Coarse hair is primarily determined by genetics, which set the diameter of your hair shaft. A coarse strand measures 80 microns or more in diameter, compared to fine hair at under 60 microns. But genetics aren’t the only factor. Hormones, aging, medications, and certain medical conditions can all shift your hair texture from fine or medium toward coarse over time.
How Hair Diameter Is Set
The thickness of each hair strand is controlled by the dermal papilla, a small cluster of cells at the base of the follicle. The size of the dermal papilla directly determines the size of the hair it produces: a larger papilla creates a thicker strand. Your genes dictate how large these papillae are across your scalp and body, which is why hair texture tends to run in families. Ethnicity plays a role too. East Asian hair, for instance, tends to have the widest individual strand diameter, while European and African hair types vary more widely.
It’s worth noting that coarse hair and thick hair aren’t the same thing. Coarse refers to the width of individual strands. Thick refers to density, meaning how many strands grow per square centimeter of scalp. You can have coarse hair that’s thin (wide strands, but fewer of them) or fine hair that’s thick (narrow strands packed closely together).
Hormones and Puberty
The most dramatic shift toward coarse hair happens during puberty, when rising androgen levels transform hair follicles across the body. Before puberty, much of your body is covered in vellus hair: tiny, pale, almost invisible strands. Androgens like testosterone signal vellus follicles to become terminal follicles, which produce larger, pigmented, coarser hairs. This is why armpit hair, facial hair, and pubic hair appear during adolescence.
The mechanism works through the dermal papilla. Androgens from the bloodstream bind to receptors inside dermal papilla cells, which then change the growth signals they send to surrounding cells. These altered signals cause the follicle to enlarge, the hair shaft to widen, and melanocytes to produce more pigment. The result is a visibly thicker, darker strand replacing what was once peach fuzz.
Different body sites respond to androgens in completely different ways, even within the same person. Beard follicles convert testosterone into a more potent form called DHT, which drives the coarsening effect. Armpit and pubic follicles respond to testosterone directly, without that conversion step. Meanwhile, scalp follicles in people prone to pattern baldness actually shrink in response to the same hormones. This paradox explains why someone can simultaneously grow a thicker beard and lose hair on top of their head.
Medical Conditions That Change Hair Texture
Certain hormonal disorders can trigger unexpected coarsening of hair, particularly in women. Polycystic ovary syndrome (PCOS) is one of the most common causes. Elevated androgen levels stimulate terminal hair growth on the face, chest, and abdomen, a pattern called hirsutism. The hair in these areas becomes noticeably thicker and darker than what was there before.
Cushing’s syndrome, a condition caused by prolonged exposure to high cortisol levels, produces a similar effect. Women with Cushing’s syndrome may develop thick, dark hair on the face and body. Thyroid disorders can also alter hair texture. An underactive thyroid sometimes makes hair feel dry and coarse, while an overactive thyroid can change the texture in the opposite direction, making it finer and more fragile.
Why Gray Hair Feels Coarser
If you’ve noticed that your gray hairs have a distinctly wiry, rough texture compared to your pigmented strands, you’re not imagining it. Inside the follicle, melanocyte stem cells (which produce pigment), keratinocyte activity, and sebaceous gland secretions all work together to determine both color and texture. As you age, the activity of these systems declines. You lose not just pigment but also lipids and growth factors that kept the strand smooth and pliable.
The result is hair that’s structurally different. Gray strands tend to have a rougher cuticle surface, making them feel stiffer and harder to manage even if the actual diameter hasn’t changed much. Reduced sebum production from the oil glands attached to each follicle compounds the problem, leaving gray hair drier and more resistant to styling.
Medications That Alter Hair Texture
Several categories of medication can change hair texture as a side effect. A review in the Journal of Drugs in Dermatology identified texture changes most commonly with cancer drugs (97 cases), anti-seizure medications (56 cases), retinoids used for skin conditions (15 cases), and immunomodulators (3 cases). The changes most often involve hair growing back curlier, kinkier, or wavier than before, a phenomenon cancer patients have nicknamed “chemo curl.”
These shifts happen because the drugs disrupt the normal growth cycle of the follicle or alter the shape of the hair shaft as it forms. With some medications, the change reverses after stopping treatment. But with retinoids, certain cancer drugs, and antiretroviral therapy, the texture changes were linked to irreversible alterations in the follicle. If you’ve noticed your hair texture changing after starting a new medication, the drug itself is a plausible explanation.
Nutrition and Hair Health
While genetics and hormones are the primary drivers of coarse hair, nutritional status plays a supporting role. Iron, zinc, biotin, and protein are all essential building blocks for keratin, the protein that makes up the hair shaft. Deficiencies in these nutrients don’t typically make hair coarser, but they can change its texture in other ways, making it brittle, dry, or rough to the touch. Adequate hydration and healthy fat intake support the sebaceous glands that keep hair smooth, so a diet very low in fat can leave hair feeling coarser than usual even if the strand diameter hasn’t changed.
Coarse Hair by Birth vs. Coarse Hair That Develops
If your hair has always been coarse, the cause is almost certainly genetic. Your follicles are simply built to produce wide-diameter strands, and there’s nothing abnormal about that. Coarse hair is often stronger and more resistant to damage than fine hair, even if it can be harder to style.
If your hair has become coarser over time, the cause depends on your circumstances. Puberty and pregnancy involve normal hormonal shifts that commonly thicken hair. Aging changes texture through reduced oil production and cuticle changes. A sudden or unexplained shift toward coarser, darker hair, especially in unusual locations, points toward a hormonal imbalance worth investigating. And if the change coincides with a new medication, that connection is worth raising with your prescriber.