Why Is Pubic Hair So Curly? The Science Explained

Pubic hair gets its tight curl from the shape of the follicle it grows out of and the lopsided internal structure of the hair shaft itself. Unlike many scalp follicles, which sit relatively straight in the skin, pubic hair follicles are curved and produce strands with an uneven distribution of structural proteins, forcing the hair to coil as it emerges. The story is more involved than “it’s just a different kind of hair,” though, because the hormones that trigger pubic hair growth, the physical properties of the strands, and even the microbial communities living on them all differ from what you find on your head.

The Follicle Is Bent Before the Hair Even Grows

Hair curl starts underground. The follicle, which is the tiny tube in the skin that produces a hair strand, has a shape that predetermines whether the emerging fiber will be straight or curly. Research on curly scalp hair has shown that follicles producing tightly curled hair are physically curved beneath the skin, with a distinctive bend at the base (the bulb) that researchers have compared to the hook of a golf club. Inside that bent bulb, the cells that divide to build the hair strand don’t divide evenly on all sides. Proliferating cells cluster more heavily on the convex (outer curve) side and extend higher up than they do on the concave side, creating an asymmetry in how the hair is assembled from the very start.¹

Pubic follicles share this curved architecture. Because the follicle itself is hooked, the hair shaft is forced into a curved path as it’s pushed upward by new cell growth. Think of it like pushing toothpaste through a bent nozzle: what comes out curves because the channel it’s traveling through curves. The tighter the bend in the follicle, the tighter the resulting curl. Pubic follicles tend to have sharper curvature than most scalp follicles, which is one reason pubic hair is typically curlier than the hair on your head, even if your scalp hair is already wavy or curly.

Lopsided Proteins Inside the Hair Shaft

The follicle shape isn’t the whole explanation. The hair strand itself has an internal structure that reinforces the curl. Hair is made mostly of keratin, a tough structural protein, organized into bundles called intermediate filaments that run the length of the fiber. In curly hair, these filaments aren’t arranged the same way on all sides of the strand.

Studies using X-ray scattering to peer inside individual hair fibers found that, regardless of a person’s ethnic background, curly hairs contain two distinct types of cortex cells arranged on opposite sides of the strand. The type of cortex on the convex side (the outside of the curl) contains discrete bundles of filaments arranged in helical patterns, while the cortex on the concave side (the inside of the curl) has larger, fused bundles with filaments packed in more parallel, hexagonal arrays.² This bilateral arrangement, with one cortex type on each side, creates a structural imbalance. The two sides swell, contract, and respond to moisture differently, which bends the fiber into a curve. The more pronounced the asymmetry, the tighter the curl.

This finding holds across populations. Researchers comparing hair from people of African, Caucasian, and Asian descent concluded that the macroscopic curl of any hair fiber originates from this inhomogeneous distribution of the two cortex types, not from surface texture or cross-sectional shape alone.³ A specific keratin protein, hHa8, has been shown to accumulate on the concave side of curly hair strands while distributing evenly in straight ones, further confirming that the curl is “baked in” at a molecular level.⁴

Pubic hair tends to have an elliptical cross-section rather than a perfectly round one, and its shaft and medulla diameters are larger than those of scalp or underarm hair.⁵ That elliptical shape compounds the asymmetry: a rounder cross-section allows more even protein distribution, while an oval one almost guarantees that different cortex types will land on opposite sides. The result is a fiber that’s structurally predisposed to curl tightly.

Androgens Flip the Switch at Puberty

You don’t have curly pubic hair as a small child because pubic hair doesn’t exist yet, at least not in its adult form. Before puberty, the groin is covered in vellus hair: the fine, nearly invisible fuzz that blankets most of your body. At puberty, rising levels of androgens, primarily testosterone and its more potent derivative, transform those tiny vellus follicles into much larger terminal follicles capable of producing thick, pigmented, curly hair.⁶ The same hormonal signal triggers terminal hair in the armpits and, in men, on the face, chest, and back.

Historical evidence underscores just how dependent this process is on androgens. Boys who were castrated before puberty (eunuchs) never developed terminal pubic hair at all. Those castrated after puberty experienced a gradual thinning of pubic hair density, though it didn’t disappear completely, since the follicles had already been permanently reprogrammed.⁷ The transformation is more dramatic in men than in women on average, but both sexes undergo the same fundamental vellus-to-terminal shift in the pubic and axillary regions.

