Having body hair is a normal part of, well, being human. The fine fuzz that covers your skin is made up of vellus hairs (from the Latin word for "fleece"). But those long, coarse, pigmented bad boys? They're called terminal hairs, which make up your eyebrows and eyelashes, and pop up on the scalp, chin, under your arms, and in your pubic area.

The amount of thicker hair that you have on your body usually depends on your genes, says Gary Goldenberg, M.D., an assistant clinical professor of dermatology at the Icahn School of Medicine at Mount Sinai in New York City. "There is a variety of normal: Some will notice very little body hair that's very light in color or texture, whereas others may have more body hair and it may be darker and coarser."

But when your body hair changes suddenly, it can be a tip-off that something isn't quite right elsewhere. Whether it's growing faster than usual, coming in thicker, or even falling out, here are a few things your body hair may be signaling about your health.

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1. Your male hormones are out of balance.

    A sudden increase in hair growth or loss in women is often caused by an imbalance of male hormones (androgens) which are naturally present in both men and women in differing amounts. If you get a boost in testosterone, for example, excess hair can be the result.

    "It's called hirsutism—a condition of unwanted male-pattern hair growth in women," says Margaret E. Wierman, M.D., professor of medicine at the University of Colorado Medical Center in Denver and chief of endocrinology at the Denver Veterans Administration Medical Center. "The 'male-pattern' part of the diagnosis means hair above the belly button, on the upper chest, or on the upper back. More than eight hairs around a single nipple is considered abnormal in women and would meet the definition of hirsutism."

    Much like male-pattern excess hair, male pattern baldness in women is also a sign of shifting male hormone levels. When estrogen levels decline during menopause and, as a consequence, testosterone rises, many women find that the hair on their heads thins while their facial hair becomes coarser. You might even find an errant hair on your chin. "Initially horrifying, yes," says Dr. Wierman, "but all perfectly normal."

    2. It could be a sign of PCOS.

    Polycystic ovary syndrome (PCOS) is a condition caused by an imbalance of reproductive hormones, and affects nearly 1 in 10 women of childbearing age, according to the U.S. Office on Women's Health (OWS).

    That can cause issues in your ovaries, which produce the egg that's released each month as part of your menstrual cycle. With PCOS, this egg might have developmental problems or not be released during your period as it normally would.

    That can spur a slew of symptoms, like irregular periods, adult acne, thinning hair, or too much hair on the face, chin, or other parts of your body. This happens due to increased production of testosterone in your body, Dr. Goldenberg explains, which stimulates excessive body hair growth.

    3. An iron deficiency may be present.

    Everyone has a hair cycle. Some people tend to naturally shed hair in the spring and fall; others in the summer and winter. But diffuse hair loss—noticeable hair loss on your body and your head—can indicate anemia, or a deficiency of iron in your blood. Vegans and vegetarians or women with heavy periods are at a higher risk, and it may result in hair loss, brittle nails, and odd cravings. If you suspect iron may be an issue, see your doctor for a blood test.

    4. An underactive thyroid could be causing problems.

    Your thyroid is a small, butterfly-shaped gland in the front of your neck, and it secretes hormones that help control the way your body uses energy, per the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). When you don't have enough thyroid hormones, many of your body's functions slow down—including how much hair you make.

    Thyroid-related hair loss has specific symptoms, says Dr Wierman: "If you find that you're losing the outside third of your eyebrows and you're developing ridges in your nails, you probably have autoimmune thyroid disease," she says. "Go in for a blood test to have your TSH—or, thyroid-stimulating hormone—levels checked."

    5. Your estrogen levels recently changed.

    The amount of estrogen in your body can also impact your hair. When estrogen levels are high, hair tends to be thicker than usual; When they're low, it can cause hair loss, says Joshua Zeichner, M.D., director of cosmetic and clinical research in dermatology at Mount Sinai Hospital in New York City. A sudden change in your estrogen levels—after pregnancy or stopping birth control pills, for example—can also lead to temporary hair shedding.

    6. Your medication may have side effects.

    Certain medications can have a direct impact on your body hair, Dr. Goldenberg says. Some, including certain antidepressants and anti-coagulants, can cause temporary hair loss, usually through a process called telogen effluvium, a hair shedding condition that can also happen after pregnancy, major surgery, drastic weight loss, or extreme stress.

    Other meds can cause hair growth, including a boost in body hair. Those include testosterone, danazol (also an androgen), phenytoin (an anticonvulsant), and glucocorticoids (a type of steroid), he says. In most cases, the hair changes are not permanent and will end once you stop using the medication.

    7. You could have an autoimmune problem.

    It's rare, but with certain autoimmune conditions, your immune system can go haywire and attack your hair follicles. The result can be losing your hair in odd, circular patches (called alopecia areata); losing all your hair on your scalp (alopecia totalis); or losing all your hair on your head and body, including your eyebrows and eyelashes (alopecia universalis). These conditions are typically treated with systemic steroids, and the hair can grow back—though the cure doesn't always last.

    8. In rare cases, you might have a tumor.

    If hirsutism comes on very suddenly and dramatically—"Say, over a period of six months," says Dr. Wierman—and your testosterone levels and DHEAS levels (a blood test will reveal both) are very high, you may have a tumor that is releasing male hormones and changing the hormone profile in your body to such as extent that you're growing hair and fast.

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    "In these cases, we look for a tumor of the adrenal gland or ovary—both are possibilities," she says. "It's not common, but it's something your doctor will check out."

    ❗When to see your doctor about your body hair

    While having body hair changes can indicate an underlying health issue, it doesn't always mean that something is off. "Most patients that I see with excessive facial or body hair are a variant of normal," Dr. Goldenberg says.

    However, "if you are developing new, changing, or bothersome hair on your face, jaw, chin, or chest, make sure to touch base with your dermatologist to understand if there is any underlying medical issue," Dr. Zeichner says. Getting checked out can rule out potential problems and help get you started on any necessary treatments.

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