Trichomycosis axillaris is a superficial bacterial colonization of the hair shafts in sweat gland

Sweat gland

Sweat glands, or sudoriferous glands, are small tubular structures of the skin that produce sweat. There are two kinds of sweat glands:...

–bearing areas, such as the armpits and the pubic area. It is a trivial disease of worldwide occurrence that is believed to be caused by the genus Corynebacteria (mostly Corynebacterium tenuis).

Presentation

It is characterised by cruddy yellow, orange, black or red granular nodules, coatings, concretions that stick to the hair shaft. Usually the condition is symptomless and all that is noticed are sweaty, smelly armpits. Hair shafts may also swell appearing more noticeable after bathing. It results from corynebacterial overgrowth on hair shafts in moist regions of the body and predominantly affects axillary hair (under arms), and to a lesser extent, pubic hair (trichomycosis pubis).
It is caused by several species of the gram-positive diphtheroid Corynebacterium, not by a fungus as the name may imply.

Treatment

The fastest method of treatment is to shave the affected hair.
Daily cleansing with soap and water and application of benzoyl peroxide

Benzoyl peroxide

Benzoyl peroxide is an organic compound in the peroxide family. It consists of two benzoyl groups bridged by a peroxide link. Its structural formula is [C6H5C]2O2. It is one of the most important organic peroxides in terms of applications and the scale of its production...

 (wash or gel formulations) cures the infection. Regular use of antiperspirants aids in prevention by reducing axillary hyperhidrosis (i.e. it staying moist). Topical antibiotic preparations such as erythromycin

Erythromycin

Erythromycin is a macrolide antibiotic that has an antimicrobial spectrum similar to or slightly wider than that of penicillin, and is often used for people who have an allergy to penicillins. For respiratory tract infections, it has better coverage of atypical organisms, including mycoplasma and...

or clindamycin is occasionally required to eliminate the infection. "Drying" powders may assist treatment.