Chemotherapy-induced hair loss (alopecia) is a recognized side effect of cancer treatment. While scalp hair loss receives the most attention, patients are often concerned about how treatment affects facial hair, including beards, mustaches, eyebrows, and eyelashes. Understanding the specific mechanisms and timelines helps set expectations.
How Chemotherapy Affects Hair Follicles
Chemotherapy drugs target and destroy rapidly dividing cells, a defining characteristic of cancer cells. Unfortunately, the matrix cells within hair follicles are among the fastest-dividing cells in the body, making the follicle an unintended target of systemic treatment.
The resulting hair loss is classified as anagen effluvium, a sudden, widespread shedding caused by toxic insult to the hair root during its active growth phase. The drugs impair cell division, causing the hair shaft to narrow and break off near the skin’s surface. The severity of hair loss depends heavily on the specific drug regimen, dosage, and treatment schedule. Certain drug classes, like taxanes and anthracyclines, are associated with higher rates of complete hair loss.
Hair Loss Specific to Facial Features
The susceptibility of facial hair follicles compared to scalp hair is largely determined by their respective growth cycles, particularly the anagen phase, where the matrix cells are most vulnerable. Scalp hair has a lengthy anagen phase that can last anywhere from two to seven years, meaning a high percentage of follicles are actively growing and susceptible to damage at any time.
Beard and mustache hair also have a relatively long anagen phase, often lasting several months to a couple of years, which is why they are frequently affected by chemotherapy drugs, sometimes almost as severely as scalp hair. However, the follicles for eyebrows and eyelashes operate on a much shorter cycle. The anagen phase for an eyelash lasts only about four to eight weeks, while eyebrows are in the growth phase for approximately two to seven months.
Because the growth phase is significantly shorter for eyelashes and eyebrows, a smaller percentage of these follicles are actively dividing and vulnerable when the chemotherapy agent is in the system. This difference explains why the loss of eyebrows and eyelashes is more variable and generally less complete than the loss of scalp or beard hair. While loss of eyebrows and eyelashes can happen, with some studies showing involvement in up to 33% of patients on certain regimens, the shorter cycle means that even if the active hairs are damaged, a new growth cycle can begin relatively quickly once the drug is cleared.
Timeline for Loss and Regrowth
Hair loss typically begins quickly, starting two to four weeks after the first chemotherapy session. Patients may notice hair shedding in large amounts, sometimes accompanied by tenderness or a tingling sensation in the scalp.
Facial hair, including eyebrows and eyelashes, may follow a slightly delayed timeline compared to the scalp. Shedding continues throughout the treatment period and for a few weeks after the last dose, as the cytotoxic agents clear from the body.
Regrowth typically begins within two to four weeks following the cessation of treatment. This initial regrowth often presents as fine, soft, colorless hair, sometimes referred to as “peach fuzz.” Over the next few months, the hair becomes thicker and more pigmented, with significant visible growth generally seen between three and six months. New hair may temporarily differ in texture or color, such as growing back curlier than before, a phenomenon sometimes called “chemo curls,” but it usually returns to its original characteristics within a year.