Green Nail Syndrome (GNS, Pseudomonas nail infection, chloronychia, green striped nails, chromonychia)

Are You Confident of the Diagnosis?

What you should be alert for in the history

Green nail syndrome is caused by infection with Pseudomonas aeruginosa. Patients likely have a history of prolonged exposure to water or detergents (soaps), or an ungual trauma.

Characteristic findings on physical examination

On physical examination, there is characteristic greenish or greenish-black discoloration of the nailfold with proximal chronic paronychia and distolateral onycholysis (Figure 1, Figure 2, Figure 3, Figure 4). A small portion of the nail may be involved or the entire nail itself. Most patients will only have involvement of one nail. On occasion, the nail adjacent to the primarily infected nail will have some secondary evidence of infection. Green striping of the nail has also been reported.

Figure 1.

Green nail syndrome.

Figure 2.

Green nail syndrome.

Figure 3.

Green nail syndrome.

Figure 4.

Coinfection with Trichophytan rubrum and Pseudomonas, a common occurrence.

Expected results of diagnostic studies

Diagnostic studies are typically unnecessary. Gram stain and culture of any exudates and/or ungual fragments may confirm the diagnosis; however, culture can be negative, as the green discoloration may be found a distance away from the infected site.

A pigment solubility test might also be performed, by submerging a sample of the affected nail in 1mL of distilled water. The liquid will turn a bluish-green color within 24 hours if there is a present infection with P. aeruginosa. Wood’s light examination will occasionally show a yellow-green fluorescence, which is characteristic of Pseudomonas.

Diagnosis confirmation

The differential diagnosis includes the following conditions:

– Subungual hematoma is a collection of blood between the nailbed and fingernail following a direct injury. On physical exam, there is reddish to reddish-black pigment, depending on the age of the blood, and the nail is tender to the touch. On dermoscopy, small reddish to reddish-black globules are appreciated. The hematoma will grow out as the nail plate grows.

– Longitudinal melanonychia presents as horizontal or longitudinal bands of nail darkening. On dermoscopic exam, grayish bands of pigment can be appreciated. There are many causes of longitudinal melanonychia, including drugs, radiation, human immunodeficiency virus (HIV) infection, inflammatory nail disorders, Laugier-Hunziker syndrome, vitamin B12 or folate deficiency, and systemic lupus erythematosus.

– Onychomycosis is a fungal infection of the nail apparatus characterized by a yellowish discoloration of the nail, along with subungual hyperkeratosis and eventual onycholysis. Diagnosis is confirmed by a positive nail culture for fungi. This can be commonly seen in addition to green nail syndrome.

– Subungual melanoma is the most serious diagnosis in the differential. It is more likely to be dark black (and less green) in coloration. White areas (indicative of regression) and extension of pigment around the cuticle (Hutchinson’s sign) should be concerning features. Invasion of melanoma may cause papules, plaques, ulcerations, and nail deformities. Dermoscopic features include parallel longitudinal brown-to-black lines with irregular color, thickness, or spacing. If there is any concern for melanoma in the differential diagnosis, a biopsy should be performed.

– Other Infections: Aspergillus, Proteus, and Candida species have been implicated. These species may be contaminants, and more research is required to consider them pathogenic in causing green nail syndrome.

Who is at Risk for Developing this Disease?

Any individual that has prolonged nail exposure to water sources is more prone to developing green nail syndrome. Predisposing factors can include onychomycosis, and the two infections are often seen together. Nail trauma (biting, chewing, tearing) and nail deformities or onycholysis may increase the risk for developing green nail syndrome. One of the larger series showed a female predominance of 35 to 5.

Those with fingernail infection are often working as bartenders, dishwashers, waiters, or other occupations with significant water exposure.

Those with toenail infections are often individuals that work in hot humid environments that require footwear. The moisture builds up from sweat and maceration, and the bacteria are able to thrive.

Those with artificial nails may be at an increased risk for developing this bacterial infection, although no good studies have proven the link.

Dry skin and dry nails do not offer an environment conducive to Pseudomonas bacterial growth. The bacterium requires moist conditions to thrive. Macerated toe web spaces are an excellent breeding ground for the bacteria, and may serve as the initial source for the nail to become infected. Occasionally, the greenish discoloration or tint can be seen in the toe web spaces.

What is the Cause of the Disease?

