Since dermatophytes are ubiquitous in the environment, mycotic nail disease is the most common nail pathology worldwide reaching all cultures and ethnicities. Onychomycosis is increasing, accounting for up to 90 % of toenail and at least 50 % of fingernail infections [1]. Onychomycosis occurs in 10 % of the general population, 20 % of individuals 60 years and older, and 50 % of individuals over 70 years [2]. That said, it’s not just the patient being exposed to the dermatophyte in the environment, it’s also a combination of patient health and genetic predisposition to create the perfect situation for fungus to take hold. Peripheral vascular disease, immunologic disorders, and diabetes mellitus correlate with increased prevalence in older adults. The risk of onychomycosis is 1.9–2.8 times higher in persons with diabetes mellitus, and in patients with HIV infection, prevalence rates range from 15 to 40 % [2]. Other predisposing factors include older age, sex (male > female), genetic predisposition, tinea pedis (interdigital or moccasin types), peripheral arterial disease, smoking, nail trauma, inappropriate nail hygiene, and family background of onychomycosis and hyperhidrosis [2].

Adult patients constitute the bulk of those seeking treatment, but there are increasing numbers of pediatric cases, possibly due to increasing childhood obesity and pediatric diabetes. With prevalence ranging from 0 to 2.6 % worldwide, pediatric onychomycosis is relatively rare compared to adults, but still one of the most common nail disorders in children [3]. Ultimately, it is a multifactorial disease that is not solely caused by poor hygiene or poor choices of shoe gear.

The practitioner is often faced with hearing the following “cures” for onychomycosis on a daily basis: Listerine, Vicks VapoRub, oil of oregano, apple cider vinegar, bleach, and tea tree oil, to name a few. Patients are inundated with various remedies in the foot care aisle in their local pharmacy promising a clear nail in a small amount of time.

Apple cider vinegar (ACV) is touted as a cure all tonic for many different ailments and has websites dedicated to its properties. It is generally inexpensive and easy to obtain. Patients are bombarded with faceless, picture-less “my toenails look better!” testimonials that claim the anonymous person’s nail disease was cured. What is in apple cider vinegar? Maleic acid, acetic acid, pectin, beta carotene, acetoin, methanol, alanine, ethanol, ethyl acetate, lactic acid, methanol, glycerol, and tartaric acid, in addition to mineral salts, phosphorus, potassium, chloride, sodium, and other minerals [4, 5]. It’s the maleic acid that purportedly has the properties of being both bactericidal and fungicidal. Some have theorized that acetate can inhibit lanosterol demethylase which means it would impact ergosterol production in a fungal cell; others have felt that acetic acid is permeable to the cell membrane and the presence of it is toxic to the cell [6, 7].

There have been no clinical trials showing that it creates a mycological or clinical cure for onychomycosis. The closest study to dissect ACV’s antifungal properties was in the Journal of Prosthodontics where the authors studied ACV for denture stomatitis which is usually caused by Candida albicans [4]. This study showed the MIC (minimum inhibitory concentration) of ACV versus the common antifungal for Candida: nystatin, but more importantly, it showed the microbial death curve. The microbial death curve is a more dynamic measure, as it allows “quantitative analysis of the fungicidal activity and of the time required until microbial death” [4], ultimately showing the behavior of antifungal agent in the presence of the organism. In this study, the kinetics of antifungal activity of ACV varied at all concentrations and time intervals from nystatin and control. All groups (ACV and nystatin) showed fungistatic activity when tested at MIC and MIC × 2, between 0 and 180 min. When tested at MIC × 4, ACV exhibited fungistatic activity only between 0 and 30 min; however after 30 min, it began to exhibit fungicidal activity. So, ultimately, for Candida albicans, ACV concentration and time exposed to the organism will affect whether it acts as a funstistatic agent or fungicidal agent.

When translating this to clinical practice, there are no MIC data or microbial death curves on ACV’s effect on T. rubrum or T. mentagrophytes, the most common dermatophytes seen in toenail onychomycosis. Although it seems that ACV does exhibit antifungal behavior in vitro, we can’t make that direct connection in vivo to onychomycosis or determine the concentration/time exposed needed to have a fungicidal effect. More studies are needed to determine what, if any, true effect can be had on fungal toenails. At this stage, it remains a folk remedy with widely varying results.

Another folk remedy that is both readily found on the Internet and recommended by physicians, Vicks VapoRub (Proctor and Gamble), an over-the-counter mentholated ointment, has been described as a treatment for onychomycosis. Many physicians feel there is a cost benefit of using an easily attainable product that has no side effects, but are unaware of the research on this product.

The components of Vicks VapoRub are thymol, menthol, camphor, and oil of Eucalyptus which seem to be broad-spectrum anti-infectives that have shown activity in vitro against Candida, Aspergillus, and some dermatophytes [8]. Some data has been generated about its use for toenail onychomycosis in vivo.

The first clinical trial completed using Vicks VapoRub on mycotic nails is a pilot study that was performed by a Family Medicine Group [8]. Eighteen subjects who had nail disease completed the 48-week study. There are some positive aspects of this study, but it did not follow all of the protocols that are normally done for topical antifungal studies. Unlike phase 3 clinical trials for toenail onychomycosis, this study did not exclusively enroll patients who cultured dermatophytes like T. rubrum or T. mentagrophytes and did not limit the percent of affected nail to 50 or 60 %. Instead, they allowed patients who cultured organisms like “fungal elements,” Cryptococcus, Candida, Penicillium, and Fusarium and allowed up to 100 % of the nail affected visually. Of the 18 patients, only nine subjects cultured either T. rubrum or T. mentagrophytes.