Does Keytruda cause hair loss? It is a question many patients ask when starting pembrolizumab, one of the most widely used cancer immunotherapies in the UK. Keytruda works differently from traditional chemotherapy, and its effects on hair reflect that distinction. Whilst hair loss is a recognised side effect listed in the MHRA-approved Summary of Product Characteristics, it is generally less common and less severe than chemotherapy-induced alopecia. In some cases, pembrolizumab can trigger an immune-related form of hair loss called alopecia areata. This article explains what to expect, how to manage hair changes, and when to contact your oncology team.

Does Keytruda Cause Hair Loss?

Yes, hair loss is a recognised side effect of Keytruda listed in the MHRA-approved SmPC, though it is generally less common and less severe than chemotherapy-induced alopecia; pembrolizumab can also trigger immune-mediated alopecia areata.

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Keytruda (pembrolizumab) is a type of cancer immunotherapy known as a PD-1 inhibitor. It works by blocking the programmed death-1 (PD-1) receptor on T-cells, releasing the immune system's natural brakes and allowing it to recognise and attack cancer cells more effectively. It is approved by the Medicines and Healthcare products Regulatory Agency (MHRA) and the European Medicines Agency (EMA) for a wide range of cancers, including melanoma, non-small cell lung cancer, and certain head and neck cancers.

Hair loss (alopecia) is listed in the Keytruda Summary of Product Characteristics (SmPC), as approved by the MHRA and EMA, as a recognised side effect. However, it is generally less common and less severe than the hair loss associated with traditional chemotherapy. Individual responses to immunotherapy vary considerably, and some patients report noticeable hair thinning or shedding during treatment.

In addition to general hair thinning, pembrolizumab can occasionally trigger an immune-related adverse event (irAE) called alopecia areata — an autoimmune condition in which the immune system mistakenly attacks hair follicles. This has been reported with immune checkpoint inhibitors as a class; the precise frequency is not well established in the SmPC and is based largely on post-marketing reports and published case series. Alopecia areata is distinct from the diffuse hair thinning sometimes seen with chemotherapy and may present as patchy hair loss. If you notice any sudden or patchy hair loss during treatment, report this to your oncology team promptly, as it may indicate an immune-related reaction requiring assessment.

If you experience a side effect you believe may be related to Keytruda, you can also report it directly to the MHRA via the Yellow Card Scheme at yellowcard.mhra.gov.uk.

How Common Is Hair Loss With Pembrolizumab?

Alopecia is classified as a common adverse reaction in the Keytruda SmPC, occurring in fewer than 1 in 10 patients, with complete hair loss being uncommon when pembrolizumab is used alone.

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According to the MHRA/EMC-approved Keytruda SmPC, alopecia is classified as a common adverse reaction, defined as occurring in ≥1/100 to <1/10 patients (i.e., in fewer than 1 in 10 people). The severity is typically mild to moderate; complete hair loss, as is frequently seen with cytotoxic chemotherapy, is uncommon with pembrolizumab alone.

The frequency of alopecia areata — the immune-mediated form of hair loss — is not precisely quantified in the SmPC. It has been documented in post-marketing surveillance and published case series of patients receiving immune checkpoint inhibitors. Some pharmacovigilance data suggest that checkpoint inhibitors as a class carry a small but recognised risk of triggering autoimmune skin and hair conditions, including alopecia areata and, in rarer cases, alopecia universalis (total body hair loss). Patients and clinicians should be aware of this possibility, even if it is uncommon.

It is also important to consider that many patients receiving Keytruda are on combination regimens that include chemotherapy agents, which are well-established causes of hair loss. In these cases, it can be difficult to attribute hair loss solely to pembrolizumab. The frequency of alopecia may also vary depending on the specific cancer type and treatment regimen. Your oncology team will be best placed to help identify the likely cause based on your individual treatment plan.

Overall, whilst hair loss is a recognised possibility with Keytruda, it affects a minority of patients and is rarely as pronounced as that associated with conventional chemotherapy.