The ubiquitous gram-negative facultative anaerobic bacteria Pseudomonas aeruginosa is the causative organism. It causes opportunistic infections. The bacterium is found routinely in soil and water sources. Pseudomonas grows and multiplies rapidly in warm water.

Pseudomonas aeruginosa is capable of producing a variety of pigments, the most well known being pyocyanin, which is a blue-green pigment. The bacterium is typically grown on blood agar, MacConkey agar, or Pseudomonas isolation agar in the lab. It is lactose negative on MacConkey agar.

The bacteria move by action of a single motile polar flagellum, and are approximately 3μm in length. The bacterial colonies have a distinct odor of Concord grapes when grown on blood agar or MacConkey agar culture plates.

The stratum corneum serves as a physical primary defense to infection. Any hyperhydration (occlusion, sweating, maceration) or destruction (microtrauma, dermatitis) of the epidermis interrupts the physical barrier and may lead to colonization and proliferation of P. aeruginosa.

Collagenase, elastase, phospholipase, heat-stable thermolysin, vascular permeability factor, and fibrolysin are all produced by P. aeruginosa and facilitate spread of infection after invasion of the epidermis. The bacteria are able to digest keratin and this may explain the organism’s ability to invade the nail plate. This bacterium is capable of producing various pigments, including pyocyanin, pyoveridine, and pyorubin.

Aspergillus and Candida species have been implicated as a cause of green nail syndrome. Whether these are truly pathogenic organisms remains to be proven. They are more likely to be coinfections along with Pseudomonas aeruginosa.


The green discoloration of the nail is due to the pigment pyocyanin, which is produced by the bacterium Pseudomonas aeruginosa. This pigment can be green to dark green (appearing nearly black).

Systemic Implications and Complications

The individual with green nail syndrome will typically have no systemic complications. Rare reports have been given of self-inoculation of the bacteria into the skin after patients accidently scratched themselves with an infected nail. This may lead to a self-induced skin or soft tissue infection with Pseudomonas (wound infection or possibly cellulitis).

There is a case report of a patient with green nail syndrome that recently underwent removal of a basal cell carcinoma. During his care of the surgical wound, he transferred the bacteria to the wound, thus causing a localized Pseudomonas wound infection.

Individuals with green nail syndrome that work in hospitals have been implicated in transferring the bacteria to patients. This is a potential source for nosocomial infections.

Treatment Options

Treatment options are summarized in Table I.

Table I.
Medical Modality Surgical modality Physical modality
Acetic acid soaks Nail removal surgery may be required for onychodystrophy. Trim nail back
Topical aminoglycosides (neomycin, gentamicin, polymyxin-B)   Keep nails dry
Topical fluoroquinolones   Wear cotton-lined rubber gloves during wet work
2% sodium hypochlorite, twice daily    
0.1% octenidine dihydrochloride solution (available only in Europe at this time)    

Optimal Therapeutic Approach for this Disease

Culture of the nail plate is important to help determine if there is an underlying dermatophyte infection. If an infection is found, this should be treated accordingly.

Culture of the nail for bacterial culture is typically not warranted, and the diagnosis is made on clinical grounds. Dark- to bright-green discoloration of the nail plate is indicative of the diagnosis.

A Gram stain can be used to look for gram-negative rods. If a nail culture is performed, inform the lab that you would like a Pseudomonas culture. This courtesy allows the lab to properly set up culture plates to maximize the results. When nail cultures are sent to the lab without any information, the standard procedure is to do a fungal culture, looking only for onychomycosis.

Initial therapy is white vinegar (acetic acid) soaks. Use 1 part white vinegar and 4-10 parts water (depending on concentration of white vinegar). The goal is a 0.25%-1.0% acetic acid concentration. Soak for 10 minutes, twice daily, then thoroughly dry. Treatment can require a few weeks to months. (Any vinegar will work; the advantage of white vinegar is that it is inexpensive, does not stain clothing, and the odor dissipates rather quickly.)

Liquid vehicles, such as solutions or lotions, will work better than creams or ointments. These vehicles dry quicker and can work their way underneath onycholytic nail plates. Recommendations include:

  • Gentamicin 0.3% solution, 1-2 drops to the affected nail, twice daily.

  • Neomycin + polymyxin B + gramicidin (Neosporin Solution®), 1-2 drops to the affected nail, twice daily.

