Armpit hair, medically known as axillary hair, is a secondary sexual characteristic that typically begins during puberty. These hairs are sensitive to circulating sex hormones and are associated with apocrine sweat glands. While axillary hair serves functions like friction reduction and scent dispersal, its sudden or gradual loss can be concerning. Losing this hair is sometimes a normal part of aging, but it can also signal an underlying medical condition.
Systemic Hormonal Changes
The most common systemic causes of axillary hair loss involve fluctuations or deficiencies in hormones produced by the endocrine system. Hormones directly influence the hair follicle cycle (growth, regression, and rest). When the balance of these chemical messengers is disrupted, it can lead to a diffuse thinning or loss of hair across the body, including the armpits.
Thyroid hormones, specifically thyroxine (T4), regulate the hair growth cycle. In hypothyroidism, the thyroid gland produces insufficient hormones, slowing the hair cycle and prolonging the resting phase. This often causes diffuse hair loss on the scalp and noticeable thinning in the armpit area. Successful treatment of the underlying thyroid disorder typically reverses the hair loss, though regrowth takes several months.
The natural decline of sex hormones, particularly androgens, is another major factor driving axillary hair loss. Dehydroepiandrosterone (DHEA) and its sulfate form (DHEAS) are weak adrenal androgens responsible for maintaining this secondary sexual hair. As men and women age, hormonal shifts related to andropause or menopause lead to a gradual reduction in DHEA and DHEAS production. This age-related androgen decline is a frequent reason for the thinning or complete loss of armpit hair in later life.
Adrenal gland dysfunction can also cause abrupt hormonal deficiency leading to axillary hair loss. Addison’s disease, an autoimmune condition damaging the adrenal glands, results in a deficiency of several adrenal hormones, including DHEA. Low DHEA levels directly correlate with the loss of armpit and pubic hair, alongside other symptoms like fatigue and skin hyperpigmentation. The loss of this hair serves as a specific indicator of adrenal androgen insufficiency in female patients.
Autoimmune and Localized Skin Conditions
Not all hair loss is caused by systemic hormonal shifts; some conditions directly target the hair follicle, leading to localized or patchy loss. The most prominent is Alopecia Areata (AA), an autoimmune disorder where the immune system mistakenly attacks hair follicles. While AA most commonly affects the scalp, it can occur anywhere on the body, resulting in distinct patches of hair loss in the armpit.
In its most severe form, Alopecia Universalis, the condition leads to the complete loss of all body hair, including axillary hair. Unlike the gradual thinning seen in hormonal issues, AA-related hair loss is typically non-scarring and presents as smooth, hairless patches. Patients with autoimmune thyroid diseases are statistically more likely to develop AA.
Localized inflammatory reactions and infections can also temporarily or permanently destroy hair follicles. Severe contact dermatitis, triggered by ingredients in deodorants or soaps, creates inflammation that can damage the follicle structure. This localized trauma can lead to temporary hair shedding once the inflammation resolves.
Folliculitis, an infection or inflammation of the hair follicles, can also be a cause, especially if recurrent or severe. If the inflammation is deep, it can cause permanent damage and scarring of the follicle, resulting in localized, irreversible hair loss. This type of loss is distinct because it is usually confined to the area of the skin disease, unlike systemic hormonal imbalances.
External Factors and Temporary Causes
In many instances, armpit hair loss stems from external, behavioral, or temporary physiological stresses rather than chronic disease. This category of hair loss is generally non-progressive and often reversible once the underlying cause is resolved.
Chronic physical trauma or friction can cause traction alopecia, where repeated pulling or rubbing leads to hair breakage or follicle damage. This results from wearing excessively tight clothing or aggressive scrubbing during hygiene routines. Such mechanical stress weakens the hair shaft and can prematurely pull the hair out.
Significant physical or emotional stress, acute illness, or rapid weight loss can trigger Telogen Effluvium (TE). TE causes a large number of hairs to prematurely enter the resting and shedding phases simultaneously. While often noticed on the scalp, this synchronized shedding can also affect body hair, typically manifesting two to four months after the stressful event.
Severe nutritional deficiencies can also induce TE, as the body redirects resources away from non-essential functions like hair growth. Deficiencies in key micronutrients such as iron, zinc, and certain B vitamins impair the rapid cell division necessary for healthy hair production. A lack of adequate protein intake can similarly disrupt the structural integrity and growth of hair.
Certain medications are known to disrupt the hair cycle as a side effect. Drugs used in chemotherapy, which target rapidly dividing cells, are a common cause of complete body hair loss. Other medications, including blood thinners, retinoids, and high doses of certain hormone treatments, can induce a TE-like response. Additionally, aggressive hair removal methods, such as repeated waxing or improper laser hair removal, can damage the follicle enough to cause permanent hair loss.
When to Seek Professional Diagnosis
While some axillary hair loss is a normal, age-related occurrence, a sudden or asymmetrical change warrants medical evaluation. It is advisable to consult a healthcare provider if the hair loss is accompanied by systemic symptoms suggesting a broader medical issue. These red flags include unexplained weight fluctuation, persistent fatigue, unusual skin changes, or irregular menstrual cycles.
A professional diagnosis is also necessary if the hair loss is rapid, extensive, or noticeably asymmetrical (affecting only one armpit). The diagnostic process often involves initial blood tests to check for underlying systemic issues, such as a full thyroid panel or analysis of adrenal and sex hormone levels. In localized cases, a dermatologist may perform a detailed skin examination or a small skin biopsy to determine if an autoimmune or scarring condition is present.