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Key considerations in the diagnosis and management of drug-induced alopecia include the timing of onset, biologic plausibility, underlying pathophysiologic mechanism, and, in some cases, scalp biopsy findings, according to Jorge Larrondo Gálvez, MD , surgeon and specialist in dermatology and trichology in the Department of Dermatology, Clínica Alemana-Universidad del Desarrollo, Santiago, Chile.

Gálvez holds a MSc in trichology and hair transplantation. He coordinates with the Hair and Nail Group of the Chilean Society of Dermatology and Venereology and serves the Scientific Program Committee of the American Hair Research Society.

He discussed the topic during a session at the 43rd Annual Meeting of Latin American Dermatologists (RADLA 2026) in Buenos Aires, Argentina.

Speaking with Medscape’s Spanish edition, Larrondo, said, “Sometimes there is a tendency to quickly blame the medication without actively investigating whether a causal relationship is plausible. At other times, traditional diagnoses are made without considering or reviewing the medications a patient has been taking, especially during the previous 3 months. We need to be very thorough in our evaluation.”

He noted that in the normal hair cycle, 85%-90% of hair follicles are in the anagen, or growth, phase; fewer than 1% are in the catagen, or transitional, phase; and 10%-15% are in the telogen, or resting, phase, which lasts for 2-4 months.

Hair responds to injury in a certain way: It stops growing, enters a resting phase, becomes inflamed, or changes in quality. Drug-induced follicular damage generally falls into four categories: anagen effluvium (abrupt hair shedding) or telogen effluvium (premature resting and shedding), which can result in hair miniaturization, texture changes, and altered cycling.

Anagen Effluvium

Anagen effluvium results from direct damage to the proliferative hair matrix. The most characteristic example is alopecia, which develops days to weeks after the initiation of cancer chemotherapy.

“It can be tremendously dramatic. Fourteen percent of patients even consider refusing chemotherapy because they know this is likely to happen,” Larrondo said.

The most effective preventive approach for anagen effluvium/chemotherapy-induced hair loss is scalp cooling, in which cooling caps are applied before, during, and for up to 2 hours after chemotherapy administration.

“It is painful, labor intensive, and not available in all centers. However, large studies, primarily in breast cancer, have shown effectiveness ranging from 50%-60%, although results vary considerably depending on the chemotherapy regimen and baseline patient characteristics,” he said.

The approach appears to be most effective with non-anthracycline taxane regimens, including docetaxel and paclitaxel. Reported adverse effects include headaches, nausea, and dizziness.

Hair generally regrows within 6 months after the completion of chemotherapy. However, persistent chemotherapy-induced alopecia can occur and may be treated with topical minoxidil 5%, oral minoxidil at doses ranging from mg/d 0.5 to 5 mg/d, or spironolactone at doses up to 200 mg/d.

Telogen Effluvium

Telogen effluvium is a common form of hair loss caused by the premature entry of hair follicles into the telogen phase. Although patients often blame the most recently initiated medication, the actual trigger may have occurred 2-4 months earlier.

“For example, it may be related to low iron levels, vitamin D deficiency, vitamin B12 deficiency, hypothyroidism, or weight loss. It can also be an early warning sign of systemic disorders such as lupus or other systemic diseases,” Larrondo said.

Numerous medications can trigger telogen effluvium, including retinoids, which may also alter hair texture and shaft fragility, anticoagulants, beta blockers, antithyroid agents, anticonvulsants, lithium, interferons, and GLP-1 receptor agonists.

“In the case of GLP-1 receptor agonists, it is well recognized that telogen effluvium may occur when substantial weight loss occurs rapidly,” he noted.

If alternative causes have been excluded and one of these medications was initiated within the previous 3 months, “it may well be the culprit.”

Larrondo also recommended oral minoxidil when the implicated medication cannot be discontinued or replaced.

“I would start with a low dose and gradually increase it until the shedding decreases,” he said.

