Trichomycosis Axillaris : Malodorous yellowish armpit hair

Synonym: Trichobateriosis axillaris, Bacterial trichonodosis, Trychomycosis palmellina

Definition: Asymptomatic superficial bacterial infection (mycosis is a misnomer because it is not a fungal infection) primarily of the axillary hairs (can also occur in pubic, perianal and scalp hair) caused by Corynebacterium sp.

Causative organism: Corynebacterium species particularly Corynebacterium flavescens

Mode of infection:

  1. Bacteria comes in contact with the hair shaft, and adhere to the surface, or the cuticle, of the hair, using a cement-like substance that is insoluble in water
  2. Micro-organism does not penetrate to the medulla’s cortex of the hair; instead, it only adheres strongly to the surface of the hair and develops slowly until it forms concretions around the hair shaft
  3. Encapsulated corynebacteria entrapped in a biofilm serve as the adhering mechanism, which possibly helps the organism to escape immunological attack by the host

Clinical variants:

  1. Trichomycosis flava (yellow)
  2. Trichomycosis rubra (red)
  3. Trichomycosis nigra (black)

Predisposing factors:

  1. Warm and humid climate
  2. Excessive sweating
  3. Inadequate hygiene
  4. Not shaving the area (hence, more common in male than female)
  5. Young adults
trichomycosis axillaris

Clinical features:

  1. Formation of concretions around the hair shaft:
    • Early: Invisible and only a slight thickening can be “felt” on palpation and later the bacterial masses remain isolated or independent (pediculosis-like)
    • Chronic: Concretions extend along the entire length of the hair until they form a sheath, causing the hair to thicken, turn a yellowish, red or black color, and become creamy, opaque and soft.
  2. Bromhidrosis (malodor)
  3. Hyperhidrosis (excessive sweating)
  4. May stain clothing

Wood’s lamp examination: Pale-yellow fluorescence

Dermoscopy: Yellowish-white masses with a waxy appearance, adherent to the hair (feather, brush or skewer sign); Concretions with the appearance of a rosary of crystalline stones; a flame-like pale yellowish adherent nodule (plume sign)

KOH examination: Mucoid sheath around hairs

Gram stain: Hair shafts colonized by gram-positive coccobacilli

Culture: A mixture of microorganisms may be identified: Corynebacterium sp. (white-yellow growth) and Serratia mascescens (red growth)


A. General measures:

  1. Adequate hygiene
  2. Shaving of the affected area for 2-3 weeks
  3. Control of hyperhidrosis

B. Cleansing methods: Use of sulfur soaps

C. Topical treatments:

  1. 3% sulfur
  2. 2% sodium hypochlorite
  3. 1% mercury chloride
  4. 5% Benzoyl peroxide
  5. Antibiotics: Fusidic acid, 2% Erythromycin, 1% Clindamycin
  6. Antimycotic agents: Naftifine, Some azole derivatives


  1. Bonifaz A, Váquez-González D, Fierro L, Araiza J, Ponce RM. Trichomycosis (trichobacteriosis): clinical and microbiological experience with 56 cases. Int J Trichology. 2013 Jan;5(1):12-6. doi: 10.4103/0974-7753.114704. PMID: 23960390; PMCID: PMC3746219.

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