Body hair loss usually signals a shift in hormones, nutrition, or immune function rather than a standalone condition. Unlike scalp hair loss, which gets most of the attention, thinning or disappearing hair on your legs, arms, underarms, or eyebrows often points to something systemic happening inside your body. The cause ranges from easily correctable deficiencies to conditions that need ongoing management.
Thyroid Problems Are a Leading Cause
Your thyroid gland controls the metabolic activity that keeps hair follicles cycling through growth, rest, and shedding phases. When thyroid hormones drop too low (hypothyroidism) or spike too high (hyperthyroidism), that cycle breaks down. About 33% of people with hypothyroidism and 50% of those with hyperthyroidism experience noticeable hair loss.
The patterns differ depending on which direction your thyroid is off. An underactive thyroid slows cell division in hair follicles, pushing them into a prolonged resting phase and delaying regrowth. The hair you do have tends to become coarse, dry, and brittle. A classic sign is losing the outer third of your eyebrows. An overactive thyroid, on the other hand, triggers oxidative damage to follicles, making hair fine and silky but weaker. Both can cause diffuse thinning across the scalp and body.
Your Immune System May Be Attacking Hair Follicles
Alopecia areata is an autoimmune condition where your immune system mistakes hair follicles for a threat and attacks them. It typically starts as round, smooth patches of hair loss on the scalp, but it can progress. In its most advanced form, called alopecia universalis, you lose all hair on both your scalp and body, including eyebrows, eyelashes, and body hair everywhere.
The progression isn’t inevitable. Many people with alopecia areata stay in the patchy stage. But if you’re noticing smooth, well-defined bald spots spreading beyond your head, this is worth investigating. Other autoimmune conditions, like lupus, can also cause widespread hair thinning.
Nutritional Gaps That Thin Body Hair
Hair follicles are metabolically demanding. They need a steady supply of iron, zinc, protein, and vitamin D to maintain normal growth cycles. When any of these run low, your body diverts resources to more critical functions, and hair production is one of the first things to slow down.
Iron deficiency is one of the most common nutritional triggers. It doesn’t always show up as full-blown anemia. Even subclinical low iron, where your levels are technically in range but on the low end, can push more follicles into the resting phase. Zinc deficiency has also been linked to hair loss, though the relationship is subtler than often claimed. In a large cross-sectional study, people with hair loss had slightly lower median zinc levels (96 vs. 99 µg/dL), but both groups fell within the normal range, suggesting that zinc alone is rarely the whole explanation.
Crash dieting and severe calorie restriction are particularly effective at triggering hair shedding. When your body senses nutritional scarcity, it deprioritizes hair growth quickly. Protein deficiency does the same thing, since hair is made almost entirely of a protein called keratin.
Hormonal Shifts Beyond the Thyroid
Body hair depends heavily on androgens, the hormones (including testosterone and its precursors) that drive hair growth in the underarms, pubic area, chest, and limbs. Any condition that lowers androgen levels can thin body hair noticeably.
Adrenal insufficiency is a clear example. Your adrenal glands produce a hormone called DHEA-S, which is a key building block for androgens. When adrenal function drops, DHEA-S falls with it. In women especially, this causes loss of underarm and pubic hair, reduced libido, and dry skin. Men may notice body hair thinning during periods of low testosterone from any cause.
Menopause and the hormonal shifts of perimenopause commonly thin body hair in women. Pregnancy can trigger a burst of shedding afterward (telogen effluvium), though this is usually temporary. Pituitary insufficiency, which disrupts the hormonal signals that control multiple glands at once, can also lead to widespread hair thinning.
Medications That Cause Hair Shedding
A surprisingly long list of common medications can trigger body hair loss as a side effect. The mechanism varies, but most either disrupt the hair growth cycle or damage follicles directly. Drug classes known to cause hair shedding include:
- Blood thinners (anticoagulants)
- Blood pressure medications, including beta-blockers, ACE inhibitors, and diuretics
- Cholesterol-lowering drugs
- Antidepressants and mood stabilizers
- Acne treatments containing vitamin A (retinoids)
- Hormonal birth control
- Hormone replacement therapy
- Anti-seizure medications
- NSAIDs (common over-the-counter pain relievers like ibuprofen)
- Immunosuppressants
- Thyroid medications
- Weight loss drugs
If your body hair loss started within a few weeks to months of beginning a new medication, the timing is worth noting. Hair shedding from drugs typically follows a telogen effluvium pattern, meaning it shows up two to three months after the triggering event because that’s how long it takes for follicles pushed into the resting phase to actually release the hair.
Aging Naturally Thins Body Hair
Not all body hair loss is pathological. Hair follicles shrink with age, producing thinner, shorter, and less pigmented hair over time. This process, sometimes called senescent alopecia, typically begins after age 50 and progresses gradually. It’s characterized by a permanent decrease in hair diameter and length across the body.
Several things drive this. Sebum production declines, leaving hair drier and more brittle. Hair fiber diameter peaks around age 40 in women and as early as 18 in men, then gradually decreases. Hormonal responsiveness changes, nutritional absorption becomes less efficient, and the follicles themselves sustain cumulative damage from both intrinsic aging and environmental exposure. After age 65, an estimated 53% of men and 37% of women show significant hair thinning. If you’re over 50 with no family history of pattern baldness and your body hair is gradually becoming finer, aging itself is the most likely explanation.
Scarring Conditions That Destroy Follicles
Most causes of body hair loss are nonscarring, meaning the follicle openings remain intact and regrowth is possible once the underlying issue is addressed. Scarring alopecia is different. In these conditions, inflammation permanently destroys the follicle, replacing it with scar tissue. Once that happens, hair cannot regrow in that spot.
Frontal fibrosing alopecia is one example that affects body hair. While it primarily causes a receding hairline, about 38.5% of patients also lose eyebrow hair. Limb and body hair loss can occur as well. The key distinction is whether the tiny openings where hair exits the skin are still visible. If they’ve disappeared, the loss may be permanent, which makes early evaluation important.
What Testing Looks Like
A standard workup for unexplained body hair loss typically includes blood tests for thyroid function, iron and ferritin levels, total iron-binding capacity, vitamin D, a complete blood count, and hormone levels including testosterone and DHEA-S. In premenopausal women, this panel catches the majority of systemic causes.
Your doctor will also examine the areas of hair loss to check whether follicle openings are still present. That single observation separates reversible from potentially permanent causes and determines whether further investigation like a skin biopsy is needed.
How Long Regrowth Takes
Once the underlying cause is identified and treated, body hair generally takes longer to recover than scalp hair. Scalp hair grows faster and enters the growth phase more readily. You can expect soft, fine regrowth to appear within a few weeks of correcting the problem, but it takes a month or more for hair with normal texture and thickness to come in. Eyebrows and eyelashes tend to be the slowest to return.
For nutritional and hormonal causes, the timeline depends on how quickly your levels normalize. Thyroid-related hair loss often improves within several months of stable thyroid treatment. Telogen effluvium from stress, illness, or medication usually resolves on its own within six to nine months once the trigger is removed. Autoimmune hair loss is less predictable and may require ongoing treatment to maintain regrowth.