Hair loss on the arms and legs, sometimes termed peripheral alopecia, is distinct from the more common forms affecting the scalp. Hair follicles on the limbs require a precise biological environment to successfully cycle through growth phases. When this environment is disrupted by systemic illness or local factors, hair production slows down or stops entirely. Understanding these underlying issues is necessary to determine why hair on the extremities begins to thin or disappear.
Circulatory and Vascular Impairment
One significant cause of hair loss on the lower extremities involves compromised blood flow. Hair follicles are metabolically active and rely on a continuous supply of oxygen and nutrients delivered via the bloodstream. If this supply is insufficient, the follicles cannot sustain the rapid growth phase required for healthy hair production.
This inadequate circulation is frequently a manifestation of Peripheral Artery Disease (PAD). PAD occurs when arteries, most commonly in the legs, narrow due to plaque buildup. This narrowing restricts blood flow, leading to ischemia, or lack of oxygen, in the affected tissues. The resulting chronic lack of perfusion starves the hair follicles, causing them to shrink and enter an early resting state, which manifests as thinning and shedding of leg hair.
Hair loss due to PAD typically affects the lower legs and feet, often presenting symmetrically. This symptom is frequently accompanied by other indicators of poor circulation, such as a shiny or pale appearance, coldness in the extremities, or wounds that heal slowly. The loss of hair in this distribution is a physical sign that an underlying vascular problem may be present, requiring medical evaluation.
Hormonal Imbalances and Systemic Conditions
Internal, body-wide factors that disrupt the hair growth cycle also contribute to peripheral hair loss. The endocrine system regulates hormones and plays a direct role in maintaining hair follicle function. Disruptions can cause follicles to prematurely exit the active growth phase (anagen) and enter the resting phase (telogen), leading to increased shedding.
The thyroid gland, for example, produces hormones that regulate metabolism. An underactive thyroid (hypothyroidism) can slow metabolic processes, including the hair growth cycle, resulting in diffuse thinning across the body, including the arms and legs. Correcting the underlying thyroid dysfunction often helps restore normal hair growth.
Chronic diabetes is another systemic condition impacting peripheral hair. Long-term high blood sugar levels can damage small blood vessels (microangiopathy) and nerves (neuropathy) in the extremities. This damage impairs the follicle’s ability to receive necessary signals and nourishment, contributing to sparse limb hair. Hormonal fluctuations, such as those occurring during menopause or related to Polycystic Ovary Syndrome (PCOS), can also affect body hair density on the limbs, depending on sensitivity to androgens.
Localized Dermatological and Mechanical Causes
Hair loss on the arms and legs can also stem from conditions restricted to the skin and follicles, or from external physical forces. One cause is the autoimmune condition Alopecia Areata, where the immune system attacks the hair follicles. Though commonly associated with the scalp, it can cause distinct, smooth, non-scarring patches of hair loss on the limbs. More extensive forms, such as alopecia universalis, lead to hair loss across the entire body.
Chronic inflammatory skin conditions, such as eczema or psoriasis, can also lead to localized hair thinning. Persistent inflammation or repetitive trauma from scratching can physically damage the hair follicle, interrupting its growth cycle. Treating the underlying skin condition is necessary to allow hair to regrow.
Mechanical friction, often called frictional alopecia, is a common localized cause. Constant rubbing against the skin, such as from tight clothing, restrictive socks, or occupational trauma, can gradually wear down the hair shaft and damage the follicle. Hair loss is typically seen in the direct area of friction, such as the lower legs from trouser rubbing or around tight ankles.
Finally, senescent alopecia, or age-related hair loss, is a non-pathological cause. As the body ages, hair follicles naturally shrink (miniaturization), producing hair that is shorter, finer, and less pigmented. This thinning is often more noticeable on the arms and legs, reflecting a slowing down of the hair production process.