Tinea nigra affects the skin of the palm and/or sole with persistent slowly growing brown or black patches. They are slightly scaly and do not itch or sting. Tinea nigra is most common in tropical regions and often infects those with a tendency to excessive sweating (hyperhidrosis).
Tinea nigra is due to infection with a brown mould, Exophiala phaeoannellomyces. This mould usually inhabits soil.
The organism's other names include:
- Hortaea werneckii
- Phaeoannellomyces werneckii
- Exophiala werneckii
- Cladosporium werneckii
The infection is sometimes confused with other skin conditions such as:
- Benign moles (naevi)
- Pigmentation arising after a dermatitis or other skin inflammation
Scrapings taken from the edge of the scaly lesion show mycelium (a group of branched filaments or hyphae). The hyphae can be clear in colour, yellow or brown and are septate (this means they are divided into compartments by thick walls).
Culture grows black colonies of Phaeoannellomyces wernekii within a week.
The diagnosis may also be made on skin biopsy because of characteristic histopathological features of tinea nigra.
Treatment of tinea nigra
Tinea nigra usually clears with topical antifungal applied for 2 -4 weeks.