Trichobacteriosis: A salute to the Shelleys

By Warren R. Heymann, MD, FAAD
Sept. 3, 2025
Vol. 7, No. 35

Indelible memories form in youth. I couldn’t wait to get my New York driver’s license — within a year of that milestone the 1973 oil embargo hit, and most drives were limited to the gas station to wait on interminable lines; at the pump I would request “unleaded” gasoline (leaded gas was banned in 1996). New Jersey is the only state where you cannot pump your tank — a gas station attendant must do this. Although I have been driving an electric car for 5 years, I still say that I need to fill it up rather than charge it. At gas stations with my wife’s car, sometimes I will inadvertently ask for unleaded gas, which (appropriately) elicits bizarre, quizzical looks from the attendant. I quickly correct myself, saying, “Never mind, just fill it with the low octane, thank you.”

The parable’s point is that what we learn early stays with us, even if new knowledge challenges old dogma. No one suggests that mycosis fungoides is anything other than a cutaneous T-cell lymphoma, yet the term persists. Murphy and Maiberger correctly assert that trichomycosis axillaris (TMA) is a misnomer because it is a superficial bacterial infection of the hair caused by Corynebacterium species instead of fungi. (1) Newer literature prefers the precise term trichobacteriosis (TB). This commentary will use both terms interchangeably.

Montes de Oca-Loyola et al. eloquently reviewed the history of TB. “Trichobacteriosis was first described by Paxton in 1869 in an article entitled ‘On a disease condition of the hairs of the axilla, probably of parasitic origin.’ Named for its similarity to Trichophyton tonsurans, Paxton thought that he had detected spores like those found in favus or tinea favosa but was unable to find the mycelial structures. Later, in 1927, Castellani observed that the flava variety was apparently caused by ‘a very thin fungus,’ with a bacillary appearance, which he named Nocardia tenuis, but he was unable to cultivate it. He attributed the rubra and nigra varieties to a symbiosis of this fungus with chromogenic cocci; a black pigment-producing cocci (Mycrococcus nigricans) in the nigra variety and red pigment-producing cocci in the rubra variety. In 1952, Crissey et al., after studying 100 consecutive cases in a University Hospital in Philadelphia, where 23 patients had clinical evidence of trichobacteriosis, identified that it was caused by a single diphtheroid, which they cultured and named C. tenuis.” (2)

“The surface of the human skin swarms, even as the surface of the planet Earth, with myriads of invisible bacteria. Over half of these are gram-positive pleomorphic aerobic rods. Although they belong to the genus Corynebacterium, they have blithely procreated in a bewildering variety of mongrel strains that virtually defy taxonomy by species. Only one member of the genus, Corynebacterium diphtheriae, the famous pathogen and first of the genus to be recognized, is an exception to this.” (3) (This quote is from Drs. Walter B. Shelley and E. Dorinda Shelley. Some have complimented my writing because I remind them of the Shelleys. I disagree — they are in a class of their own.) In a systematic review encompassing 365 TB patients, of whom 71 were cultured, Corynebacterium flavescens was most common, representing 80% (57/71). However, many of the reports included did not identify the etiological agent, which could represent a higher proportion. The rubra variety follows in frequency, and lastly, the nigra, with very few cases reported in the literature. (2)

TMA is most common in adults aged 20–50 years, with a higher prevalence in males, and is associated with factors such as localized hyperhidrosis, obesity, humid environments, and poor hygiene. Although most cases affect axillary hair, pubic and perianal hair may also rarely be involved. (3,4) TMA may be asymptomatic; some may experience bromhidrosis (body odor) or chromhidrosis (colored sweat). (1,4) Initially, the bacterial concretions are invisible, with only a perceived thickening of the hair on palpation. Subsequently, some masses form independently. As the infection becomes chronic, the concretions spread along the hair until they form sheaths, causing thickening of the hair. A biofilm around the bacteria helps the organism avoid the immune system. The bacteria adhere to the cuticle, allowing concretions to form, but do not enter the medulla. (4)

---

The diagnosis is usually clinical but may be aided by Wood’s light (which ranges from pale white to yellow-green, red, or black, depending on the precise species), KOH examination demonstrating concretions, and cotton-like structures on dermoscopy. (1, 2, 5) If need be, cultures can be performed. (2)

TB should be easily differentiated from black piedra (caused by Piedraia hortae), white piedra (caused by organisms in the Trichosporon genus), (6) pediculosis, hair shaft abnormalities (trichorrhexis nodosa, monilethrix), or hair coating from applied products. (4) Treating TMA is straightforward and successfully managed by shaving (if desired), antiperspirants, and topical antibiotics (clindamycin, erythromycin, or fusidic acid). (4)