What androgens actually do to the follicle at a structural level isn’t fully mapped, but the outcome is clear: the newly enlarged follicle develops the curved architecture and asymmetric protein distribution described above. The follicle essentially rebuilds itself into a curl-producing machine during adolescence, and it stays that way for life.

Genetic Roots of Curl

If follicle curvature and protein distribution determine how tightly hair curls, the obvious question is what determines follicle curvature and protein distribution. The answer, so far as researchers have gotten, is genetics, though the specific genes are only beginning to be identified.

A genome-wide study comparing people with low and high curl found strong links to variation in trichohyalin (a protein involved in hardening the inner root sheath of the follicle), a copper transporter protein called CUTC, and keratin 74, a component of the inner root sheath.⁸ These findings point to the inner root sheath, the sleeve that wraps around the developing hair fiber inside the follicle, as a key player. If the sheath hardens unevenly or shapes the fiber asymmetrically, the resulting strand comes out curled.

Those genetic associations were identified for scalp hair, and no equivalent genome-wide study has been published specifically for pubic hair curl. But because the same basic follicle biology governs hair at all body sites, the same or closely related genes likely influence pubic hair curliness. The added wrinkle is that pubic follicles are also responding to local androgen signaling, so the genetics of androgen receptor sensitivity and local enzyme activity layer on top of the structural genes. The research is still catching up. Hair genetics has historically focused on scalp hair for obvious commercial reasons, leaving body-site-specific questions largely unexplored.

What the Curl Is Good For

People often assume pubic hair is an evolutionary leftover with no real function, but there are several plausible reasons why humans retained thick, curly hair in the groin long after losing most of their body hair. None of these are definitively proven as “the” evolutionary reason, since evolutionary-purpose arguments are inherently hard to test, but the evidence supporting them is more than anecdotal.

The most straightforward function is physical protection. The groin has thin, sensitive skin that rubs against itself and against clothing constantly. A dense mat of curly hair creates a cushion that reduces friction and helps prevent chafing during movement and intercourse. Curly hair is better at this than straight hair would be because the coils interlock and create a springy, three-dimensional buffer rather than lying flat against the skin.

Curly pubic hair also traps air between its coils, which helps regulate moisture and temperature in a region that tends to be warm and damp. This meshes with microbiome research showing that the bacterial communities on pubic hair closely resemble those of the surrounding groin skin, which favors moisture-loving bacteria. The hair creates and maintains a specific microenvironment.⁹

A less-discussed function involves scent dispersal. The groin contains apocrine sweat glands, the same type found in the armpits, which produce the oily secretions that bacteria break down into body odor. Curly hair dramatically increases the surface area available to hold and gradually release these volatile compounds. In many mammals, body odor plays a role in sexual signaling, and while modern humans tend to suppress these scents, the anatomical setup for pheromone-like communication is still intact.

Pubic Hair as a Touch Sensor

Hair follicles aren’t just structural. They’re wired into your nervous system and act as sensitive mechanoreceptors, detecting light touch, pressure changes, and even air movement. Sensory neurons wrap around each follicle, and when the hair shaft is deflected, those neurons fire. Recent research has added a layer to this picture: the outer root sheath cells of the follicle itself actively release signaling molecules, including serotonin, histamine, and ATP, when they’re mechanically stimulated. These molecules then activate the surrounding sensory neurons.¹⁰

In other words, hair follicles don’t just passively transmit touch. They amplify it chemically. In the genital region, where nerve density is already high and sensory input is closely tied to sexual function, this amplification effect could be particularly relevant. Curly hair, with its springy, interlocking structure, may transmit different patterns of mechanical stimulation compared to straight hair, potentially enhancing tactile sensitivity. The research didn’t test this body-site-specific angle directly, but the basic mechanism, outer root sheath cells acting as signal boosters, applies to follicles across the body.

