Toenail fungus often begins as an infection in the skin called tinea pedis (also known as athlete’s foot). The fungus often starts under the nail fold at the end of the nail. Over time, it grows underneath the nail and causes changes to its appearance, such as a yellow or brownish discoloration. It can also cause thickening and deformity of the toenail. 
What triggers candida in the first place? This overgrowth of yeast can develop from a number of factors, including antibiotic use, poor digestion, low immune system function, a high sugar and grain diet, stress or hormonal changes. All these create an acidic environment that encourages yeast growth and the presence of candida. Many people opt for over-the-counter anti-fungal creams or even medications, but they only treat the symptoms, not the environment that allows candida to flourish.
Walking barefoot in wet, dark areas frequented by many other individuals like indoor swimming pool decks, communal showers, and locker rooms result in frequent exposure to pathogenic fungi (dermatophytes) that cause athlete’s foot. Wearing occlusive footwear is thought to play a significant role in the increased frequency of tinea pedis. Exposure to moisture either from excessive sweating or from an external source is a risk factor. Wearing the same shoes and socks for an extended period may damage the skin. Patients with diabetes are predisposed to develop tinea pedis. Some believe that eczema (atopic dermatitis) can predispose one to tinea pedis. It appears that many more men have tinea pedis than women. Pedicure performed in contaminated environments can spread disease.
Dermatophytes — fungus that grows on the skin, hair and nails but don’t penetrate tissues of the body. Athlete’s foot or Trichophyton rubrum is the most common dermatophyte and can actually infect the toenails. Infection can also begin by touching objects that have dermatophytes on them, such as nail clippers, nail files, socks, shoes, shower floors, etc. Dermatophytes are the cause of most fungal toenail infections.
Multiple fungi species can infect the nail. Fungus grows well in warm, moist environments such as showers. Fungus infection is one of the few foot problems that affect more men than women, perhaps because more men walk barefoot in locker rooms. Age is a factor, too. Half the sufferers are people older than 70. Other risk factors include having certain medical conditions such as diabetes, vascular insufficiency and malnutrition.
Fungal athlete's foot may cause a rash on one or both feet and even involve the hand. A "two feet and one hand" pattern is a very common presentation of athlete's foot, especially in men. Hand fungal infections are called tinea manuum. Fungal athlete's foot may also be seen along with ringworm of the groin (especially in men) or hand(s). It is helpful to examine the feet whenever there is a fungal groin rash called tinea cruris, or jock itch. It is important to treat all areas of fungal infection at one time to avoid reinfection. Simply treating the soles and ignoring the concurrent fungal infection of toenails may result in recurrences of athlete's foot.

Infected nails are usually thicker than normal and could be warped or oddly shaped. They can break easily. Nails with fungus might look yellow. Sometimes a white dot shows up on the nail and then gets bigger. When fungus builds up under your nail, it can loosen and even separate the nail from the bed. The fungus can also spread to the skin around your nail.

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