The idea that hair loss increases around menstruation is a common observation, often leading to questions about the body’s monthly cycle and hair health. Hair shedding is a natural and continuous process occurring across the scalp daily. This article explores the physiological reality behind this observation, examining how reproductive hormones influence the hair growth cycle.
Understanding the Hair Growth Cycle
Hair follicles operate on a continuous, independent cycle involving periods of growth and rest. The vast majority of hair is in the Anagen phase, the active growing period that can last for several years. This phase determines the maximum length a person’s hair can reach.
Following the growth stage is the Catagen phase, a short transitional period lasting only a few weeks, where the hair follicle shrinks and detaches from its blood supply. The hair then enters the Telogen phase, a resting period of approximately two to four months, where the club hair is fully formed but remains in the follicle.
The cycle concludes with the Exogen phase, during which the old, resting hair strand is naturally released from the scalp. For most people, this constant cycling results in a normal daily loss of about 50 to 100 hairs. This shedding is necessary for the cycle to renew itself with new growth.
Hormonal Changes Governing Hair Shedding
The hair cycle is highly sensitive to shifts in reproductive hormones across the month. Throughout the follicular phase, estrogen levels steadily rise, playing a protective role by prolonging the hair’s active Anagen growth phase. Higher estrogen exposure means fewer hairs transition into the resting and shedding phases prematurely.
The second half of the cycle, the luteal phase, sees a significant rise and then a sharp drop in both estrogen and progesterone before the start of menstruation. This decline in supportive hormones can act as a physiological shock to the hair follicles. When a large group of follicles experiences this sudden hormonal reduction, they may be prematurely signaled to switch from the Anagen phase into the Telogen resting phase.
The shedding event that a person notices during their period is typically not a direct response to the hormone levels that day. Shedding triggered by a hormonal shift, known as telogen effluvium, is a delayed process. The hair that enters the Telogen resting phase waits two to three months before it is finally shed during the Exogen phase.
Therefore, any noticeable increase in hair loss during menstruation is the physical manifestation of a hormonal trigger that occurred weeks or months earlier. This delayed shedding is usually temporary, as the underlying hormonal trigger resolves itself in the subsequent cycle, allowing hair follicles to resume their normal growth pattern.
When Cyclical Shedding Becomes a Concern
While temporary, hormonally-linked shedding is common, other systemic factors can mimic or exacerbate hair loss. An underlying iron deficiency, common in individuals with heavy menstrual bleeding, significantly contributes to hair shedding because iron is necessary for producing hair cell proteins.
Thyroid imbalances (hyperthyroidism or hypothyroidism) also disrupt the hair growth cycle and can cause noticeable hair thinning. Extreme physical or psychological stress can trigger a more severe, acute bout of telogen effluvium, resulting in a sudden increase in hair loss. Certain medications, including hormonal contraceptives or blood pressure drugs, may also be a contributing factor.
It is advisable to consult a healthcare provider if the hair loss is more than just a temporary increase in shedding. Signs that warrant medical attention include noticeable overall thinning of hair density or a widening part that lasts longer than three to six months. Patchy hair loss, accompanied by irritation, or the loss of hair from other areas like the eyebrows, suggests an issue beyond normal cyclical variation and should be professionally evaluated.