A Distinct Microbial World

The bacterial community living on your pubic hair is measurably different from the one on your scalp hair, and the difference isn’t random. Pubic hair is dominated by Corynebacterium, which made up about 40% of the identified bacteria in one study, compared to only 7% on scalp hair. Scalp hair, by contrast, carries more Staphylococcus and a higher proportion of uncultured bacteria. Corynebacterium prefers the moist conditions of the groin, and researchers found that the microbial communities on hair shafts closely mirror those of the adjacent skin at each body site.¹¹

This means pubic hair isn’t just passively sitting there; it’s hosting and maintaining a microbial ecosystem shaped by the local environment. The curl of the hair likely contributes to this by increasing surface area and trapping the moisture and sebum these bacteria feed on. Whether this microbiome actively protects against pathogenic bacteria (as some researchers hypothesize) or simply reflects the local conditions is an open question, but the hair clearly plays a role in shaping what grows there.

What Changes When You Remove It

Given that pubic hair appears to serve protective and ecological functions, it’s worth looking at what happens when people remove it. Pubic grooming is extremely common, and research into its consequences has grown considerably in the past decade.

A study of women found that about 60% of those who groomed had experienced at least one health complication, with the most common being epidermal abrasion and ingrown hairs.¹² Ingrown hairs are especially common with curly pubic hair because the tightly coiled shaft can curve back into the skin after being cut or shaved, triggering inflammation. Straight hair is less prone to this because it tends to grow away from the skin surface rather than curling back toward it. If you’ve ever wondered why bikini-line razor bumps are worse than leg razor bumps, the follicle curvature is a big part of the answer.

The relationship between pubic grooming and sexually transmitted infections has gotten considerable attention but remains contested. A large nationally representative study found that people who groomed were roughly twice as likely to report a history of STIs compared to non-groomers, even after adjusting for age and number of sexual partners. The association was strongest for skin-to-skin infections and was more pronounced among people who groomed frequently or extensively.¹³ A systematic review and meta-analysis found that groomers had higher odds of gonorrheal and chlamydial infections specifically, though no significant difference for viral infections like herpes or genital warts.¹⁴

Not all studies agree, though. A study of female university students found no evidence of a link between extreme pubic grooming and gonorrhea or chlamydia infection.¹⁵ The discrepancy may come down to study design: the larger nationally representative study relied on self-reported STI history, while the university study used actual lab-confirmed infections in a narrower population. Confounding factors are also hard to rule out, since people who groom extensively may differ from non-groomers in sexual behavior in ways that surveys don’t fully capture.

The plausible biological mechanism connecting grooming to infection risk involves micro-abrasions. Shaving or waxing creates tiny breaks in the skin that could serve as entry points for bacteria and viruses. Removing the hair also eliminates the physical barrier and the moisture-regulating microenvironment the hair provides. Whether this translates into a meaningful increase in real-world infection risk for any given person is still unclear, but the pattern across multiple studies is consistent enough to be worth noting.

Why Pubic Hair Behaves Differently from Scalp Hair

People sometimes wonder why their scalp hair can be straight while their pubic hair is tightly curled, or why the two textures seem so unrelated. The answer is that follicles at different body sites are subject to different local signals. Pubic follicles undergo androgen-driven transformation at puberty that scalp follicles don’t, they sit in skin with different thickness and tension, and they produce hair with different shaft dimensions. Pubic hair strands are thicker in both shaft and medulla diameter than scalp hair, and they tend to be more elliptical in cross-section.⁵ That combination of wider shaft, more oval shape, and more pronounced follicle curvature means pubic hair curls tighter than scalp hair in virtually everyone, even people whose scalp hair is very curly.

Pubic hair also has a shorter growth cycle than scalp hair. While a scalp hair can grow for several years before falling out, pubic hair reaches terminal length in a matter of months. This is why pubic hair stays relatively short compared to head hair, regardless of whether you trim it. The shorter growth phase, combined with the tight curl, gives pubic hair its characteristic dense, compact appearance rather than the flowing length you see on the scalp.

The differences extend to the surface of the strand as well. The microbial communities on pubic hair are adapted to the warm, moist, enclosed environment of the groin, with a bacterial profile distinct from that on the scalp.¹¹ Everything about pubic hair, from its molecular structure to its resident bacteria, reflects its specific body-site niche. It may look like a minor variation on head hair, but biologically it’s a substantially different system shaped by different forces.