Hair loss is a visible and often distressing side effect of a cancer diagnosis. Many people assume cancer itself causes this hair loss. However, in most cases, hair loss results from treatments, rather than the disease’s direct impact on hair follicles.
Hair Loss Primarily Due to Cancer Treatments
Many cancer treatments target rapidly dividing cells. Hair follicle cells are among the fastest-growing, making them unintended targets. Damage to these rapidly dividing hair cells disrupts the normal hair growth cycle.
Hair growth occurs in three main phases: anagen (active growth), catagen (transition), and telogen (resting). Chemotherapy drugs often push many hair follicles prematurely into the resting phase, leading to shedding. This broad impact on hair follicles across the scalp, and sometimes the entire body, is the primary reason for treatment-related hair loss.
Specific Treatments That Cause Hair Loss
Chemotherapy is the most common cause of hair loss in cancer patients. Potent drugs like doxorubicin, cyclophosphamide, and paclitaxel attack fast-growing cancer cells and rapidly dividing hair root cells. Hair loss typically begins two to four weeks after treatment starts, affecting hair on the scalp, eyebrows, eyelashes, and other body hair.
Radiation therapy can also induce localized hair loss. Hair loss occurs only in the treated area, as high-energy beams directly damage hair follicles within the targeted field. For example, head radiation causes scalp hair loss, while arm radiation affects only hair on that limb. Severity and potential for regrowth depend on the radiation dose; higher doses increase the likelihood of permanent hair loss.
Newer cancer treatments, including targeted therapies and immunotherapy, generally have a lower likelihood of causing complete hair loss than chemotherapy, but can still lead to hair changes or thinning. Some targeted therapies, like epidermal growth factor receptor (EGFR) inhibitors, can cause hair to become thin, dry, brittle, or curly. Immunotherapy agents may cause mild thinning or patchy hair loss, though less frequent and severe than chemotherapy-induced hair loss. Hormonal therapies, often used for breast cancer (e.g., tamoxifen, aromatase inhibitors), are also associated with hair thinning, which can persist for years during treatment.
When Cancer Itself Causes Hair Loss
While less common, certain cancers or related conditions can directly lead to hair loss, independent of treatment. One instance is paraneoplastic syndromes, where the immune system, in response to a tumor, mistakenly attacks healthy cells, including hair follicles. For example, alopecia areata, an autoimmune condition causing patchy hair loss, has been reported as a paraneoplastic manifestation in rare Hodgkin’s lymphoma cases.
Cancers can also indirectly cause hair loss by causing nutritional deficiencies. Malignancies increase the body’s metabolic needs and can reduce nutrient intake, depleting vitamins and minerals. Deficiencies in elements like iron, zinc, biotin, and certain B vitamins, all important for hair follicle function, can cause hair thinning or loss.
Hormonal changes induced by specific tumor types may also contribute to hair loss. Cancers affecting endocrine glands (e.g., ovarian or adrenal tumors) can disrupt hormonal balance. These imbalances, including altered levels of thyroid or sex hormones (e.g., estrogen, testosterone), can lead to diffuse hair thinning or shedding.
Factors Influencing Treatment-Related Hair Loss
Hair loss during cancer treatment is influenced by several interconnected factors. The specific type of chemotherapy drug plays a role, as some agents are more likely to cause complete hair loss, while others cause thinning. For example, high-dose cyclophosphamide and doxorubicin are associated with substantial hair loss, whereas platinum-based chemotherapies have a lower risk.
Medication dosage, frequency, and duration of treatment cycles also impact hair loss severity. Higher doses and more frequent administrations result in more pronounced and rapid hair shedding. When combination therapies are used, the cumulative effect of multiple drugs increase the likelihood and extent of hair loss.
Individual patient factors contribute to varying responses. Genetic predispositions, age, and pre-existing hair conditions influence how a person’s hair reacts to treatment. Overall health and nutritional status before and during treatment affect the hair follicles’ resilience. The state of the hair follicles at the time of treatment, specifically their growth cycle phase, also impacts the immediate shedding response.