Apocrine Sweat Glands: Location, Function, and Body Odor

Apocrine sweat glands are the larger, less numerous type of sweat gland in the human body, concentrated in the armpits, groin, and around the nipples. Unlike the eccrine glands that cover most of your skin and regulate temperature, apocrine glands produce an oily, protein-rich secretion that is initially odorless but becomes the primary source of body odor once bacteria get to work on it. These glands sit dormant through childhood and switch on at puberty under the influence of sex hormones, which is why body odor becomes a new reality for teenagers.

Where Apocrine Glands Are and How They Differ From Eccrine Glands

Your body has two main populations of sweat glands. Eccrine glands number in the millions, covering nearly every square centimeter of skin, and they produce the thin, watery sweat that cools you down during exercise or on a hot day. Apocrine glands are far more restricted in their real estate. They cluster in the axillary region (armpits), the perineal and perianal area, the genitals, and the tissue surrounding the nipples.¹ A few are scattered in the scalp and on the eyelids (the glands of Moll), but for practical purposes the armpit is the apocrine epicenter that matters most for daily life.

Structurally, apocrine glands are larger and sit deeper in the skin than eccrine glands. Each one is a coiled, branched tube nestled in the lower dermis or subcutaneous fat, and its duct empties into a hair follicle rather than directly onto the skin surface. This follicular connection is important: it means apocrine secretion mingles with sebum and hair before reaching the outside world, creating a richer chemical environment for the skin bacteria that generate odor.

There is also a third, lesser-known type called the apoeccrine gland, which shares features of both. Apoeccrine glands develop during puberty in the axillary region and drain directly onto the skin surface rather than into a hair follicle. They produce a more watery secretion than true apocrine glands, and their clinical relevance has come up in research on conditions like Fox-Fordyce disease, where blockage of their ducts can trigger itchy bumps.²

Why They Stay Silent Until Puberty

Apocrine glands are present from birth, but they do not begin secreting until puberty. The trigger is sex hormones. The secretory lining of apocrine glands contains androgen receptors and estrogen receptors, and research on axillary glands has found strong receptor expression in the taller, more active segments of the gland lining, suggesting a direct link between hormone binding and secretory output.³ Androgen receptors have also been identified in the luminal cells of apocrine glands in genital skin.⁴

Androgens are known to ramp up cholesterol production in cells, and cholesterol serves as a raw material for some of the volatile compounds in apocrine secretion. This is one proposed pathway through which hormonal changes at puberty lead to body odor: rising androgen levels activate the glands, the glands produce cholesterol-derived precursors, and skin bacteria convert those precursors into smelly byproducts.⁵ Emotional stress, adrenaline, and sexual arousal also provoke apocrine secretion, though the mechanism is not a direct nerve signal. Research has found no nerve fibers near apocrine glands themselves, indicating that stimulation happens through circulating hormones and neurotransmitters reaching the glands via the bloodstream.⁶

What Apocrine Glands Actually Produce

Fresh apocrine secretion is a milky, viscous fluid with no significant smell on its own. It is chemically very different from the dilute saltwater that eccrine glands produce. Lipid profiling of apocrine sweat has identified around 240 distinct lipid molecules across 15 different classes. Ceramides made up the single most diverse class, while free fatty acids were the most concentrated, reaching levels roughly ten thousand times higher than the rarest lipid species detected.⁷ The secretion also contains proteins, steroids, and ammonia. It is this chemical richness that makes apocrine sweat such an attractive food source for bacteria.

The glands release their contents through a process sometimes called “decapitation secretion,” in which the top of the secretory cell pinches off and releases a blob of cytoplasm into the gland lumen. This is different from eccrine glands, which secrete fluid through membrane channels without losing cell material. The result is that apocrine secretion carries cellular debris, lipid droplets, and pigment granules along with it.

