High levels of the hormone prolactin can contribute to hair loss, a condition known as hyperprolactinemia. Prolactin is primarily recognized for its role in milk production, but its imbalances affect various systems, including the hair growth cycle. This article explores the link between elevated prolactin and hair shedding, detailing the mechanisms of disruption, common causes, and medical approaches for diagnosis and treatment.
Prolactin: A Hormone Beyond Lactation
Prolactin (PRL) is a protein hormone secreted mainly by the pituitary gland. While its primary function is stimulating milk production after childbirth, prolactin influences over 300 physiological processes. These include reproductive health, where it regulates the menstrual cycle and fertility by inhibiting hormones like Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH).
The hormone also plays a role in metabolism, fluid balance, and immune system modulation. Normally, prolactin levels are kept low through the inhibitory action of the neurotransmitter dopamine. Abnormally high prolactin levels cause hyperprolactinemia, which leads to symptoms beyond reproductive dysfunction.
The Direct Link: How Hyperprolactinemia Disrupts the Hair Cycle
Elevated prolactin interferes with the normal life cycle of the hair follicle. Hair growth consists of three main phases: the growing phase (anagen), the transitional phase (catagen), and the resting/shedding phase (telogen). Prolactin receptors are present in human scalp hair follicles, making them a direct target for the hormone’s signaling.
High concentrations of prolactin prematurely push the hair follicle from the active anagen phase into the regressive catagen phase. This shortens the lifespan of growing hair, causing a greater proportion of hairs to enter the telogen phase simultaneously. The resulting excessive shedding is often recognized as telogen effluvium, a diffuse hair loss pattern across the scalp.
Hyperprolactinemia also indirectly affects hair health by suppressing the reproductive axis, leading to lower levels of hormones that support robust hair growth. Prolactin has also been implicated in modulating androgen metabolism, sometimes contributing to a hair loss pattern resembling androgenetic alopecia in women.
Identifying the Root Cause of Elevated Prolactin
Identifying the underlying cause of hyperprolactinemia is necessary for effective management.
Prolactinoma
One frequent pathological cause is a prolactinoma, a benign tumor of the pituitary gland that secretes excess prolactin. These tumors are responsible for a high percentage of consistently high prolactin levels and are the most common type of pituitary tumor.
Medication Side Effects
Medication-induced hyperprolactinemia is another prevalent cause, as numerous drugs interfere with dopamine’s ability to suppress prolactin release. Medications such as certain antipsychotics, antidepressants, high blood pressure medications, and high-dose estrogen therapy can elevate prolactin levels by disrupting the normal inhibitory feedback loop.
Systemic Conditions
Other systemic conditions also contribute to the elevation, including an underactive thyroid gland (hypothyroidism) and chronic kidney failure. Hypothyroidism increases the release of Thyrotropin-Releasing Hormone (TRH), which stimulates prolactin secretion. Physiological factors like intense physical stress or excessive exercise can also temporarily increase prolactin levels.
Diagnosis and Treatment Pathways
Diagnosis begins with a blood test to measure the serum prolactin level, typically considered elevated above 25 ng/mL in non-pregnant women. Because levels fluctuate due to stress, mild elevations may require a repeat measurement to confirm the diagnosis. If levels are significantly elevated or the cause is unclear, further imaging is recommended.
A Magnetic Resonance Imaging (MRI) scan of the pituitary gland is often performed to check for a prolactinoma or other lesions. Treatment focuses on normalizing prolactin levels once the underlying cause is determined.
For prolactinomas and idiopathic hyperprolactinemia, the first-line treatment is medication with dopamine agonists, such as cabergoline or bromocriptine. These medications mimic dopamine, binding to pituitary receptors to inhibit prolactin secretion and often shrink tumors. If medication is the cause, a doctor may adjust the dosage or switch to an alternative drug. Successful treatment usually leads to a reversal of the associated hair loss.