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Trichomycosis axillaris

Author: Vanessa Ngan, Staff Writer, 2003. Updated by Dr Jannet Gomez, Postgraduate Student in Clinical Dermatology, Queen Mary University London, United Kingdom, April 2016.

Table of contents

What is trichomycosis axillaris?

Trichomycosis axillaris is a superficial bacterial infection of underarm hair. The disease is characterised by yellow, black or red granular nodules or concretions that stick to the hair shaft.  It can also affect pubic hair (when it is called trichomycosis pubis), scrotal hair, and intergluteal hair.

The name is misleading because "trichomycosis" is bacterial in origin rather than a fungal infection.

Trichomycosis axillaris

What causes trichomycosis axillaris?

Trichomycosis axillaris is caused by the overgrowth of Corynebacterium (Corynebacterium tenuis, C propinguum, C flavescens) and Serratia marcescens. The concretions consist of tightly packed bacteria. The bacteria proliferate in moist areas of the body, thus mainly affect underarm hairs, and to a lesser extent, pubic hair.

The bacteria cause malodour due to the metabolisation of testosterone in sweat into smelly compounds.  

Who gets trichomycosis axillaris?

Trichomycosis axillaris occurs in males and females of all races in temperate and tropical climates. It appears to be more common in men than women but this is because many women shave their underarm hair.

Contributing factors include:

  • Humidity and warmth
  • Crowded conditions
  • Poor hygiene
  • Hyperhidrosis
  • Obesity  

What are the clinical features of trichomycosis axillaris?

Trichomycosis axillaris is symptomless and often ignored. Signs include:

  • Sweaty, smelly armpits 
  • 1–2 mm yellow, red or black concretions encircling the hair shaft, which make the hair appear beaded or thicker. Yellow concretions are the most common, whilst red and black are found  in tropical climates 
  • Sweat is also discoloured yellow, red or black, and may stain clothing   
  • Hair loss is rare, and is due to bacteria invadind and destroying the hair shaft 

The corynebacterial triad is the occurrence of erythrasma, trichomycosis axillaris, and pitted keratolysis in a single individual.

What are the complications of trichomycosis axillaris?

Trichomycosis axillaris is a benign condition that does not have any complications. 

How is trichomycosis axillaris diagnosed?

  • Trichomycosis axillaris is mostly diagnosed by its clinical appearance.
  • Wood lamp examination shows pale-yellow fluorescence.    
  • Potassium hydroxide preparation and Gram staining can identify the bacteria. 

The condition may resemble pubic lice (pediculosis) and Trichosporon aselie infections.

What is the treatment of trichomycosis axillaris?

The fastest way to get rid of trichomycosis axillaris is to clip the affected hairs or shave the area

Effective topical antibacterial preparations include clindamycinerythromycin and fusidic acidClotrimazole powder is also curative.

How can trichomycosis axillaris be prevented?

Recurrences of trichomycosis axillaris are prevented by keeping the underarm dry and clean.

  • Antiperspirants with aluminium chloride reduce sweating 
  • Antiseptics such as benzoyl peroxide gel or wash reduce bacterial colonisation  



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