as a Potential Neurosteroid
An emerging area of research looks at androstenol from a completely different angle: its activity in the brain as a modulator of neurotransmitter receptors. Androstenol has been identified as a GABA-A receptor modulator, meaning it can enhance the activity of the brain’s primary inhibitory signaling system. This is the same mechanism exploited by benzodiazepines and some anesthetics. A genomics-based drug repurposing study flagged androstenol as a compound with antiepileptic potential, noting that it showed protective effects in rodent models of seizures.23Oxford Academic (Human Molecular Genetics). Identifying new antiepileptic drugs through genomics-based drug repurposing This line of investigation is still early-stage, with no human clinical trials to point to, but it represents a striking expansion of the androsten story. A compound primarily known for making pork smell bad and possibly influencing human mood turns out to interact with a major neurological system in ways that could, in principle, be medically useful.
The broader class of neurosteroids, steroids that modulate brain activity rather than acting through traditional hormonal pathways, has produced at least one FDA-approved drug for postpartum depression. Androstenol’s placement within this class is still being explored, and it would be premature to call it a drug candidate. But the fact that a steroid derived from the sex-hormone pathway can double as a brain inhibitor underscores how versatile the androstane skeleton is as a chemical scaffold.
Measurement Challenges and Why Precision Matters
One underappreciated aspect of androsten research is how difficult these compounds are to measure accurately, and how much depends on getting the measurement right. In the pork industry, the sorting threshold for androstenone in fat, the level above which a carcass is likely to produce objectionable odor, is a commercial decision with direct financial consequences. Set it too low and you reject too many carcasses. Set it too high and you allow tainted meat through. The analytical methods used need to be both sensitive enough to catch low levels and fast enough for use on slaughter lines handling thousands of animals per day.7PubMed Central. High throughput method for quantifying androstenone and skatole in adipose tissue from uncastrated male pigs by laser diode thermal desorption-tandem mass spectrometry
In human research, measurement challenges are even steeper. The concentrations of androstenone in sweat are tiny, and controlling for confounding odors in behavioral experiments requires careful experimental design. Many of the earlier studies criticized for poor replicability used imprecise delivery methods and did not adequately control for participants’ varying genetic sensitivity. The finding that roughly a third of participants cannot smell androstenone at all means that any study failing to genotype or screen its participants is effectively mixing responders and non-responders in the same analysis, diluting whatever effect might exist.15PubMed Central. Olfactory training in specific anosmia to androstenone and its association with genetic variations of OR7D4 Future studies that pre-screen for OR7D4 genotype and anosmia status before testing behavioral effects are more likely to produce reliable findings, though such studies are more expensive and harder to recruit for.