Syphilis is a systemic infection caused by the bacterium Treponema pallidum, known for its ability to affect multiple organ systems. Because the infection progresses through distinct stages, it often mimics other diseases, earning it the nickname of “the great imitator.” Some manifestations are dermatological, involving the skin and hair. Hair loss is a medically recognized concern, as this is one of the less common but notable signs of the disease’s progression.
The Syphilis-Alopecia Link
Syphilis does cause hair loss, a condition medically termed alopecia syphilitica, which occurs almost exclusively during the secondary stage of the infection. This stage develops a few weeks to several months after the initial infection, as the bacteria spreads throughout the body. Hair loss is a relatively uncommon symptom, affecting an estimated 3% to 7% of individuals experiencing secondary syphilis.
The mechanism behind this hair loss is not the direct destruction of the hair follicle by the bacteria. Instead, it appears to be an inflammatory immune response mounted by the body against the infection. This systemic inflammation disrupts the normal hair growth cycle, forcing hair prematurely into the resting or telogen phase.
Immune cells, particularly lymphocytes, accumulate around the hair bulb at the base of the hair follicle. This perifollicular inflammation interferes with the delicate process of hair production. The result is a non-scarring alopecia, meaning the hair follicle structure remains intact and capable of growing hair once the underlying cause is resolved.
Distinctive Patterns of Syphilitic Hair Loss
Syphilitic alopecia presents in two main patterns, with one being highly distinctive of the infection. The first and most characteristic presentation is known as “moth-eaten” alopecia, named for its specific appearance. This pattern involves small, irregular, and scattered patches of hair loss across the scalp, often concentrated in the back and sides of the head (parieto-occipital regions).
These patches are typically non-scarring, lack visible inflammation, and are not completely bald, giving the appearance of hair that has been nibbled away. The unique visual quality of the moth-eaten pattern is considered a pathognomonic sign, meaning it is highly suggestive of secondary syphilis. This specific pattern can also affect other hair-bearing areas, including the eyebrows, beard, and eyelashes.
The second form is diffuse alopecia, which presents as a more generalized thinning of the hair across the entire scalp. This presentation is less common than the moth-eaten pattern and can easily be mistaken for other common causes of widespread hair shedding, such as telogen effluvium. Individuals may sometimes present with a mixed pattern, showing both patchy moth-eaten areas and overall diffuse thinning. The non-scarring nature of the hair loss is consistent across both patterns, which is important for determining the prognosis for hair regrowth.
Confirming the Diagnosis
Diagnosing hair loss as a symptom of syphilis requires a high degree of clinical suspicion, as the appearance can resemble other dermatological conditions. Because the hair loss alone is non-specific, a doctor must rely on blood tests to confirm the presence of the Treponema pallidum infection. The standard protocol involves a two-step serological testing process.
The first step uses non-treponemal tests, such as the Rapid Plasma Reagin (RPR) or the Venereal Disease Research Laboratory (VDRL) test, which detect non-specific antibodies. If this screening test is positive, a second, more specific treponemal test is performed to confirm the diagnosis. These confirmatory tests, like the Fluorescent Treponemal Antibody Absorption (FTA-ABS) or Treponema pallidum Particle Agglutination (TPPA) assay, detect antibodies specifically directed against the syphilis bacterium.
In rare instances where the diagnosis remains unclear, a skin biopsy of the affected scalp area may be considered. A biopsy can reveal inflammatory cells around the hair follicles, and specialized staining techniques may occasionally visualize the spirochete bacteria. However, this procedure is not typically required, as a positive serology combined with the distinctive clinical appearance is usually sufficient to confirm that syphilis is the cause of the hair loss.
Treatment and Hair Regrowth
Since alopecia syphilitica is a symptom of the bacterial infection, treatment focuses entirely on eradicating the Treponema pallidum. The preferred and most effective treatment for secondary syphilis is a single intramuscular injection of benzathine penicillin G. This antibiotic is highly effective against the bacteria and addresses all systemic manifestations, including the hair loss.
For individuals with a documented penicillin allergy, alternative antibiotics, such as doxycycline or tetracycline, may be prescribed over a period of two to four weeks. Once the infection is successfully treated, the inflammatory response disrupting the hair cycle subsides.
The prognosis for hair regrowth is very favorable because the hair loss is non-scarring, meaning the hair follicles were never permanently destroyed. After treatment, hair regrowth is typically complete, though it is not immediate. Hair usually begins to regrow within a few weeks to three months following the administration of the antibiotic.