biology

Tinea nigra

Tinea nigra is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Tinea nigra rather than just read about it. In short: Tinea nigra, also known as superficial phaeohyphomycosis and Tinea nigra palmaris et plantaris, is a superficial fungal infection, a type of phaeohyphomycosis rather than a tinea, that causes usually a single 1–5 cm dark brown-black, non-scaly, flat, painless patch on the palms of the hands and the soles of the feet of healthy people. There may be multiple spots.

Key takeaways

Tinea nigra belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Tinea nigra to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Tinea nigra from memory before moving on to harder problems.

Reference excerpt

Tinea nigra, also known as superficial phaeohyphomycosis and Tinea nigra palmaris et plantaris, is a superficial fungal infection, a type of phaeohyphomycosis rather than a tinea, that causes usually a single 1–5 cm dark brown-black, non-scaly, flat, painless patch on the palms of the hands and the soles of the feet of healthy people. There may be multiple spots. The macules occasionally extend to the fingers, toes, and nails, and may be reported on the chest, neck, or genital area. Tinea nigra infections can present with multiple macules that can be mottled or velvety in appearance, and may be oval or irregular in shape. The macules can be anywhere from a few mm to several cm in size. Most cases are caused by Hortaea werneckii, a pigmented fungus, which is a dark yeast found in sewage, soil, rotting vegetation and wood and in places with a high salt content such as moldy salted fish and on beaches, where contact with sand may result in transmission. Infection is by direct contact and the fungus enters and remains in the outer dead layer of skin with little or no skin inflammation. The infection does not invade deeper tissues. Diagnosis is by visualisation, dermoscopy, and microscopy and culture of skin scrapings. Differential diagnosis includes Addison's disease, syphilis, pinta, yaws, melanoma, lentigines, lichen planus of the palms, and junctional melanocytes nevus. Treatment is with topical Whitfield's ointment or salicylic acid ointment. Topical antifungals or oral itraconazole are other options. Scraping the lesion can be curative. Prevention is by general hygiene measures. It is uncommon. It generally occurs in tropical and subtropical countries of Central and South America, the Caribbean, Europe, South East Asia, Australia and the Far East. The disease was first described by Alexandre Cerqueira from Brazil in 1891. No cases in animals have been reported.

Signs and symptoms

Causes This infection is caused by the fungus formerly classified as Cladosporium werneckii, but more recently classified as Hortaea werneckii. The causative organism has also been described as Phaeoannellomyces werneckii. Tinea nigra is extremely superficial and can be removed from the skin by forceful scraping. It tends to appear in areas where eccrine sweat glands are highly concentrated. Infections generally start to appear on the skin around 2–7 weeks post inoculation. The ability of H. werneckii to tolerate high salt concentrations and acidic conditions allows it to flourish inside the stratum corneum. H. wernickii tends remain localized in one spot or region, and produces darkly-colored, brown macules on the skin due to the production of a melanin-like substance.

Diagnosis Diagnosis of tinea nigra is made based on microscopic examination of stratum corneum skin scrapings obtained by using a scalpel. The scrapings are mixed with potassium hydroxide (KOH). The KOH lyses the nonfungal debris. The skin scrapings are cultured on Sabouraud's agar at 25°C and allowed to grow for about a week. H. werneckii can generally be distinguished due to its two-celled yeast form and the presence of septate hyphae with thick, darkly pigmented walls.

Treatment Treatment consists of topical application of dandruff shampoo, which contains selenium sulfide, over the skin. Topical antifungal azoles such as ketoconazole, itraconazole, and miconazole may also be used. Azoles are generally used twice daily for a two-week period. This is the same treatment plan for tinea or pityriasis versicolor. Other treatment methods include the use of epidermal tape stripping, undecylenic acid, and other topical agents such as ciclopirox. Once a tinea nigra infection has been eradicated from the host, it is not likely to reoccur.

Epidemiology Tinea nigra is commonly found in Africa, Asia, Central America, and South America. It is typically not found in the United States or Europe, although cases have been documented in the Southeastern United States. People of all ages can be infected; however, it is generally more apparent in children and younger adults. Females are three times more likely than males to become infected.

Illustrations

Worked examples

Example 1 — a first encounter with Tinea nigra

Start with the simplest possible case. Write down what Tinea nigra claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Tinea nigra before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Tinea nigra ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Tinea nigra

In research: Tinea nigra appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Tinea nigra in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Tinea nigra is common in secondary-school and first-year university syllabi. It links to neighbouring topics Animal fungal diseases, Mycosis-related cutaneous conditions, so understanding it makes those chapters shorter.
In everyday life: Look for Tinea nigra outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Tinea nigra” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Tinea nigra in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Tinea nigra means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Tinea nigra out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Tinea nigra in simple terms?

Why does Tinea nigra matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Tinea nigra?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Tinea nigra.