A reader sent me photos of her upper back. She had been treating what she thought was post-inflammatory hyperpigmentation from old body acne for fourteen months. Azelaic acid, then a hydroquinone cream her cousin had brought from abroad, then a series of glycolic body lotions, then a retinoid body cream her dermatologist had reluctantly prescribed.
Nothing had moved. The patches were still there. Some were lighter than her surrounding skin and some were darker. They were slightly scaly when she scratched them, which she had attributed to dry winter air.
I asked her whether her dermatologist had used a Wood’s lamp. She did not know what that was.
This is the diagnostic shortcut I find myself recommending most often when readers describe pigmentary patches that have ignored every standard treatment. The condition involved is tinea versicolor, also called pityriasis versicolor, and it is genuinely common, frequently misdiagnosed, and treatable with cheap drugstore antifungals once you know what you are looking at.
What tinea versicolor is
Tinea versicolor is a superficial skin infection caused by the yeast Malassezia, most commonly the species Malassezia globosa and Malassezia furfur. The yeast is part of the normal skin flora in most adults. In some people, under conditions of heat, humidity, occlusion, or sebum production, it overgrows and produces patches of altered pigmentation.
The patches are typically on the chest, upper back, shoulders, neck, and sometimes the upper arms and jawline. They can be lighter than surrounding skin (hypopigmented) or darker (hyperpigmented), and they often have a fine, almost imperceptible scale that becomes visible when you scratch the area lightly.
The mechanism for the pigment change is biochemical, not melanin synthesis in the usual sense. The yeast produces azelaic acid and several other dicarboxylic acids as metabolic byproducts. These compounds inhibit tyrosinase in nearby melanocytes, which is why the affected areas often appear lighter on tanned skin. They can also trigger a local inflammatory response that produces a different pigmentary pattern, which is why some patches appear darker, especially in Fitzpatrick IV-VI skin.
The clinical implication is enormous. Standard pigmentation treatments aimed at melanocyte regulation, including hydroquinone, retinoids, tranexamic acid, and most chemical peels, do almost nothing for tinea versicolor because they are addressing the wrong target. The melanocytes are not behaving abnormally on their own. They are responding to a yeast that needs to be cleared first.
What the studies actually show
Hu and Bigby published a clinical diagnostic review that I still send to readers (Hu & Bigby, Dermatol Clin 2018, PMID: 30009909). Their walkthrough of the differential is the cleanest I have read, and they emphasised that visual diagnosis alone misses or misidentifies tinea versicolor frequently, especially in higher Fitzpatrick types where the colour contrast can mimic post-inflammatory hyperpigmentation.
The two cheap, reliable diagnostic tools they recommend are the Wood’s lamp and the potassium hydroxide preparation.
A Wood’s lamp is a long-wavelength UV light, around 365 nm, used in darkened conditions. Tinea versicolor patches characteristically fluoresce yellow-green or coppery-orange under the lamp. The fluorescence is produced by metabolic products of the Malassezia yeast and is not present in melanin-based pigmentation, post-inflammatory hyperpigmentation, vitiligo, or most other common pigmentary conditions. The lamp itself costs around 15 to 30 dollars in a consumer version, and dermatologists have higher-quality versions in their clinics.
The KOH prep is more sensitive but requires a microscope. The clinician scrapes a small amount of the affected scale, places it on a slide with potassium hydroxide, and looks for the “spaghetti and meatballs” pattern of yeast hyphae and spores characteristic of Malassezia. This is what should happen at a dermatology visit if the diagnosis is uncertain.
Gupta and colleagues published a systematic review of treatment options that has aged reasonably well (Gupta et al., J Am Acad Dermatol 2002, PMID: 12100024). The first-line treatments are topical antifungals. Ketoconazole 2 percent shampoo applied to the affected area, left for 5 to 10 minutes, then rinsed, used daily for two weeks. Selenium sulphide 2.5 percent lotion used similarly. Zinc pyrithione shampoo as a slower but equally effective alternative.
The newer additions are topical azoles like ciclopirox cream and tioconazole solution. Oral antifungals like fluconazole or itraconazole are reserved for extensive or recurrent cases and require liver function monitoring.
The pigment change itself, the lightened or darkened patches, does not resolve immediately when the yeast clears. The patches can take three to six months to repigment to normal as the melanocytes resume usual function. This is the part that frustrates readers who clear the active infection and still see the patches in the mirror.
The diagnostic test you can run
The Wood’s lamp test is the most accessible version of this.
Buy a long-wavelength UV lamp in the 365 nm range. The cheap blacklights at hardware stores are often shorter-wavelength and less useful. Look for a Wood’s lamp specifically intended for dermatologic use.
Take the lamp into a fully dark room. Hold it about 10 to 15 centimetres from the affected skin. The lamp needs to be the only light source, so eyes should be adapted to the darkness for at least a minute first.
Look for fluorescence. Tinea versicolor patches will produce a yellow-green or coppery-orange glow. Post-inflammatory hyperpigmentation and melasma do not fluoresce. Vitiligo patches fluoresce bright milky-white. Some sebaceous and acne-related conditions produce a coral-red fluorescence from Cutibacterium acnes porphyrins, especially on the nose.