  • Oflaxacin 0.3% solution, 1-2 drops to the affected nail, twice daily (Expensive).

Patient Management

Most patients will respond quickly and fully. The key to good results is preventing future infections by minimizing wet work, keeping nails dry, and avoiding trauma as much as possible.

Patients should call after one month with a follow-up report. If the nail is back to normal, patients can follow preventative measures, and no further follow-up is needed. If the nail is still green after one month’s time, patients can continue for another month and then be seen at the end of that second month of therapy. At the follow-up appointment, it may be necessary to change therapies to a gentamicin solution.

Oral treatment with a fluoroquinolone is usually not required, and is not recommended as a therapy for children.

In adults, ciprofloxacin, 500mg orally, twice a day for 7 days, has been reported to be successful. These individuals must also avoid wet work, dry their nails to the best of their ability, and consider using the topical therapies in conjunction with the oral ciprofloxacin.

Nail avulsion has also been used successfully. Nail avulsion is a therapy of last resort, unless a form of onychodystrophy is the cause of the green nail syndrome. In these cases, the patient can try topical therapies, but should be advised that nail avulsion may be required.

If there is any suspicion of subungual melanoma, a prompt biopsy should be done.

Unusual Clinical Scenarios to Consider in Patient Management

The infection may produce a chronic paronychia if left untreated. It has been found that onycholysis preceded the development of paronychia in most cases.

Hot humid climates may require longer treatment than cold dry climates.

It is highly unusual to have more than two nails involved.

What is the Evidence?

Silvestre, JF, Betlloch, MI. “Cutaneous manifestations due to Pseudomonas infection”. Int J Dermatol. vol. 38. 1999. pp. 419-31. (A nice review of Pseudomonas infections, including microbiology, epidemiology, and pathogenesis)

Baron, EJ. “Rapid identification of bacteria and yeast: summary of a national committee for clinical laboratory standards proposed guidelines”. Clin Infect Dis. vol. 33. 2001. pp. 220-5. (Thorough review of bacterial identification by various laboratory methods. Describes the characteristics of Pseudomonas bacteria when grown on various culture media. This reference is a guide for microbiology; it does not discuss clinical diseases.)

Agger, WA, Mardan, A. “Pseudomonas aeruginosa infections of intact skin”. Clinical Infectious Diseases. vol. 20. 1995. pp. 302-8. (Nice review of various pseudomonal skin infections. They use case vignettes to explore and highlight the various skin infections caused by Pseudomonas aeruginosa. Green nail syndrome is briefly discussed, along with a few treatment options.)

Tosti, A, Piraccini, BM, Bolognia, JL, Jorizzo, JL, Rapini, RP. “Nail Disorders”. Dermatology. 2008. pp. 1023-4. (Brief overview of green nail syndrome. Treatment options are discussed.)

Shellow, WVR, Koplan, BS. “Green striped nails: chromonychia due to Pseudomonas aeruginosa”. Arch Dermatol. vol. 97. 1968. pp. 149-53. (First case report of green striping of the nail caused by Pseudomonas. The striping was represented by horizontal green ridges of the nail plate, felt to be caused by the associated pseudomonal chronic paronychia in this patient.)

Chernosky, ME, Dukes, CD. “Green nails”. Arch Dermatol. vol. 88. 1963. pp. 548-53. (One of the largest case series ever reported: forty patients (thirty-five females, five males). Thirty-two patients worked in an occupation with excessive exposure to water. Seventeen patients reported some form of nail trauma preceded the infection.)

Rigopoulos, D, Rallis, E, Gregoriou, S. “Treatment of Pseudomonas nail infections with 0.1% octeninide dihydrochloride solution”. Dermatology. vol. 218. 2009. pp. 67-8. (A fifteen-patient series, with eleven females and four males. The authors determined this to be a safe effective therapy for green nail syndrome. This topical antibiotic is only available in the European Union. Twelve of fifteen patients were cured after 6 weeks of therapy.)

Vergilis, I, Goldberg, LH, Landau, J. “Transmission of Pseudomonas aeruginosa from nail to wound infection”. Dermatol Surg. vol. 37. 2011. pp. 105-6. (Case report of a patient that had skin cancer surgery. He developed a postoperative wound infection with Pseudomonas. On closer inspection, he had green nail syndrome and it was felt that he autoinoculated the surgical site.)