Pityriasis versicolor

Meet the patient

A 22-year-old man comes back from a fortnight in Goa worried that the skin across his chest and shoulders has 'turned whiter than the rest of me'. The patches are faintly pink, merge into one another across his upper back, and carry a dust of fine scale he only notices when he scrapes the edge with a fingernail. He has rubbed an over-the-counter bleaching cream on for two weeks with no change, and is now convinced it is spreading.[1][2]

Two exam questions are now live, and the whole topic exists to answer them: is this fungus, or is it vitiligo? and why has the colour not come back? Hold those two and every section below slots into place.[1]

One commensal, two phases — the switch that makes the disease

The cause is not an invader but a turncoat resident of the patient's own skin. Malassezia — formerly Pityrosporum — is a lipophilic yeast that lives harmlessly in the stratum corneum until the microenvironment turns hostile in its favour. These organisms are obligate lipophiles: they cannot synthesise their own fatty acids, so they colonise where sebaceous glands are busiest — the chest, back, shoulders, neck, and proximal arms.[1][3]

That lipid hunger is the entire explanation for the adolescence-and-sebum predilection. Malassezia takes hold only after puberty switches the sebaceous glands on; the disease peaks in the teens and twenties, flourishes in heat and humidity, and loves an oily, sweaty, occluded trunk. Risk factors to recite in one breath: heat and humidity, hyperhidrosis, occlusive clothing, oily skin, adolescence, immunosuppression, Cushing syndrome and corticosteroid use, and malnutrition — each one feeds the yeast lipid or tips the immune balance toward it.[1][2][3]

The single event that creates a lesion is the switch from the round commensal yeast form to the filamentous mycelial form. Heat, humidity, hyperhidrosis, seborrhoea, immunosuppression, and corticosteroids tilt the microenvironment; the yeast elongates into hyphae that invade the stratum corneum, and the scaly macules appear. The fine, bran-like scale you scrape off is the hyphal mass itself.[3]

The species the examiner wants named is M. globosa. Molecular typing across Iranian, Greek, Turkish, and Northern Iranian cohorts consistently recovers M. globosa from lesional skin — and, tellingly, its mycelial form is found almost exclusively in lesions while the yeast form dominates on the healthy skin of the same patient. That single observation is the molecular proof of the yeast-to-hypha switch.[4][5][6][7]

Why the same yeast makes some skin lighter and some darker. M. globosa and M. furfur metabolise tryptophan into azelaic acid, a nine-carbon dicarboxylic acid that competitively inhibits tyrosinase and blocks melanosome transfer to keratinocytes — the mechanism of hypopigmentation. Hyperpigmented lesions reflect inflammation and increased melanin transfer, not a different organism. M. furfur dominates in tropical settings and in hyperpigmented disease; M. sympodialis is the commonest commensal on healthy adult skin.[1][8]

'Spaghetti and meatballs' — the bedside tests that settle it

Two cheap bedside tests confirm pityriasis versicolor in under a minute, and a quiet third is gaining ground — none needs a laboratory turnaround.[1]

The potassium hydroxide mount is the confirmatory test. Scrape the active edge onto a slide, add 10 percent KOH, and read the pathognomonic 'spaghetti and meatballs' — short curved hyphae (the spaghetti) tangled with clusters of round yeast cells (the meatballs). Chicago Sky Blue or another contrast stain sharpens the image. The picture is unforgettable precisely because the metaphor is exact.[1][3]

Wood's lamp turns the diagnosis fluorescent. Active lesions glow pale yellow, yellow-green, or coppery-gold under Wood's lamp, courtesy of pityrialactone, a water-soluble tryptophan-derived fluorochrome the yeast secretes. Two honest caveats: the chromophore washes off after bathing or recent antifungal shampoo, so a negative lamp never excludes the disease.[8][1]

Dermoscopy is the quiet third test. Fine white scale settling into the skin furrows produces a 'wire-fence' or 'fish-net' pattern, with a double-edged scale when the skin is stretched and non-uniform pigmentation in the background — a useful non-invasive read when scraping is undesirable, as on a child's face.[9]

Culture on lipid-supplemented media such as modified Dixon's agar, and PCR-based speciation of the internal transcribed spacer region, are research and epidemiology tools — reach for them only when disease is recalcitrant, recurrent, or unexpectedly hyperpigmented.[5][7]

Vitiligo, pityriasis alba, or versicolor? — the scale-plus-KOH fork

This is the differential that loses marks, because the three pale eruptions look alike in a photograph and utterly different at the bedside. The fork is decided by scale and by KOH, in that order.[1][9]

The one-line discriminator: scale that scrapes off, plus spaghetti-and-meatballs on KOH, equals pityriasis versicolor. Vitiligo is depigmented — chalk-white, completely melanin-free, with no scale at all; pityriasis versicolor is merely hypo- or hyperpigmented, off-white or tan, and the fine scale lifts off. Pityriasis alba sits between them: a poorly defined, faintly scaly patch on the cheeks of an atopic child, KOH-negative.[1]

