A few cancers cause hair loss directly, but the far more common reason cancer patients lose their hair is treatment: chemotherapy, radiation, and hormone therapy. Understanding which cancers and which treatments lead to hair loss, and what to expect, can help you make sense of what’s happening and what comes next.
Cancers That Directly Cause Hair Loss
Most cancers don’t cause hair loss on their own. The ones that do typically involve the skin or blood, and they damage hair follicles either by infiltrating the scalp or by triggering immune responses that disrupt hair growth.
The clearest examples are two forms of cutaneous T-cell lymphoma: mycosis fungoides and Sézary syndrome. These are cancers of white blood cells that settle in the skin. In mycosis fungoides, hair loss is detectable within skin lesions in about 66% of cases. The hair falls out in patches where the cancerous cells have invaded, and clinicians are advised to consider cutaneous lymphoma whenever someone presents with unexplained scalp hair loss.
Plasmacytoma, a tumor of plasma cells related to multiple myeloma, can also cause hair loss as part of a paraneoplastic syndrome, meaning the body’s reaction to the cancer triggers the shedding rather than the tumor itself physically destroying follicles.
Certain tumors that produce excess androgens (male hormones) can accelerate hair thinning in a pattern similar to male-pattern baldness. Some adrenal adenomas fall into this category, causing hair loss through hormonal disruption rather than direct damage.
When Cancer Spreads to the Scalp
A less common but important cause is alopecia neoplastica, where cancer cells metastasize to the scalp and destroy hair follicles from within. This typically appears as a slowly expanding patch or plaque of scarring hair loss. In women, the most common source of these scalp metastases is breast cancer. The patch often looks like other types of hair loss, which can lead to misdiagnosis. If a scarring bald patch doesn’t respond to standard treatments, a biopsy is warranted because undetected alopecia neoplastica carries significant risks if the underlying cancer goes untreated.
Paraneoplastic Hair Loss
Some cancers trigger hair loss indirectly through the immune system or metabolic changes, even though the tumor is located nowhere near the scalp. This is called paraneoplastic alopecia, and its defining feature is that the hair loss follows the course of the cancer itself: when the cancer responds to treatment, the hair grows back, and if the cancer returns, so does the hair loss.
Cancers linked to paraneoplastic hair loss include malignant lymphomas (where deranged immune activity is thought to be the cause), cholangiocarcinoma (bile duct cancer), pancreatic cancer, and gastrointestinal stromal tumors. These associations are rare, but they underscore why new, unexplained hair loss sometimes prompts doctors to look deeper.
Chemotherapy and Hair Loss
For most cancer patients, hair loss comes from treatment rather than the disease. Chemotherapy-induced hair loss affects roughly 65% of all patients receiving chemo, though the rate varies enormously depending on the drug class.
The highest-risk chemotherapy drugs are anthracyclines, used for leukemia, lymphoma, sarcoma, and breast cancer. Hair loss occurs in 60 to 100% of patients on these regimens. Shedding typically begins one to three weeks after starting treatment and can progress to near-complete loss of scalp and body hair with continued cycles.
Taxanes, used for breast, lung, bladder, and several other cancers, cause hair loss in 60 to 80% or more of patients. With cumulative treatment, loss often extends beyond the scalp to eyebrows, eyelashes, and body hair. Alkylating agents cause hair loss at rates of 60% or higher. Antimetabolites are gentler on hair, with rates between 10 and 50%.
Hair usually starts falling out two to four weeks after chemotherapy begins. The loss continues throughout treatment and for a few weeks afterward. Regrowth typically starts three to six months after treatment ends, though the texture and color of new hair sometimes differ from what you had before.
Radiation Therapy
Radiation only causes hair loss in the area being treated. If you’re receiving radiation to the brain, you’ll lose hair on your scalp. If the treatment targets your pelvis, the hair on your head stays put.
Whether the loss is temporary or permanent depends on the dose. Doses in the range of 16 to 20 Gy typically cause temporary hair loss that recovers within a few months. At higher doses, around 40 to 43 Gy, the risk of permanent hair loss rises sharply. Research on brain cancer patients found that a follicle dose of 43 Gy is associated with a 50% chance of permanent hair loss. When the maximum scalp dose exceeds 30 Gy, nearly half of patients experience noticeable thinning in the treated area.
Hormone Therapy for Breast Cancer
Hormone therapies used after breast cancer treatment, including aromatase inhibitors and tamoxifen, cause a subtler but still distressing form of hair loss. About 25% of breast cancer patients on these medications experience hair thinning. Aromatase inhibitors work by blocking estrogen production, which causes a relative increase in androgen levels. That hormonal shift slows hair follicle growth in a pattern resembling male-pattern baldness. Tamoxifen pushes hair follicles into a prolonged resting phase, causing gradual thinning rather than sudden shedding.
This type of hair loss is less dramatic than chemotherapy-induced shedding, but it can last for years since hormone therapy is often prescribed for five to ten years. No large clinical trials have tested treatments specifically for this problem, which remains a frustrating gap for patients and doctors alike.
Immunotherapy
Checkpoint inhibitors, the immunotherapy drugs now used widely for melanoma and other cancers, cause hair loss at much lower rates than chemotherapy. Pembrolizumab is associated with patchy hair loss (alopecia areata) in about 0.9% of patients, and nivolumab in about 2%. When it does occur, the mechanism is autoimmune: the revved-up immune system mistakenly attacks hair follicles along with cancer cells.
Scalp Cooling and Hair Regrowth
Scalp cooling (cold caps worn during chemotherapy infusions) is the most established method for preventing chemo-related hair loss. The cold narrows blood vessels in the scalp, reducing how much drug reaches the hair follicles. Overall, about 53% of patients using scalp cooling avoid visible hair loss, with success rates between 50 and 65% depending on the drug regimen and cooling technique. Patients on taxane-only regimens fare best, with one study showing 100% hair retention for those on paclitaxel alone and 88% for those on other taxane combinations without anthracyclines.
For patients who do lose their hair, topical minoxidil may help speed regrowth after chemotherapy ends. One small trial found that women using 2% minoxidil twice daily saw their first signs of regrowth at an average of 87 days after maximum hair loss, compared to 137 days in the control group. Results across studies have been mixed, though a more recent approach combining low-dose oral minoxidil with topical minoxidil showed significantly better hair density improvements than topical treatment alone in patients with persistent or prolonged post-chemo hair loss.