Hypomelanosis explained: progressive macular hypomelanosis, the pale trunk patches that keep getting treated as fungus

Hypomelanosis is the medical word for skin that carries less melanin than it should. It is a description, not a diagnosis, and that is exactly why people end up confused. The term sits inside the names of several unrelated conditions, from the tiny white dots on aging shins to a rare birthmark pattern in infants. But when an adult in their twenties or thirties types the word into a search bar, it is usually because a dermatologist wrote one specific phrase on a visit summary: progressive macular hypomelanosis, often shortened to PMH.

The typical story we hear goes like this. Faint, pale, coin-sized spots appear on the back or stomach. They do not itch, flake or hurt. Someone says it is a fungus, an antifungal cream or shampoo is used for weeks, and nothing changes. Then a second round of antifungals. That loop is the reason this page exists.

The original element in this piece is a five-question self-check that sorts pale trunk patches into the three conditions most often confused with each other, followed by a plain accounting of how thin the treatment evidence really is. We have not seen these questions published together as one routing guide. Each question is drawn from how the condition is described in the clinical literature cited below; the sequence and the meaning we attach to each answer are assembled here. It does not replace an exam. It tells you what to ask for at the exam.

What hypomelanosis means, and the four conditions that carry the name

Progressive macular hypomelanosis is the common adult form. A 2007 overview from the Netherlands Institute for Pigment Disorders describes it as ill-defined, round, non-scaly pale spots on the trunk, often merging near the midline of the back and belly, rarely reaching the neck or upper arms, with no itch, pain or preceding rash (Relyveld et al., Am J Clin Dermatol 2007). It is seen worldwide, more often in young women and in people with darker skin from or living in tropical climates, and it tends to stay stable or creep slowly before often fading after mid life.

Idiopathic guttate hypomelanosis is the second: small, sharp, confetti-like white dots on the shins and forearms that accumulate with sun exposure and age. We cover it in detail in those little white spots on your arms and legs. Hypomelanosis of Ito and nevus depigmentosus are the other two, and both begin in infancy or early childhood. The first follows swirling streaks along developmental lines of the skin and is evaluated by pediatric specialists; the second is a single stable pale birthmark. If your patches arrived in adulthood on your trunk, neither of those is your answer.

Why progressive macular hypomelanosis gets mistaken for fungus

The usual misdiagnosis is tinea versicolor, a yeast overgrowth that also leaves pale patches on the chest and back in warm weather. The two look alike from a few feet away. The difference is biological. In 2004, the same Amsterdam group noticed that under a Wood's lamp in a dark room, PMH patches showed tiny red dots of fluorescence centered on the hair follicles, and normal skin did not. Biopsies from those patches found Cutibacterium acnes (then called Propionibacterium acnes), the same skin bacterium involved in acne, sitting in the follicle ducts; healthy skin from the same patients did not grow it (Westerhof et al., Arch Dermatol 2004). The leading theory is that certain strains release something that quietly slows pigment production around each follicle.

That is why antifungals fail. They are aimed at a yeast that is not there. A potassium hydroxide scraping, the quick microscope test for tinea versicolor, comes back negative in PMH, and that negative result is useful information rather than a dead end. Our explainer on how the Wood's lamp still settles these questions covers what the light shows and why it is cheap and quick.

The five-question self-check for pale trunk patches

Do this in good light, with a hand mirror for the back or a partner to help.

Question one, where are they? Patches clustered on the back, belly and sides, especially near the spine or navel, fit PMH or tinea versicolor. Small dots on the shins and outer forearms fit guttate hypomelanosis instead.

Question two, does anything come off? Stretch the skin of one patch between two fingers, or scrape it gently once with a fingernail. Fine, bran-like scale appearing on a patch points toward tinea versicolor. A patch that stays perfectly smooth points toward PMH.

Question three, are the edges sharp or soft? Tinea versicolor and vitiligo patches tend to have crisper borders. PMH patches fade into normal skin without a clear line, which is why people describe them as smudges.

Question four, how pale is pale? Chalk white suggests true pigment loss such as vitiligo, which deserves prompt evaluation. Off white or a shade lighter than your normal skin fits hypomelanosis.

Question five, what happened after antifungals? If a full course of a prescribed antifungal did nothing at all, that history itself raises the likelihood of PMH.

What the answers mean: smooth, soft edged, off white trunk patches that ignored antifungals form the classic PMH pattern. Bring that summary to the appointment and ask two things: a Wood's lamp exam looking for red follicular dots, and a potassium hydroxide scraping to rule out yeast. Those two tests, together, usually settle it in one visit.

What treatment looks like, and how much evidence stands behind it

Because the bacterial theory points to the follicle, treatment borrows from acne care. In a randomized left versus right body comparison of 45 patients, benzoyl peroxide 5% gel with clindamycin 1% lotion plus UVA light repigmented better than a steroid cream with the same light (Relyveld et al., J Am Acad Dermatol 2006). A small Brazilian placebo controlled trial of the same benzoyl peroxide and clindamycin combination with daily sun exposure reported meaningful improvement in 11 of 13 treated patients versus 2 of 10 on placebo, with more skin irritation in the treated group (Santos et al., An Bras Dermatol 2011). Narrowband UVB alone, given once or twice weekly, produced more than 90 percent repigmentation in 9 of 16 Korean patients who completed treatment, in a study without a control group (Kim et al., J Am Acad Dermatol 2012).

What the studies do not tell you

Add those trials up and the controlled evidence for treating progressive macular hypomelanosis rests on fewer than 90 people. No published trial compares the topical antibacterial approach directly against narrowband UVB, so nobody can tell you which to start with on evidence alone. Follow up in the best study ran about a year, which means recurrence after that is largely unmeasured, and patients do report patches returning in a later summer. Benzoyl peroxide also bleaches fabric, a practical cost the trials never discuss for a treatment applied to the whole back. And because the condition often fades after mid life on its own, doing nothing but sun protection and waiting is a legitimate choice the literature has never tested formally. The honest framing is that the cause is reasonably well supported and the best treatment is still an open question.

For the bigger picture of how these conditions fit together, start at our hypopigmentation overview. If pale patches keep coming back after one condition is treated, ask whether a second one was there all along; PMH and tinea versicolor can coexist on the same back. A clear diagnosis, not another tube of antifungal, is what ends the loop.

Further reading: Progressive macular hypomelanosis, DermNet.