Trichobacteriosis: Symptoms, Risk Factors, Causes, Diagnosis, Complications and Treatments

It is a superficial, asymptomatic infection generally caused by a coryneform-actinomycete bacterium called Corynebacterium tenuis.

Trichobacteriosis is a rare condition. This condition is also known as axillary trichomycosis. However, this name is incorrect because it is not a fungal infection but a superficial bacterial infection, so it should be called trichobacteriosis.

Patients generally do not seek medical attention because the condition is asymptomatic and causes no discomfort. However, when a careful and deliberate search is done in the clinical context, it tends to appear more frequently.

Axillary trichobacteriosis is often asymptomatic. However, patients may report sweaty and smelly armpits, and some may be aware of nodules or concretions in the axillary hairs.

Similar nodules can occur on the pubic hair (trichobacteriosis pubis). Discolored underarm sweat can stain clothing. A history of poor hygiene and axillary hyperhidrosis is often obtained.

Characteristic findings on physical examination and symptoms

Examining the axillary hairs reveals 1-2 mm yellow, red, or black granular nodules or concretions surrounding the hair shafts. This makes the hairs look embroidered.

These nodules are firmly attached to the hair shaft and are difficult to remove. The most common nodule color is yellow, although red and black are the most common colors in tropical climates.


The area may have associated with hyperhidrosis, and the sweat may turn yellow, red, or black. There is no brittleness or alopecia associated with the hair, and there is no underlying pigmentary change in the skin.

Similar concretions can be seen in pubic hair in a minority of cases (trichobacteriosis pubis). Other conditions related to corynebacteria can also be examined, including dimpled keratolysis and erythrasma (the so-called corynebacterial triad).

Other symptoms

  • Sweaty and smelly armpits.
  • Sweat stains on clothing.
  • The appearance of thick armpit hair.
  • Hair loss due to excess bacteria and destroyed hair shafts.

This condition is not contagious. However, you should seek treatment once you notice the symptoms. Trichomycosis can affect multiple areas at the same time. If you think your symptoms are getting worse, contact your doctor.

Expected results of diagnostic studies

Axillary trichobacteriosis is caused by several species of gram-positive corynebacteria. A potassium hydroxide (KOH) preparation, followed by a light microscopic examination, will show the causative bacteria in the concretions.

A Gram stain will also show thin purple bars under a light microscope. Examination of light or Wood’s lamp will show a dull yellow or whitish gray fluorescence.

Confirmation of diagnosis

The differential diagnosis of axillary trichobacteriosis includes hair casts, stone, pubic lice, and artifacts from deodorants, creams, soaps, or powders. Microscopy and Wood’s light examination help differentiate these conditions.

The capillary scales are amorphous in appearance and do not show bacteria. They are easily mobile along the hair shaft.

The white stone is a fungal infection that can affect armpit hair. It appears as white, cream, or brown nodules, which can easily be detached from the hair shaft. In addition, the KOH examination will reveal encapsulated arthroconidia or blastoconidia and not bacteria.

Pediculosis pubis (pubic lice, crabs) affects the pubic area, but axillary hairs can also be involved in some men. Nits, nymphs, and adult lice are identified with a magnifying glass and easily removed with tweezers.

Who is at risk of developing this disease?

Axillary trichomycosis is a common condition throughout the world. About 25% -30% of adult men are affected. Women are less likely to be affected because they commonly shave underarm hair.

Axillary hyperhidrosis and poor hygiene are the most critical risk factors. Hot climates and humidity are also risk factors.

What is the cause of the disease?


Axillary trichobacteriosis is caused by several species of aerobic gram-positive corynebacteria (mainly Corynebacterium tenuis) that colonize the axillary stems of the hair.

Moist areas rich in sweat glands, including the armpits (trichobacteriosis axilla) and the pubic region (trichobacteriosis pubiana), are preferred sites for these bacteria.


Trichomycosis axilla is a superficial bacterial infection of the axillary hair. Corynebacteria produce a cement-like substance, which facilitates bacterial adherence to hair.

Electron microscopy shows the destruction of the hair cuticle and superficial portions of the hair cortex. The musty odor is due to the ability of Corynebacteria to metabolize testosterone and other hormones found in apocrine sweat into various malodorous compounds.

Different types of Corynebacteria produce different pigments, including yellow (trichomycosis axillaries flavus), red (trichomycosis axillaries Rubra), and black (trichomycosis axillaries nigra).

Systemic Implications and complications

Axillary trichobacteriosis is a benign condition and is not associated with systemic abnormalities; however, it is essential to evaluate for Corynebacterium infections elsewhere in the body, including the pubic area (trichobacteriosis pubis), the feet (dimpled keratolysis), and intertriginous areas (erythrasma).

Treatment options

Trichobacteriosis is treatable. The infection can clear up in a few weeks with proper administration and good hygiene. Before applying any treatment method, you should shave the hair in the affected area.


After trichobacteriosis is diagnosed, doctors may prescribe topical antibiotics. Your doctor may prescribe clindamycin or erythromycin lotion. Apply these creams to the affected area twice daily for up to two weeks.

You may also receive benzoyl peroxide gel or lotion. These ointments can cause skin irritation.

If topical antibiotics do not work, your doctor might prescribe an erythromycin pill. You must take these supplements daily for up to two weeks.

If symptoms do not go away, talk to your doctor for more tests and different treatment recommendations.

Healthy hygiene

Proper hygiene can help remove bacteria from affected areas. This includes:

  • Wash the area every day with soap and water.
  • Use antiperspirant to reduce sweating and bacteria buildup.
  • Use talc-free drying powders like baby powder or Gold Bond to help reduce moisture.
  • Wash and dry clothes well after use.

The musty odor can linger on clothing, and patients should be reminded to wash or dry clothing properly.