One of my favorite articles from my long-ago residency was written by the Doctors Shelley, seeking out TA and pitted keratolysis (PK) in two patients who presented with erythrasma. Their astute observations formed the concept of the “corynebacterial triad” (3), which Rho and Kim subsequently confirmed. The authors evaluated 108 Korean soldiers with PK; 45 patients (41.7%) had erythrasma and PK; 22 patients (20.4%) had TMA and PK; the coexistence of erythrasma, TMA, and PK was noted in 14 patients (13.0%). (7)

Time will tell if the term trichobacteriosis supplants trichomycosis axillaris. There is room for both because it teaches us how science moves forward, especially with keenly observant clinicians such as the Shelleys. On a personal note, the last time I saw the Shelleys was serendipitously at a souvenir shop in Ketchikan, Alaska, in 2002. Their warmth, humor, and zest for life and knowledge have always been an inspiration. It is never too late to say thank you.

Point to Remember: Trichobacteriosis is the more accurate name for the corynebacterial infection with the misnomer of trichomycosis axillaris.

Our expert’s viewpoint

Mary Maiberger, MD, FAAD
Assistant Professor of Dermatology, George Washington University School of Medicine
Chief of Dermatology, Washington, D.C. VA Medical Center

At the end of an afternoon dermatology clinic some years ago, my astute resident burst into the attending office, announcing, “I think I have a patient with trichomycosis axillaris!” The patient had complained of body odor not responding to the typical over the counter remedies. As we both entered the room, I sought out the classic findings of white concretions encircling the hair shaft in our patient’s axillae to confirm the diagnosis. A Wood’s light revealed pale aggregates of bacteria coating the hair. Dermoscopy demonstrated waxy sheaths encasing the hair, as though it had been dipped in wax. This finding is often described as the “feather and skewer signs” or “rosary of crystalline stones”. (2) What a classic and satisfying diagnosis to make in clinic! Unlike many conditions we encounter in dermatology, trichomycosis axillaris is immediately recognizable and readily treatable. We can reassure the patient and recommend shaving of the area and application of topical antibiotics.

Dr. Heymann eloquently describes the misnomer in the name “trichomycosis,” a condition that should rather be termed, “trichobacteriosis” due to bacteria causing the condition rather than fungi contributing to it. While this alternate name does more accurately describe the pathophysiology, new terms or eponyms for conditions are slow to catch on, and I suspect many dermatologists will continue to refer to the condition by its original name. Regardless of the name we call it, when I encounter trichomycosis in clinic, I am reminded of the gratification that the teaching and practice of dermatology brings.

---

References

1. Murphy E, Maiberger M. Trichomycosis Axillaris. N Engl J Med. 2022 Dec 1;387(22):e59. doi: 10.1056/NEJMicm2206453. Epub 2022 Nov 26. PMID: 36440843.

2. Montes de Oca-Loyola ML, Lumbán Ramírez P, Gómez-Daza F, Bonifaz A. An Overview of Trichobacteriosis (Trichomycosis): An Underdiagnosed Disease. Cureus. 2023 Sep 25;15(9):e45964. doi: 10.7759/cureus.45964. PMID: 37900398; PMCID: PMC10600505.

3. Shelley WB, Shelley ED. Coexistent erythrasma, trichomycosis axillaris, and pitted keratolysis: an overlooked corynebacterial triad? J Am Acad Dermatol. 1982 Dec;7(6):752-7. doi: 10.1016/s0190-9622(82)80158-8. PMID: 7174913.

4. Bian K, Ma Y, Hu W. Trichomycosis axillaris. CMAJ. 2024 Oct 14;196(34):E1170. doi: 10.1503/cmaj.240723. PMID: 39406417; PMCID: PMC11482653.

5. Gupta V, Sharma VK. Four views of trichomycosis axillaris: Clinical, Wood's lamp, dermoscopy and microscopy. Indian J Dermatol Venereol Leprol. 2018 Nov-Dec;84(6):748-749. doi: 10.4103/ijdvl.IJDVL_567_17. PMID: 29516899.

6. Bieber AK, Pomeranz MK, Kim RH. White Piedra. JAMA Dermatol. 2021 Mar 1;157(3):339. doi: 10.1001/jamadermatol.2020.4266. PMID: 33471028.

7. Rho NK, Kim BJ. A corynebacterial triad: Prevalence of erythrasma and trichomycosis axillaris in soldiers with pitted keratolysis. J Am Acad Dermatol. 2008 Feb;58(2 Suppl):S57-8. doi: 10.1016/j.jaad.2006.05.054. PMID: 18191714.

---