How Bacteria Turn Apocrine Sweat Into Body Odor

Body odor is not really about sweat; it is about what microbes do with sweat. The armpit is a warm, moist habitat packed with bacteria, and apocrine secretion delivers a buffet of fats, proteins, and amino acids for them to metabolize. The primary culprits include species of Corynebacterium and Staphylococcus. In one study, five bacterial strains isolated from underarm sweat, including Corynebacterium tuberculostearicum, Staphylococcus epidermidis, and Bacillus licheniformis, all produced strong odors when incubated with sterile sweat collected from male volunteers.⁸

The specific smell depends on which bacterial species dominate and which metabolic pathways they favor. Research on underarm microbiomes has shown that S. epidermidis produces both acetic acid (vinegar-like sour odor) and isovaleric acid (the cheesy, sweaty-feet smell) through the breakdown of amino acids like leucine and valine.⁹ Corynebacterium species, meanwhile, are especially efficient at converting odorless precursors in apocrine sweat into thiol compounds, which are responsible for the pungent, onion-like component of armpit odor. The molecule 3-methyl-3-sulfanylhexan-1-ol has been identified as a major contributor to the characteristic human axillary smell.¹⁰

This is why body odor does not emerge until puberty even though skin bacteria are present from infancy: the bacteria need the apocrine precursors that only become available once the glands switch on. Children have armpit bacteria but lack the substrate, so the microbial community cannot produce the volatile compounds associated with adult body odor.

The Gene That Links Earwax Type and Body Odor

One of the more surprising findings in apocrine gland biology is that a single gene variant determines both your earwax type and how much you smell. The gene is called ABCC11, and it codes for a transporter protein that moves molecules across cell membranes, including into the lumen of apocrine glands. A single change in this gene (known as 538G>A) has two versions: the G allele produces wet, sticky earwax and active apocrine secretion, while the A allele produces dry, flaky earwax and much less apocrine output.¹¹

People who carry two copies of the A allele (the dry-earwax genotype) produce substantially less apocrine secretion and, consequently, much less body odor. This genotype is rare in people of European and African descent but extremely common in East Asian populations, where it has reached frequencies above 95% in some groups.¹² This explains why deodorant use has historically been less culturally emphasized in parts of East Asia compared to Western countries: a large majority of the population simply does not produce the apocrine precursors that bacteria need to generate strong body odor.

The clinical link is striking. In a study of Japanese patients diagnosed with axillary osmidrosis (the medical term for pathologically strong body odor), nearly 99% carried at least one copy of the wet-earwax G allele, compared to about 35% of the general Japanese population.¹³ If you have dry earwax, you almost certainly do not have a clinical body odor problem. If you have wet earwax, you have the biological hardware for it, though personal hygiene and bacterial community composition still matter.

Conditions Involving Apocrine Glands

Several skin conditions center on or involve apocrine glands, ranging from mildly annoying to painful and chronic.

Bromhidrosis and Chromhidrosis

Bromhidrosis is the clinical term for abnormally foul-smelling sweat. It typically arises when excessive apocrine (or sometimes eccrine) secretion is broken down by skin bacteria, and the condition can be worsened by factors like obesity, diabetes, or skin infections that promote bacterial overgrowth.¹⁴ The axillary sweat glands themselves are considered the central factor, though hormones, genetics, and the individual’s microbial community all contribute.¹⁵

Chromhidrosis is rarer and more visually dramatic: the glands produce colored sweat, usually yellow, green, blue, or black. In the apocrine form, the color comes from lipofuscin pigment granules that accumulate in the secretory cells.¹⁶ People with this condition may notice colored stains on clothing, particularly in the underarm area. It is harmless but understandably distressing, and diagnosis typically requires a biopsy showing the characteristic pigment granules in apocrine tissue.

Hidradenitis Suppurativa

Hidradenitis suppurativa (HS) is a chronic, painful inflammatory condition that produces abscesses, draining tunnels, and scarring in apocrine-bearing skin, particularly the armpits and groin. For decades, the dominant theory held that HS begins with plugging of hair follicles rather than a primary problem in the apocrine glands, and studies have found that follicular blockage by keratinous material, followed by folliculitis and secondary destruction of surrounding structures, is a core part of the disease process.¹⁷

However, more recent work has reopened the question. A 2024 study using tissue samples from HS patients found that apocrine glands showed destruction and significant shrinkage even in skin that had not yet developed visible lesions. Damaged apocrine cells released specific keratins (keratin 18 and keratin 19) that appeared to recruit immune cells, particularly neutrophils, suggesting the glands may be involved earlier in the disease than previously believed.¹⁸ The exact sequence, whether follicular plugging injures the glands or whether gland damage contributes independently to the inflammation, is still being sorted out.

