Why Vitiligo Repigments From the Hair Follicle Outward, and What That Means for Your Treatment Timeline

If you have started phototherapy or a topical treatment for vitiligo, your dermatologist may have told you to watch for small brown dots appearing inside your white patches. Many patients find these dots alarming at first. They look irregular, speckled, almost like a rash. In reality, those dots are the single most reliable early sign that treatment is doing its job, and understanding why requires a short trip into the anatomy of the hair follicle.

The reservoir hiding below the surface

In vitiligo, the immune system targets melanocytes, the pigment-producing cells that live in the bottom layer of the epidermis. When those cells are destroyed, the skin above them turns white. But the epidermis is not the only place melanocytes exist. Deep in the hair follicle, in a region called the bulge, sits a population of melanocyte stem cells. These cells are immature, they do not actively produce pigment, and, critically, they express far fewer of the surface proteins that the immune system uses to recognize and attack mature melanocytes. In many patients, this makes the bulge a relatively protected reservoir even while the surface melanocytes are wiped out.

When treatment calms the immune attack, whether through narrowband UVB, topical corticosteroids, calcineurin inhibitors, or the newer JAK inhibitors, these stem cells can activate. They divide, and their daughter cells migrate up the follicle to the skin surface, then spread outward from the follicular opening like ink from a dropped pen. Each hair follicle becomes a tiny island of returning pigment. That is the speckled pattern clinicians call perifollicular repigmentation, and it is why the dots appear centered on hairs.

Why location on the body matters so much

This mechanism explains one of the most consistent and frustrating patterns in vitiligo care: the face and neck respond faster than the hands and feet. Facial skin is densely packed with fine vellus hair follicles, each one a potential pigment source. The knuckles, fingertips, palms, soles, and bony prominences like ankles have few or no follicles. With little or no stem cell reservoir nearby, those areas depend on melanocytes slowly migrating in from the edges of the patch, a much less efficient process called marginal repigmentation. Studies of phototherapy response consistently show facial lesions repigmenting at substantially higher rates than acral lesions, meaning hands and feet, over the same treatment period.

Hair color within the patch is another prognostic clue. If the hairs growing inside a white patch are still dark, the follicular melanocyte lineage is likely intact, and the odds of repigmentation are meaningfully better. If the hairs themselves have turned white, a condition called leukotrichia, the reservoir in those follicles may already be depleted. Leukotrichia does not make repigmentation impossible, since neighboring follicles and lesion margins can still contribute, but it does temper expectations, and it is one reason clinicians examine hair color, sometimes with a dermatoscope, before predicting outcomes.

How to read your own progress honestly

Perifollicular repigmentation is slow by design. Stem cells must activate, proliferate, migrate up a follicle, and then expand laterally across the surface, and each of those steps takes weeks. Most phototherapy protocols expect the first visible dots somewhere between 8 and 12 weeks of consistent treatment, with meaningful coverage often requiring 6 to 12 months. The dots enlarge gradually and eventually merge. A patch that looks speckled and uneven at month four is often on its way to looking uniform at month ten.

Two practical takeaways follow from the biology. First, do not judge a treatment as failed before roughly three months of consistent use, because the cellular machinery simply has not had time to produce visible results. Second, if a patch on a low-follicle area like the fingers shows no response after many months, that is not a personal failure or a sign the diagnosis is wrong. It reflects reservoir anatomy, and it is precisely why surgical options such as melanocyte-keratinocyte transplantation exist for stable vitiligo in those locations: they physically deliver new melanocytes to areas that lack a natural supply.

One caution worth stating plainly: repigmentation requires that the autoimmune attack be controlled first. Stimulating pigment return into skin where the immune assault is still active is like refilling a leaking bucket. This is why combination approaches, an anti-inflammatory agent plus a repigmentation stimulus such as light, tend to outperform either alone in clinical studies, and why stability of the disease is assessed before any surgical grafting.

So if you spot brown freckles blooming inside a white patch, photograph them, date the photo, and keep going. Those dots are stem cells doing exactly what the treatment asked of them.

Related reading: Vitiligo: what it is and how it is treated.

Further reading: The immunology of vitiligo (Nat Rev Immunol 2026); Vitiligo (Ugeskr Laeger 2025); Comorbidities in Patients with Vitiligo: A Systematic Review and Meta-Analysis (J Invest Dermatol 2023).