Analysis of the role of nail polish in the transmission of onychomycosis (2024)

Dear Editor,

Onychomycosis is one of the most important nail fungal infections in the world.Dermatophytes are the most common fungal agent, with Trichophytonrubrum being the most prevalent. The prevalence of T.rubrum is due to its high virulence and keratinophilic nature. This agentis also the species most adaptable to humans, causing chronic diseases.¹ Transmission of onychomycosis occursthrough direct or indirect contact with contaminated objects. The role of nail tools intransmitting dermatophytes is known, though there are few studies discussing thepossibility of fungal transmission through nail polishes. Hence, this study aimed toanalyze the viability of Trichophyton rubrum in nail polishes, basecoat and top coat, which were experimentally contaminated, after different periods oftime.

This study used a clinical strain of Trichophyton rubrum from the fungalcollection of the Mycology Laboratory of the School of Medicine, Universidade Federal doRio Grande (FURG). T. rubrum was incubated for 7 days at 25º C inpotato agar (PDA) to obtain a young culture. After this period, the fungal inoculum wasstandardized according to the protocol M38-A2 (CLSI).² The inoculum concentration was adjusted to 2-6x10⁴ CFU/ml, using the Neubauer chamber.

The nail polishes used in this study comprised a red, a white, a base coat, and a topcoat from three main commercial brands (“X”, “Y” and “Z”). In a biosafety cabinet, usinga sterile pipette, 3.0-3.5 ml of nail polishes was removed from each bottle, leaving atotal volume of 4.5ml. Next, 500µl of the standardized inoculum was added to eachbottle (1:10 dilution), resulting in a contamination with 2-6x10³ UFC of T. rubrum/ml ofnail polishes.

To determine the fungal viability after homogenization, 100µl from each bottle ofcontaminated nail polish were incubated in duplicate on Petri plates. The samples werespread over Sabouraud agar using their respective nail polish brushes and a Drigalskispatula. The inoculations were performed at time 0 (immediately following contaminationand homogenization), at 72 hours, and 60 days post-contamination; the bottles remainedclosed and stored at room temperature until the end of the experiment. The plates wereincubated at 25º C, with daily readings and evaluation of growth until 15 days afterincubation to assess the retrocultures of the microorganism.

Fungal growth was not observed on the plates inoculated with either the red or whitecontaminated nail polishes, nor with the contaminated base coat, at any testing time (0,72 hours and 60 days). In contrast, positive retrocultures of T. rubrum werefound in the top coat of all brands (“X”, “Y” and “Z”) at time 0, and oftwo brands at 72 hours and 60 days (Figure 1).

This study has shown the capacity for T. rubrum development in top coat,even 60 days after inoculation. These results are consistent with the study ofGonçalves et al.,³ in which tested nail polishes showed fungal growth after 30 days.These findings emphasize the possibility for top coat to act as a fomite, confirming itssignificance in the dispersal and indirect transmission of onychomycosis.

Given that the clinical features of onychomycosis include frequent and often abundantpeeling of the nails, abrasion of the polish brush on an affected nail would probably besufficient to carry a fragment of infected keratin to the entire bottle. This wouldmaintain fungal viability, as keratin is the main substrate on which dermatophytesdevelop. In our study, T. rubrum was able to grow in top coat even inthe absence of keratin.

In contrast, the red and white nail polishes and the base coat inhibited T.rubrum growth at all analyzed times. The difference in fungal growthbetween the tested nail polishes could be due to differences in their chemical features.Most of the top coats marketed in Brazil contain mineral oil and soy oil; red/white nailpolishes and base coats, however, do not contain these substances, but do contain highlytoxic chemicals such as toluene, xylene, formaldehyde, chromium and nickel. Furthermore,the preservatives and biocides commonly present in aqueous cosmetics, such as sodiumbenzoate, potassium sorbate, benzoic acid and phenols, decrease microorganismcontamination. These substances are not added to oil-based cosmetics.⁴

Various in vivo conditions predispose onychomycosis by dermatophytes,including aspects inherent to the host (skin health; genetic characteristics; individualhabits and customs).⁵ However, theviability of dermatophytes in top coat, as described in this study, suggests that thepropagation and dispersal of this pathogen in the population can be reduced through animportant prevention measure: avoidance of sharing personal cosmetic items.