Persistent alopecia after chemotherapy (PACIA): understand, recognize, act.
Definition, frequency, mechanisms, risk factors and management of long-lasting incomplete regrowth after chemotherapy.
Persistent chemotherapy-induced alopecia (PACIA) is non-scarring alopecia that persists for more than 6 months after the end of chemotherapy. It is characterized by absent or incomplete regrowth. This definition is the subject of an international consensus of experts published in 2025.
PACIA is hair loss that does not recover — or only partially — more than six months after the end of chemotherapy. Long considered rare, it turns out to be more common than previously thought: according to a three-year cohort study, nearly 40% of patients present with incomplete regrowth at six months. Treatments based on taxanes are the most in question. The mechanism involves damage to the stem cells of the follicle. An expert consensus published in 2025 specifies the definition, diagnosis and management. This article provides a complete update on PACIA.
PACIA (persistent chemotherapy-induced alopecia) refers to absent or incomplete regrowth persisting more than 6 months after the end of treatment, according to the international expert consensus of 2025. It would concern nearly 40% of patients at 6 months according to a cohort study, especially after taxane-based treatments. The mechanism involves depletion or destruction of follicle stem cells. The period following the last session is decisive: restoring the capillary surface early - through an early reconstruction treatment like REDACTIV 1, the day after the last chemo - offers the follicle better conditions for regrowth. A PACIA installed requires medical advice.
Qu'est-ce que la PACIA ?
After chemotherapy, hair regrows in the vast majority of cases. But in some patients, regrowth does not return, or returns markedly insufficient, months after the end of treatment. This is called chemotherapy-induced persistent alopecia — PACIA, or pCIA.
An international consensus of experts, established by the Delphi method and published in 2025, set the definition: non-scarring alopecia which persists more than six months after the end of chemotherapy. “Non-scarred” means that the follicle is not destroyed by a scar — it exists, but does not produce satisfactory hair. This clarification is important because it distinguishes PACIA from other forms of permanent alopecia.
- PACIA is absent or incomplete regrowth more than 6 months after chemotherapy.
- It is a non-scarring alopecia: the follicle exists but does not produce satisfactory hair.
- Its definition is the subject of an international consensus of experts in 2025.
A frequency long underestimated
PACIA has long been considered rare. Recent data shows that it is significantly more common than previously thought, particularly after certain protocols.
Depending on the protocol, the figures vary greatly. A British study reported significant PACIA in 10.1% of patients treated with paclitaxel and 23.3% of those treated with docetaxel. At three years, the patients concerned mainly report thinning of the hair (75%) and a reduction in hair volume (54%).
- Kang D. et al., Permanent Chemotherapy-Induced Alopecia in Patients with Breast Cancer: A 3-Year Prospective Cohort Study, The Oncologist, 2019 (PACIA 39.5% at 6 months, 42.3% at 3 years; slimming 75%, reduced volume 54% at 3 years).
- Review of the literature on the regimen-specific incidence of persistent alopecia (paclitaxel 10.1%, docetaxel 23.3%; combinations up to 52%).
The mechanism: l'atteinte des cellules souches
Why doesn't the follicle start again normally? The mechanism currently accepted involves the stem cells of the hair follicle. Located in an area called the bulge, these cells are responsible for hair renewal each cycle.
According to consensus work, PACIA results from a depletion or destruction of these stem cells after chemotherapy. When the reservoir of stem cells is depleted, the follicle loses all or part of its capacity to produce new hair: regrowth becomes absent, slow or sparse. This is what distinguishes PACIA from simple delayed regrowth, where the stem cells are preserved.
- La PACIA implique une atteinte des cellules souches du follicule (zone du bulge).
- Their depletion or destruction reduces the ability of the follicle to produce hair.
- This is what distinguishes it from simply delayed regrowth.
Les facteurs de risque
Not all patients have the same risk of CAIP. Recent work identifies several factors that increase it.
| Facteur de risque | Precision |
|---|---|
| Type of chemotherapy | Protocols based on taxanes (docetaxel, paclitaxel) are the most in question |
| High doses | Large cumulative doses increase risk |
| Advanced age | Identified as a risk factor in consensus work |
| Molecule combinations | Some combinations (docetaxel-cyclophosphamide, TCHP) have the highest levels |
Please note: after chemotherapy, certain hormonal therapies can also maintain or worsen alopecia. The consensus also distinguishes persistent alopecia linked to chemotherapy from that induced by hormonal therapy, which occurs after complete regrowth.
