Anorexia nervosa (AN) is a severe eating disorder defined by self-starvation and an intense fear of gaining weight, leading to dangerously low body weight and malnutrition. When deprived of energy and nutrients, the body enters a survival state, prioritizing essential functions like heart and brain activity over non-essential processes, including hair growth. Hair changes are a common physical manifestation of AN, often resulting in noticeable thinning and shedding. This response is driven by the lack of nutritional building blocks combined with systemic hormonal shifts that signal the body to conserve energy.
Hair Loss Mechanisms: Telogen Effluvium and Lanugo
Starvation causes two distinct hair changes: Telogen Effluvium and Lanugo growth. Telogen effluvium is the primary cause of scalp hair thinning and shedding, resulting from a premature shift in the hair growth cycle. Hair follicles normally cycle through a growing phase (anagen), a transitional phase (catagen), and a resting phase (telogen) before shedding. Starvation acts as a physical stressor, shocking a large number of growing hairs into the resting, or telogen, phase. This premature entry into the resting phase leads to excessive shedding, typically noticeable two to four months after the onset of severe malnutrition.
Lanugo involves the growth of soft, fine, unpigmented hair on the body, commonly appearing on the face, back, and arms. Lanugo hair is a physiological adaptation, attempting to conserve heat due to the loss of insulating body fat. As the body attempts to regulate its core temperature, this downy hair grows as a protective mechanism. While scalp hair thins and sheds, the body produces this new hair as a sign of extreme nutritional deficit.
Nutritional Deficiencies That Disrupt Hair Growth
Hair follicles are highly metabolically active and require a constant supply of specific raw materials to produce keratin, the main protein component of hair. Severe calorie and nutrient restriction starves the hair follicle of these necessary components, directly impairing its ability to grow healthy strands. Insufficient protein intake means the body lacks the amino acids needed to construct keratin, leading to weakened hair structure prone to breakage and shedding.
Key Micronutrient Deficiencies
Iron deficiency, often measured by low ferritin levels, is a frequent complication of AN and a common cause of hair loss. Iron is necessary for proper cellular function, including the production of hair matrix cells. Low iron levels reduce the oxygen supply to the hair follicles, inhibiting the growth phase and contributing to excessive shedding. Micronutrients such as zinc and B vitamins, including biotin, act as cofactors in the metabolic processes of the hair follicle. A lack of these vitamins and minerals impedes the normal function of the follicle, slowing the growth rate and producing dry, brittle hair.
Hormonal Changes Driving Hair Loss
The hormonal response to starvation overrides normal bodily functions, contributing significantly to hair loss beyond nutrient scarcity. The body attempts to lower its overall metabolic rate to conserve energy, often resulting in non-thyroidal illness syndrome. This state is characterized by suppressed levels of active thyroid hormones, specifically triiodothyronine (T3), which slows metabolism and can trigger hair thinning.
Stress and Sex Hormones
Chronic stress from malnutrition elevates cortisol, released by the adrenal glands. Elevated cortisol levels can directly signal hair follicles to prematurely enter the resting phase, initiating Telogen Effluvium. Furthermore, the lack of body fat and energy disrupts the production of sex hormones, leading to hypogonadotrophic hypogonadism. This metabolic state results in low levels of estrogen and testosterone, hormones that support the growth and maintenance of healthy hair.
Timeline for Hair Recovery
The hair loss caused by AN is generally temporary and reversible, but recovery requires sustained nutritional rehabilitation and weight stabilization. Hair regrowth is a slow process dictated by the natural cycle of the hair follicle. Once the body begins receiving consistent, adequate nourishment, it can take several weeks for the excessive shedding to cease.
Noticeable regrowth, often appearing as “recovery bangs” around the hairline, typically begins three to six months after consistent nutritional recovery is established. The hair follicle must complete its cycle reset before the new, healthy anagen phase can take hold. Lanugo hair often resolves more quickly than scalp hair loss, falling out once the body restores enough insulating fat to regulate its temperature. Patience is necessary, as it may take up to a year or more for the hair to regain its pre-illness thickness and length.