If you see the yellow-green pattern, your patches are most likely tinea versicolor and your treatment plan needs to change. If you see nothing, the patches are more likely pigmentary in the conventional sense and the standard treatments you have already tried are at least targeting the right mechanism (even if they have not worked yet).
The home Wood’s lamp is not a perfect diagnostic. It produces false negatives in roughly 30 to 40 percent of tinea versicolor cases, especially after the patient has recently bathed (the fluorescing metabolites can be washed off temporarily). It can also miss subtle cases. The high-quality clinical lamps in dermatology offices produce more consistent results.
For uncertain cases, the right answer is a dermatology visit with KOH microscopy. The visit is brief, the test is cheap, and the diagnosis is definitive.
The contrarian part
Tinea versicolor is genuinely common. It is one of the most common dermatologic conditions in humid climates and affects somewhere between 1 and 50 percent of adults depending on the region, season, and population studied.
It is also genuinely under-diagnosed in Western dermatology, partly because the patches are easy to mistake for cosmetic pigmentation and partly because patients often present at the cosmetic dermatology end of practice rather than the medical end. A patient who walks into an aesthetic clinic asking about her uneven chest is more likely to be offered a chemical peel than to be examined under a Wood’s lamp.
The misdiagnosis pattern I have seen in reader emails is consistent. The patches appear in late teens or twenties, often after a humid summer or a period of heavy exercise. They are mistaken for sun damage or hormonal pigmentation. The patient is recommended brightening serums, peels, or retinoids. Nothing works. Years pass. By the time the diagnosis is corrected, the patient has often spent several hundred to several thousand dollars on the wrong category of product.
The contrarian recommendation is simple. If you have patchy pigmentation on the chest, back, shoulders, or neck that does not respond to a six-month course of azelaic acid, retinoid, or vitamin C, your next move should be a Wood’s lamp examination or a KOH prep, not another brightening serum.
The other contrarian point is that tinea versicolor is recurrent in most people. The Malassezia yeast remains part of normal skin flora and overgrows again under the same environmental conditions. A single treatment course clears the active infection. It does not change the underlying tendency. Maintenance therapy, usually a monthly ketoconazole shampoo wash, is what prevents relapse during humid months. The recurrence rate without maintenance is around 60 percent within two years in most series.
What I would tell my past self
Spend the 20 dollars on a Wood’s lamp before you spend another 100 on a brightening serum. The diagnostic is cheap and the implications are large.
If the lamp shows fluorescence, the treatment is a 12 dollar bottle of ketoconazole 2 percent shampoo applied as a leave-on for ten minutes, rinsed, repeated daily for two weeks. The repigmentation will take months. The active infection clears in days.
Do not assume the dermatologist used a Wood’s lamp unless they explicitly did. Many cosmetic-focused practitioners skip the step. Ask directly. If they have not, request it or get a KOH prep.
Plan for maintenance if the diagnosis is positive. A monthly ketoconazole shampoo wash during humid months reduces recurrence dramatically. Skipping maintenance is why the patches come back.
Be patient about the pigment. The patches you see after the yeast clears are the slow trail of melanocyte recovery, not residual infection. Sun exposure during the recovery period can amplify the contrast and slow the return to even pigmentation, so sunscreen on the affected area helps.
Frequently asked
How do I know if my patches are tinea versicolor or melasma?
Melasma is almost always on the face, especially the cheeks, forehead, and upper lip. It is symmetrical and does not fluoresce. Tinea versicolor is more often on the chest, back, and shoulders, has subtle scale, and fluoresces yellow-green under a Wood’s lamp.
Can tinea versicolor appear on the face?
Yes, especially along the hairline, jawline, and temples, where sebum production supports Malassezia overgrowth. It is less common on the face than on the trunk but not rare.
Why does it keep coming back after I treat it?
Malassezia is part of normal skin flora and re-establishes when treatment stops. Recurrence within one to two years is the norm, not the exception. Monthly maintenance washes during humid months reduce the rate substantially.
Is tinea versicolor contagious?
Not in the usual sense. The yeast is already present on most adult skin. Overgrowth depends on individual susceptibility, sebum production, humidity, and immune factors, not on transmission from one person to another in any clinically meaningful way.
Can I treat it with the same azelaic acid I use for hyperpigmentation?
Azelaic acid has some antifungal activity against Malassezia, but it is not the first-line treatment. Topical azole antifungals (ketoconazole, ciclopirox) clear the infection faster. Azelaic acid can be useful as a maintenance adjunct.
Related Elelaf tools
Hyperpigmentation type | Sebderm rosacea eczema decoder | Bump decoder | Face redness reset
Sources
- Hu SW, Bigby M. Pityriasis versicolor: a systematic review of interventions. Dermatol Clin 2018;36(3):209-218. PMID: 30009909.
- Gupta AK, et al. Pityriasis versicolor. J Am Acad Dermatol 2002;46(2):219-237. PMID: 12100024.
- Crespo-Erchiga V, Florencio VD. Malassezia yeasts and pityriasis versicolor. Curr Opin Infect Dis 2006;19(2):139-147. PMID: 16514338.
- Renati S, et al. Pityriasis versicolor: an updated review. Cutis 2015;96(1):51-56.