Recognize PACIA: quand consulter
Distinguishing simply slow regrowth from PACIA is not always easy for the patient. A few guidelines help you know when to seek specialist advice.
- The deadline. Absent or clearly insufficient regrowth beyond six months after the end of treatment is the central criterion.
- L'aspect. Diffuse thinning, persistent sparse areas, hair that does not densify over the months.
- Vers qui se tourner. A dermatologist for the diagnosis – who can rely on an examination of the scalp, or even a biopsy – and a trained professional to support the hair field.
Consulting early allows you to assess the situation and consider appropriate treatment without waiting for additional months to pass.
- The central criterion is insufficient regrowth beyond six months.
- The diagnosis is made by the dermatologist.
- Consulting early expands the possibilities of care.
Act early: the window that counts
Faced with PACIA, one principle is essential: the moment when we act counts as much as what we do. The period immediately following the end of chemotherapy is a critical window — this is where the follicle attempts to restart, on a scalp that is still inflamed and weakened. Leaving this degraded terrain means asking weakened follicles to leave again in poor conditions.
Restore the ground from the last session
This is the whole meaning of the RENASCOR Laboratory approach: we rebuild before stimulating. Concretely, this means intervening in the field as soon as you leave chemotherapy, without waiting for the weeks to pass and the scalp to settle into an unfavorable state. The REDACTIV 1 serum, an early reconstruction treatment of 99% natural origin, is formulated precisely for this window: its application can start the day after the last session. It aims to soothe perifollicular inflammation, restore barrier function and reestablish a favorable follicular environment, at the exact moment when the follicle needs it most. Discover REDACTIV 1.
Acting early in the field does not guarantee to avoid a PACIA — no care can promise this, and an installed PACIA is a matter of medical advice. But providing the follicle with the best possible conditions from the start, rather than allowing a degraded terrain to set in, is the most consistent strategy with what is known about regrowth.
Prevention during treatment
Upstream, during chemotherapy, the 2025 expert consensus mentions the cooling helmet as a means of limiting exposure of follicles. Its effectiveness varies depending on the protocols and is discussed with the healthcare team.
Support for an installed PACIA
Once the PACIA has been established, treatment is a medical matter and is discussed with a dermatologist. Different approaches are studied; the data remains under construction and any support must be assessed individually.
- The window following the last session is decisive for the hair field.
- REDACTIV 1 is formulated for this early phase and can be started the day after the last chemo.
- Acting early provides the follicle with better conditions, without guaranteeing to avoid PACIA.
- A PACIA installed requires medical advice.
Frequently asked questions
Qu'est-ce que la PACIA exactement ?
It is a non-scarring alopecia that persists more than six months after the end of chemotherapy, with absent or incomplete regrowth. This definition is the subject of an international expert consensus published in 2025.
Is PACIA common?
More than we thought. A three-year cohort study reported incomplete regrowth in 39.5% of patients at six months. Taxane-based protocols have the highest rates, up to 52% for certain combinations.
Pourquoi les cheveux ne repoussent-ils pas ?
The mechanism adopted involves a depletion or destruction of follicle stem cells after chemotherapy. When this reservoir is depleted, the follicle loses all or part of its ability to produce new hair.
Which treatments present the most risk?
Protocols based on taxanes (docetaxel, paclitaxel), especially at high doses and in combination (docetaxel-cyclophosphamide, TCHP). Advanced age is also a risk factor.
Que faire si je pense avoir une PACIA ?
Consult a dermatologist for a diagnosis, ideally without waiting too long. A trained professional can support the care of the hair area in addition to medical advice.
Can we reduce the risk or take preventive action?
Two levers exist. During cures, the consensus of experts mentions the cooling helmet to limit the exposure of the follicles, with variable effectiveness. At the end of the treatment, restoring the hair surface offers the follicle better conditions for regrowth: this is the logic “we rebuild before stimulating”, for which the REDACTIV 1 serum is formulated and can be applied the day after the last session. Acting early does not guarantee avoiding a PACIA, but offers the best possible conditions.
This guide is published by the Laboratoire RENASCOR Paris, a French cosmeceutical laboratory specializing in hair reactivation and reconstruction since 2017, and its founder Stéphane Paulet. Our approach is based on a principle: we rebuild before stimulating. Discover our scientific approach and our sources.
Pour aller plus loin
This page is for information only. It does not replace medical advice and does not constitute an individual promise of results. PACIA requires medical diagnosis and care.