Why Immunotherapy Affects Hair Differently to Chemotherapy

Unlike chemotherapy, pembrolizumab does not directly target dividing cells such as hair follicles; instead, it modulates the immune system, which can occasionally cause immune-mediated alopecia areata as an irAE.

To understand why Keytruda affects hair differently, it helps to consider how each treatment works at a cellular level. Chemotherapy drugs target rapidly dividing cells throughout the body — including cancer cells, but also healthy cells such as those in hair follicles. This non-selective mechanism is why chemotherapy so frequently causes widespread, often complete, hair loss that typically begins within two to four weeks of starting treatment.

Immunotherapy, by contrast, does not directly attack dividing cells. Instead, pembrolizumab modulates the immune system by blocking the PD-1 checkpoint pathway, allowing T-cells to become more active against tumour cells. Hair follicles are not directly targeted by this mechanism, which is why significant hair loss is far less common with immunotherapy than with chemotherapy.

However, because pembrolizumab enhances immune activity broadly, it can occasionally trigger immune-related adverse events (irAEs) — conditions where the activated immune system mistakenly attacks healthy tissues. The skin and its appendages, including hair follicles, can be affected in this way. Immune-mediated alopecia areata is one such irAE and is thought to result from T-cell infiltration of the hair follicle bulb, as described in dermatology and oncology literature on checkpoint inhibitor toxicity. This type of hair loss:

• May appear as round, patchy bald areas rather than diffuse thinning

• Can affect the scalp, eyebrows, eyelashes, or body hair

• May develop weeks to months into treatment

• Is potentially reversible, though this varies between individuals and is not guaranteed

• Is graded in severity using the Common Terminology Criteria for Adverse Events (CTCAE), which guides clinical management

Understanding this distinction is clinically important, as the management approach differs significantly from chemotherapy-induced alopecia.

Managing Hair Changes During Keytruda Treatment

Report any new or worsening hair loss to your oncology team; management ranges from gentle hair care for mild thinning to dermatology-guided corticosteroids for immune-mediated alopecia areata.

If you experience hair thinning or loss during Keytruda treatment, there are several practical steps and clinical considerations that may help. First and foremost, any new or worsening hair loss should be reported to your oncology team so that the cause can be properly assessed and documented. This is particularly important if the hair loss is patchy, rapid, or accompanied by other skin changes.

For mild, diffuse hair thinning, general hair care advice includes:

• Using gentle, sulphate-free shampoos and avoiding excessive heat styling

• Avoiding tight hairstyles that place tension on the hair shaft

• Eating a balanced diet to support overall nutritional status

• Discussing any nutritional supplements with your oncology team before taking them — in particular, high-dose biotin (vitamin B7) supplements should be avoided unless specifically advised by your clinician, as biotin can interfere with certain laboratory tests, including thyroid function tests, which are relevant during immunotherapy monitoring

• Requesting a referral to a dermatologist if hair loss is significant, distressing, or suspected to be immune-mediated

Scalp cooling (cold cap therapy) is a technique used to reduce chemotherapy-induced hair loss by restricting blood flow to the scalp during infusion. It is not indicated for immune-mediated alopecia areata associated with immunotherapy, and is therefore unlikely to be appropriate for pembrolizumab-related hair changes. Your oncology team can advise whether scalp cooling is relevant to your specific treatment regimen.

For immune-mediated alopecia areata specifically, management may involve topical or intralesional corticosteroids, guided by dermatology, depending on the extent and severity. In some cases, the oncology team may need to weigh the benefits of continuing pembrolizumab against the severity of the immune-related reaction. Dose interruption or discontinuation is rarely required for hair-related irAEs alone, but this decision is always made on an individual basis in line with recognised immunotherapy toxicity management frameworks, such as those published by the UK Oncology Nursing Society (UKONS).

Emotional and psychological support is equally important. Hair loss, even when partial, can significantly affect body image and quality of life. Many cancer centres offer access to wig fitting services and psychological support. Wig provision on the NHS varies across the four UK nations and between NHS Trusts — in some areas wigs are available free of charge or at a reduced cost to patients undergoing cancer treatment, whilst in others a charge may apply. Ask your clinical nurse specialist (CNS) or GP about what is available locally, or visit the NHS 'Wigs and fabric supports' page (nhs.uk) for further information.

