- 1 What is Fungus?
- 2 Fungal Nail Infection
- 3 Statistics on Onychomycosis
- 4 Risk Factors for Fungal Nail Infection
- 5 What Do These Fungal Nail Infections Usually Look Like?
- 6 Types of Fungal Infections of the Nail
- 7 Diagnosing Fungal Toenail Infection
- 8 Managing Onychomychosis
- 9 Prevention of Fungal Toenail Infections
What is Fungus?
Fungi are one of the most widely disseminated organisms. Having around 80,000 species, they are of great medical and environmental importance. Among the examples of fungi include molds, mildew, mushrooms, rusts, smuts, toadstools and yeasts. 
Although most fungi are not a threat to human health, a number can be quite dangerous, and even lethal, leading to opportunistic, hospital-associated and community-acquired infections . Discussing the simple and benign fungal cases is just as important as learning about the fatal , more dangerous ones.
This is an article tackling one of those simpler, more common, yet also important fungal infection — the fungal toenail infection.
Fungal Nail Infection
Medically termed as Onychomycosis, these fungal infections frequently affect the big and small toes. A person can even have several nails infected, most of them usually on the same foot or hand. 
It is usually caused by Trichophyton rubrum, a dermatophyte, molds Scopulariopsis brevicaulis and the yeast Candida parapsilosis. These fungi commonly thrive on nails after an injury, when their barriers are weak. [3, 4]
A photo showing toenails infection with fungi.
Statistics on Onychomycosis
Recent surveys in South East Asia show that 10% of the adult population suffer from fungal infection of the nails. Most of whom have been infected for more than half a decade and with relatives infected with the same illness. 
In the United Kingdom, onychomycosis is a fairly common problem. It affects three people out of every 100 population. In fact, half of the problems affecting the nails in this region can be rooted from fungi. 
Risk Factors for Fungal Nail Infection
Onychomycosis is usually an antecedent of a previous fungal foot infection. These are those people who frequent public pools and shower rooms, and those who excessively perspire. Also included in the high risk group are the immunocompromised, with a minor nail or skin injury and disease, with psoariasis or diabetes, often wearing closed shoes, with wet or moist feet most of the time, usually in a humid environment, and those whose feet were cleaned unhygienically (poor antiseptic technique during pedicure and manicure sessions). [6, 7]
What Do These Fungal Nail Infections Usually Look Like?
In general, fungal infections start at the nail edges, slowly easing its way en route to the nail base. The infected nail would then be thickened and stained with a greenish, yellowish, whitish, or blackish hue. It will eventually lack luster, with its tip loosened and even lifted (termed as onycholysis). The nail can even be deformed, brittled, with crumbled edges and fragments trapped under it. [3, 6, 7, 8]
An image of blackened toenails, a characteristic typical of fungal infection.
Types of Fungal Infections of the Nail
Onychomycosis can be classified into 5 types: white superficial, distal subungual, proximal subungual, total dystrophic and candidal. [9, 10, 11]
White Superficial Onychomycosis
This type of fungal nail infection usually presents as well defined white, opaque superficial markings with crumbled edges on the nail plate. Occurring mostly in the toenails, this usually occurs when fungi affect the nail plate superficially. Because less tissues are involved, inflammation is miniscule.
An image of a toenail with white superficial onychomycosis.
Distal Subungual Onychomycosis
The most common type of onychomycosis, distal subungual is usually brought about by Trichophyton rubrum. It affects both the nail plate and the nail bed. It is characterized by a thickened subungual area, onycholysis, and a yellowish brown nail plate.
A photo representing an example of distal subungual onychomycosis.
Proximal Subungual Onychomycosis
Also called proximal white subungual onychomycosis, this type is uncommon. In this type, the fungi invades the cuticle area of the proximal nail fold, affecting the nail plate and spreading to the distal areas. More common among the immunocompromised, it usually presents as onycholysis, destruction of the nail plate, and subungual hyperkeratosis.
An image depicting proximal subungual onychomycosis.
Total Dystrophic Onychomycosis
In this type, complete nail plate dystrophy ensues. There is a thickened, dystrophic nail. It is also used to describe end stage nail disease and may be the sequelae of any of the other types of onychomycosis.
An example of a toenail with total dystrophic onychomycosis.
This type usually occurs after a preceding injury, infection or damage to the nail. It is usually caused by Candida albicans, and is initially presented as paronychia, an infection of the surrounding structures of the nail. It can appear as oblique depressions called Beau’s lines, have a pseudo clubbing appearance, or seen as onycholysis.
Diagnosing Fungal Toenail Infection
After a thorough history taking and physical examination, confirmation of fungal infection is a must prior to treatment. The diagnosis can be ascertained by a smear using potassium hydroxide (KOH), culture and histology. This is done by microscopically examining the scrapings gotten from the underside of the nails. This method can determine the fungus type, and subsequently, determine the correct method of management. The samples can also be cultured, with results noted within 3 weeks. [7, 12]
Various treatment modalities may be used for the management of fungal toenail infection. These include oral medications, lacquer, topical drugs and even surgery.
Antifungal medicines taken per orem include Terbinafine, Fluconazole, Itraconazole and Griseofulvin. These are usually taken for 2 to 3 months. They are deemed as the treatment modality with the highest success rate, however, causing a few adverse reactions such as skin rashes and liver injury. [6, 7, 8]
This antifungal nail polish is usually prescribed for mild to moderate infection. It is applied on infected nails once a day every 7 days. Some studies have even recommended a combination treatment of lacquer and oral antifungals. [8, 13]
Antifungals applied topically may not completely eliminate the fungi, however they can be used as adjunct treatment in treating the infection. These medications can be applied after the thickened nail had been filed and thinned enough that the topical medication can be absorbed. 
This can be the option preferred when the fungal infection is already severe. The nail can be surgically removed and an antifungal lacquer can be used as an adjunct. 
Prevention of Fungal Toenail Infections
Aside from the treatment modalities mentioned above, prevention is also of utmost importance, more so that fungal infections are usually chronic and relapsing. Below are a number of ways on how to prevent fungal infection of the toenails: [7, 8, 14]
- Maintain proper hygiene and care of nails.
- Keep the skin dry and clean.
- Maintain clean and well sterilized equipments for pedicure use.
- Wear open toed shoes from time to time to avoid too much moisture on the feet.
- Avoid going barefoot in public areas.
- Use antifungal foot powder or spray.
- Wash hands after contact with an infected nail.
- Consult doctor if faced with such symptoms.
- Nenoff, P. Fungal Nail Infections- An Update: Part 1: Prevalence , Epidemiology, Predisposing Conditions, and Differential Diagnosis. Hautarzt. 2012 Jan; 63 (1): 30-8
- Elewski, B. Onychomycosis: Pathogenesis, Diagnosis and Management. Clinical Microbiology Review. 1998 July; 11 (3): 415-29
- Gupta, A. Types of Onychomycosis. Cutis. 2001 Aug; 68 (2): 4-7
- James, W. et al. Andrews’ Diseases of the Skin: Clinical Dermatology. Saunders Elsevier. 2006
- Rodgers, P, et al. Treating Onychomycosis. American Family Physician. 2001; 63(4): 663-72