Inflammatory Alopecia

Targeted therapies, including small-molecule agents and monoclonal antibodies, can cause diffuse nonscarring alopecia in approximately 15% of cases and primary scarring alopecia in about 5%, sometimes with rapid progression.

A classic example is vismodegib, a selective inhibitor of the sonic hedgehog signaling pathway, used to treat basal cell carcinoma.

“The sonic hedgehog pathway is also critical for initiating and maintaining the anagen phase. When hair cannot enter this phase, minoxidil, finasteride, and dutasteride are ineffective. What works is completing the treatment cycle, after which hair growth generally resumes,” Larrondo said.

Epidermal growth factor receptor inhibitors can cause severe inflammatory scalp reactions resembling erosive pustular dermatoses.

“In these situations, the recommendation is not to stop treatment but to manage the inflammatory response with tetracyclines or topical or intravenous corticosteroids,” he said.

Immune checkpoint inhibitors, including nivolumab, pembrolizumab, and durvalumab, as well as anti-CD20 therapies, such as rituximab, can also trigger inflammatory hair disorders. These reactions are characterized by increased numbers of follicles in the catagen or telogen phase and can resemble alopecia areata or scarring alopecia in 1%-2% of patients.

Julia Riganti, MD, dermatologist , specialist in adverse drug reactions from the Hospital Italiano de Buenos Aires in Buenos Aires, Argentina, who also participated in the session, noted that alopecia areata occurs more commonly with PD-1 inhibitors.

She emphasized that these cases can be managed with topical or intralesional corticosteroids and that discontinuation of immunotherapy is generally not indicated.

Paradoxical Effects

Drug-induced alopecia can sometimes be unexpected.

In a case report published in April in The American Journal of Dermatopathology, Larrondo and colleagues described a 50-year-old woman who developed severe diffuse hair loss 6 months after starting dupilumab for atopic dermatitis, despite achieving good disease control.

Trichoscopy revealed black dots, broken hair, and solitary circular hair. Biopsy demonstrated anisotrichosis, increased catagen and telogen follicles, and lymphocytic infiltration surrounding the follicular bulb.

The patient was diagnosed with alopecia areata incognita. After the dupilumab dose was reduced by half, hair regrew.

“This is another alternative for managing these patients,” Larrondo said.

He acknowledged the paradoxical nature of this finding because dupilumab has also been proposed as a treatment for alopecia areata.

Hair Changes

Hair color and texture changes may also occur in nearly one third of patients receiving targeted therapies.

“Some patients tell me their hair has become curlier, or that their eyelashes have become longer,” Larrondo said. “You may also see patients whose gray hair regains pigment, while others with pigmented hair develop completely gray hair.”

In many cases, hair returns to its original appearance after the medication is discontinued.

“It is very interesting, but there is still much more to investigate,” he added.

Retinoids have also been implicated in these changes.

Endocrine Therapy

Larrondo noted that 20%-30% of women receiving endocrine therapy for breast cancer, including tamoxifen, anastrozole, or leuprolide, develop alopecia resembling female- or male-pattern hair loss, characterized by follicular miniaturization and substantial effects on quality of life.

Minoxidil and spironolactone may be safe options for limiting and reversing this form of hair loss.

“It is important to bring together all available tools to achieve an accurate diagnosis and appropriate treatment. Biopsies obtained from representative sites are extremely useful, but the most important factors remain the clinical presentation, a thorough history, a detailed physical examination, the timing of medication exposure, when treatment began, and whether the drug has any reported adverse effects.”

“Often we feel frustrated because we do not know the connection between a drug and hair loss. However, we all make mistakes, and none of us can know every newly reported adverse effect. You can take notes, do some research, and if there is a plausible mechanism by which a drug could cause alopecia, contact the patient and proceed accordingly.”

Larrondo reported having no relevant conflicts of interest. Riganti disclosed receiving honoraria from Johnson & Johnson, Adium, and Unilever.

This story was translated from Medscape’s Spanish edition.