Treating Apocrine-Related Odor Problems

For people whose body odor goes beyond what regular hygiene and commercial deodorants can manage, there are medical and surgical options that target apocrine glands directly.

Botulinum toxin injections (the same drug used cosmetically under various brand names) have proven effective for axillary bromhidrosis. In a prospective trial comparing treated and untreated armpits in the same patients, the treated side showed a dramatic drop in both odor intensity and sweat production at three months. Under the microscope, the apocrine glands in the treated skin appeared shrunken and underdeveloped, suggesting the toxin does not merely block nerve signals but may cause the glands themselves to atrophy temporarily.¹⁹ The effect is not permanent; in one series of 53 patients who had already undergone prior surgery, botulinum toxin provided relief lasting a median of about six months, and the vast majority rated their satisfaction as good or very good.²⁰

Surgical removal of apocrine glands is the more definitive approach. Traditional techniques involve making a small incision and scraping or trimming the gland-bearing tissue from the underside of the skin. Newer methods have improved outcomes. A technique using a nasal endoscope with a suction cutter achieved a 100% combined effectiveness rate in a series of 98 patients, compared to about 89% for the older small-cut trimming method, with fewer complications as well.²¹ Even after surgical removal, some odor can recur if gland tissue is not completely excised or if remaining eccrine glands contribute to the problem, which is where follow-up botulinum toxin injections can fill the gap.

Evolutionary Origins and the Mammary Gland Connection

Apocrine glands are evolutionarily ancient. In most mammals, apocrine glands are the dominant sweat gland type and serve primarily as scent glands rather than cooling organs. Humans are unusual in that we have shifted the thermoregulatory burden almost entirely to eccrine glands, a change that likely accompanied the loss of dense body hair and the move into hot, open environments. Research comparing sweat gland traits across primates has found strong evidence of natural selection for increased eccrine sweating capacity in species living in hot, dry climates.²² Humans represent an extreme along this continuum: high eccrine density for cooling, with apocrine glands reduced to a few signaling outposts.

Among other mammals, the Equidae family (horses, zebras, donkeys) is one of the few groups that, like humans, use sweating for thermoregulation. But horses sweat through apocrine-type glands rather than eccrine glands, and their sweat contains a surfactant protein called latherin that helps it spread through a waterproof coat to evaporate.²³ Sweating across mammalian species serves a range of functions beyond cooling, including pheromone delivery and maintenance of the skin’s microbial ecosystem.²⁴

Perhaps the most remarkable evolutionary footnote is that the mammary gland appears to have evolved from an ancestral apocrine-like gland associated with hair follicles.²⁵ The structural parallels are real: both gland types are associated with hair follicles, both use a secretory mechanism that involves releasing cellular material into the lumen, and both produce lipid-rich secretions. The leading hypothesis is that early proto-mammary glands in synapsid ancestors secreted moisture and antimicrobial substances onto eggs or hatchlings, and that this secretion was gradually enriched with fats and proteins over millions of years until it became milk. Your armpit glands and mammary glands, in other words, share a deep common ancestor.

Apocrine Gland Cancers

Cancers arising from apocrine sweat glands are extremely rare but do occur. Primary cutaneous apocrine carcinoma typically presents as a slow-growing nodule in an apocrine-rich area, most commonly the axilla. Because the armpit is also a common site for lymph node metastases from breast cancer, a major diagnostic challenge is ruling out metastatic breast cancer that has spread to the skin. Pathologists rely on a combination of tissue architecture and specialized staining to make the distinction: apocrine carcinomas show characteristic “decapitation secretion” under the microscope and tend to stain positive for certain keratins while staining negative for markers that would suggest breast origin.²⁶

Diagnosis requires both clinical context and immunohistochemistry. Tumors typically express markers like cytokeratin 7 and epithelial membrane antigen, while testing negative for prostate-specific antigen and cytokeratin 20, a pattern that helps distinguish them from metastatic cancers originating elsewhere.²⁷ Because these tumors are so uncommon, there are no large randomized trials guiding treatment. Wide surgical excision is the standard first-line approach, with decisions about radiation or chemotherapy made on a case-by-case basis.²⁸ For most people, the practical takeaway is simply that a new, growing lump in the armpit or groin warrants medical evaluation, though the odds of it being an apocrine carcinoma specifically are vanishingly small.