Do Socks Harbor Fungal Pathogens?

I am writing a chapter for a sports medicine text and have been reviewing studies about new technologies relevant to athletic hosiery. Among the more recent trends has been the incorporation of antimicrobial materials into sock fibers to provide health benefits for the user. While this concept appears to be more consumer hype than true benefit, further reading has convinced me that hosiery, by itself, can play a role in spreading fungal infection in the feet as well as playing a role in failure of treatment.

Podiatric physicians are well aware of the challenges of treating and preventing recurrence of fungal infections in the feet. Thirty percent of patients with tinea pedis treated with topical agents will fail to respond or relapse.¹ Research blamed this high failure rate on non-adherence.² However, there may be another significant factor that we have commonly overlooked.

A new study validates previous speculation that socks could harbor fungal pathogens and contribute to reinfection during treatment. Amichai and coworkers cultured sections of socks worn by 81 patients, who were treated for tinea pedis and onychomycosis.³ All of the patients’ feet had confirmation of infection, showing positive culture with Trichophyton rubrum. All of the cultured samples taken from the socks contained microorganisms. Over 50 percent of the sock samples from the patients contained Trichophyton rubrum and Trichophyton mentagrophytes.

What is most interesting is when the contaminated socks worn by patients with tinea pedis and onychomycosis were laundered in a domestic washing machine at 40ºC.³ Thirty-six percent of the socks revealed positive fungal cultures at the end of the cleaning and drying cycle. When the contaminated socks were washed at 60ºC, only 6 percent tested positive for fungus, all with Aspergillus species. Laundering at 60ºC water temperature essentially eliminated T. rubrum.

To put this into perspective, 40ºC is basically body temperature (104 degrees) while 60ºC is 140ºF, which is equivalent to a hot cycle in a domestic washing machine. There is a trend toward energy conservation and protection of textiles by laundering clothing in warm or cold water. When looking at socks worn by patients with fungal infections of the feet, we can see the hazards of this practice.

Hammer and colleagues studied the propagation of fungal dermatophytes before and during domestic laundering of hosiery.⁴ In the first phase of this study, researchers showed that socks containing Trichophyton rubrum and Candida albicans could contaminate other laundry stored in the same clothes basket. Ten percent of clean or sterile laundry specimens stored in contact with contaminated sock specimens for one hour became contaminated, which the researchers verified via positive fungal culture results. When the contaminated socks were laundered at 30ºC with detergent bleaching agents, over 50 percent of the socks demonstrated positive culture for Trichophyton rubrum after washing. Increasing the temperature to 60ºC effectively eradicated all of the T. rubrum. Both washing temperatures eliminated C. albicans.

Hammer and colleagues also found that while washing at 30ºC, 16 percent of the initial spore load of T. rubrum from the contaminated socks remained in the rinse water of the washing machine.⁴ They speculated that this rinse water could effectively contaminate all of the textiles in the washing machine that were mixed with the socks worn by fungus infected patients.

This becomes a bit scary when considering that most households wash socks in the same machine with underwear and even bed linens. Could this be why a certain percentage of patients with tinea pedis also suffer from tinea cruris (i.e. jock itch)?  

Even if we wash our socks separately, they may not always end up free of fungus even if we wash them according to our standard tradition. To drive home this point, researchers asked patients who were being treated for onychomycosis and tinea pedis at a dermatology clinic to bring in a pair of “clean,” freshly laundered socks for examination.⁵ Cultures confirmed that fungal contamination with T. rubrum was present in 10 percent of the laundered socks, indicating that exposure to the fungus would continue in those patients who washed their socks with traditional protocol.

These findings may justify the wearing of hosiery containing antimicrobial fibers to counteract the potential for re-infection during fungal treatment. Indeed, socks containing fibers impregnated with copper or silver have gained popularity.⁶ At least one study has shown positive effects treating tinea pedis in patients using copper-impregnated socks.⁷ However, after reviewing the current medical literature, it is clear that further research is necessary in this area to determine the true benefit of antimicrobial sock therapy.

In the meantime, I can make the following recommendations to clinicians treating patients for tinea pedis and onychomycosis in regard to hosiery.

1. Dermatophytes can definitely colonize and survive for long periods of time in the socks worn by patients with tinea pedis and onychomycosis.

2. These socks can contaminate other laundry stored in the same container or laundry basket.

3. These socks can potentially contaminate sterile laundry in the same washing machine if the temperature of the water is below 60ºC.

4. Contaminated socks can be the source of reinfection when worn by patients being treated for fungal infections of the skin of the feet.

This blog is only focusing on the role of hosiery in the propagation of fungal infections of the feet. I have not even touched on the subject of contamination of shoes by dermatophytes, which was previously studied along with the role of ultraviolet light sterilization by Zatcoff and colleagues.⁷ Either way, clinicians and patients need education about these often overlooked reasons for failure of treatment of onychomycosis and tinea pedis. 

References

1. Bell-Syer SEM, Hart R, Crawford F, et al. A systematic review of oral treatments for fungal infections of the skin of the feet. J Dermatol Treat. 2001; 12(2):69–74.

2. Balkrishnan R, Arbor A, Fleischer A, Hardas B, Gatwood J, Plaum S. Defining pharmacologic treatment failure in tinea infections using medical claims data. J Am Acad Dermatol. 2012;66(Suppl):AB87.

3. Amichai B, Grunwald MH, Davidovici B, Farh R, Shemer A. The effect of domestic laundry processes on fungal contamination of socks. Int J Dermatol. 2013; 52(11):1392–1394.

4. Hammer TR, Mucha H, Hoefer D. Infection risk by dermatophytes during storage and after domestic laundry and their temperature- dependent inactivation. Mycopathologia. 2011; 171(1):43–49.

5. Bonifaz A, Vázquez-González D, Hernández MA, et al. Dermatophyte isolation in the socks of patients with tinea pedis and onychomycosis. J Dermatol. 2013; 40(6):504-5.

6. Quirós J, Borges JP, Boltes K, et al. Antimicrobial electrospun silver-, copper- and zinc-doped polyvinylpyrrolidone nanofibers. J Hazard Mater. 2015;299:298-305.

7. Zatcoff RC, Smith MS, Borkow G. Treatment of tinea pedis with socks containing copper impregnated fibers. Foot. 2008;18(3):136–41.

8. Ghannoum M, Isham N, Long L. Optimization of an infected shoe model for the evaluation of an ultraviolet she sanitizer device. J Am Podiatr Med Assoc. 2012; 102(4):309-13.