When to Speak to Your Oncology Team

Contact your oncology team promptly if you notice sudden, patchy, or rapidly progressing hair loss, especially if accompanied by skin changes or other new symptoms suggesting a broader immune-related reaction.

Whilst mild hair thinning during Keytruda treatment may not require urgent intervention, there are specific circumstances in which you should contact your oncology team promptly. Early reporting of potential immune-related adverse events is a cornerstone of safe immunotherapy management, as timely intervention can prevent complications from escalating.

You should contact your oncology team or seek medical advice if you notice:

• Sudden or rapidly progressing hair loss, particularly if it is patchy or affecting eyebrows and eyelashes

• Skin changes accompanying hair loss, such as redness, scaling, or rash on the scalp

• Hair loss alongside other new symptoms, such as fatigue, joint pain, or changes in bowel habits, which could indicate a broader immune-related reaction

• Significant psychological distress related to changes in your appearance

• Any new symptom that concerns you, even if you are unsure whether it is related to your treatment

Your oncology team may refer you to a dermatologist for specialist assessment of scalp and hair changes. In the UK, the recognition and management of immune-related adverse events from checkpoint inhibitors is guided by frameworks including the UKONS Immunotherapy Toxicity Management Guidelines and NHS Acute Oncology Service pathways. Most cancer centres have established multidisciplinary pathways for managing irAEs, and specialist dermatology input is typically sought for suspected immune-mediated alopecia areata.

Do not wait until your next scheduled appointment if you are concerned — most oncology units have a dedicated 24-hour helpline or acute oncology service that can provide advice between appointments. Prompt communication with your clinical team is always the safest course of action.

You can also report any suspected side effects from Keytruda to the MHRA via the Yellow Card Scheme at yellowcard.mhra.gov.uk.

NHS Support and Resources for Cancer Treatment Side Effects

NHS support includes oncology nurse specialists, dermatology referrals, and wig provision (eligibility varies by UK nation and Trust); Macmillan Cancer Support and Alopecia UK also offer practical and emotional resources.

The NHS offers a range of support services for patients experiencing side effects from cancer treatments, including immunotherapy. Your first point of contact should always be your oncology nurse specialist or consultant, who can provide personalised guidance based on your treatment plan and medical history. Most NHS cancer centres also have access to allied health professionals, including dermatologists, dietitians, and clinical psychologists, who can support patients through treatment-related side effects.

For hair loss specifically, NHS wig provision varies across England, Scotland, Wales, and Northern Ireland, and between individual NHS Trusts. In some areas, wigs are available free of charge or at a subsidised cost to patients undergoing cancer treatment; in others, a standard charge applies. It is worth asking your CNS or GP about what is available in your area. Further information on eligibility and charges can be found on the NHS 'Wigs and fabric supports' page at nhs.uk.

If immune-mediated alopecia areata is suspected, your oncology team should refer you to a dermatologist, who is the appropriate NHS specialist for assessment and management of this condition. Trichologists (non-medical hair and scalp specialists) are not part of the standard NHS pathway for immune-mediated alopecia, though some patients choose to access trichology services privately as a complementary option.

Beyond clinical services, several charities and organisations offer practical and emotional support:

• Macmillan Cancer Support (macmillan.org.uk) provides information on managing side effects and financial support for people affected by cancer

• Cancer Research UK (cancerresearchuk.org) offers detailed, evidence-based information on pembrolizumab (Keytruda) and immunotherapy side effects

• Alopecia UK (alopecia.org.uk) provides peer support and resources specifically for those experiencing hair loss, including alopecia areata

• The NHS website (nhs.uk) contains patient-friendly information on pembrolizumab and immunotherapy side effects, including the NHS Medicines A–Z entry for pembrolizumab

Remember that experiencing side effects does not necessarily mean your treatment is not working. Many patients on Keytruda tolerate it well and continue to benefit from treatment. Open communication with your healthcare team remains the most effective way to manage any concerns that arise throughout your cancer journey.

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