The broader mimic list, one discriminator each: tinea corporis (annular lesion with an active scaly border; KOH shows hyphae without the yeast clusters); seborrhoeic dermatitis (greasy yellow scale in the nasolabial folds and scalp — the same yeast, a different morphology); erythrasma (coral-red Wood's lamp fluorescence from Corynebacterium); pityriasis rosea (herald patch and Christmas-tree distribution, KOH-negative); and secondary syphilis (coppery papules on the palms and soles, serology positive).[1][5]

Bran and changing colour — the two words every examiner rewards

The name is two etymology clues, and both still teach. Pityriasis comes from the Greek pityron, meaning 'bran' — it names the fine, bran-like scale that is the disease's signature, the dust that lifts off when you scrape. Versicolor is Latin for 'changing colour', capturing how the same eruption looks pale on one patient and tan on the next.[1][3]

The older name tinea versicolor is wrong twice over: Malassezia is a yeast, not a dermatophyte, so 'tinea' misleads; and the pigmentation is altered, not uniformly coloured. Say 'pityriasis versicolor' in the viva and you have already sounded like a dermatologist.[1]

How common, and who — the sebum-and-sweat predilection

Pityriasis versicolor is among the commonest superficial mycoses worldwide, and its prevalence tracks climate and sebum almost exactly.[1]

A 2022 United States commercial-insurance analysis of 32,679 cases put the incidence at 2.8 per 1,000 person-years, peaking at 5.0 per 1,000 in 18 to 24-year-olds and in males — the age and sex profile of maximal sebaceous activity. In tropical, humid climates prevalence climbs to 40 to 50 percent of some populations; in temperate zones it sits near 0.5 to 4 percent.[2]

Infants are the exception that proves the sebum rule. A 2025 Chinese cohort of 415 children found that 35.4 percent were under six months old and the face was the most frequently involved site, at 65.3 percent, with hypopigmented disease in 96.9 percent. Facial and infantile PV is now well recognised, most likely reflecting close maternal contact before the infant's own sebaceous glands are active.[14][15]

Topical first, oral second — the treatment ladder

Topical therapy is first-line for limited and moderate disease; oral azoles are reserved for extensive, recalcitrant, or recurrent disease. A 2024 meta-analysis found no significant difference in clinical cure between topical azoles and keratolytic agents such as selenium sulphide, though the evidence base is modest.[13]

Three rules decide whether a topical works at all: apply it widely from the jawline down — subclinical carriage is the rule, not the exception; leave it in contact for the full 5 to 10 minutes before rinsing; and continue long enough to clear the reservoir. Skip any one and the patient 'fails' a perfectly good drug.[1][11]

A small head-to-head of 40 patients reported 95 percent clinical cure with 2 percent ketoconazole shampoo versus 85 percent with 2.5 percent selenium sulphide after three weekly applications — a difference that was not statistically significant, so either is a defensible first choice.[16]

When the topicals are not enough — itraconazole and fluconazole

Reserve systemic therapy for disease covering more than 20 percent of body surface, for recalcitrant disease, or for frequent relapse. The 2014 systematic review of 57 trials fixed the evidence-based doses examiners quote.[12]

Two oral drugs you must not reach for. Oral ketoconazole is no longer recommended for any superficial mycosis — the 2013 to 2014 FDA and EMA hepatotoxicity warnings and the adrenal-insufficiency signal ended its systemic use. Oral terbinafine does not work for Malassezia, because the organism does not depend on squalene epoxidase for its ergosterol. Name both exclusions and you separate yourself from the candidate who reaches for the familiar antifungal.[10][12]

Before any oral azole, check liver function, drug interactions, and pregnancy status. Topical agents — ketoconazole 2 percent, selenium sulphide 2.5 percent, and ciclopirox 1 percent — are the safe choices in pregnancy and breastfeeding; reserve oral azoles for exceptional cases with specialist input.[12]

The trap that fills the follow-up clinic — colour lags cure

Recurrence is the rule — maintenance is the answer

Because Malassezia never leaves the skin, recurrence reaches 60 to 80 percent within a year without maintenance. The disease is benign but relapses readily in warm, humid climates or with ongoing risk factors. Offer prophylaxis to anyone with two or more episodes a year: ketoconazole 2 percent or selenium sulphide 2.5 percent shampoo applied to the trunk for 10 minutes, once or twice monthly, and, for the frequent relapser, oral itraconazole 200 mg twice daily for one day each month.[3][16]

Special sites in one breath. For facial and infantile PV, prefer a gentle topical imidazole cream over a shampoo, which irritates the face; infantile hypopigmented PV has responded to 1 percent clotrimazole lotion twice daily for four weeks in reported cases. The immunocompromised host — HIV, transplant, systemic corticosteroids, biologics — gets more extensive and refractory disease; treat aggressively and involve the specialist early.[1][15]

The numbers you own before the viva

The mnemonic, and the mantra

The mantra: scrape the scale, see the spaghetti, shampoo the skin — the yeast dies fast, the colour returns slow.[1][3]

Ward-round test — three stems