Fungus Defined

• Fungus is a microscopic organism that strives in warm and moist environments and requires no sunlight to survive. Not all fungi cause infection or illness; some are beneficial and are used for various medical and culinary purposes (for instance, mushrooms are a type of fungus). Most nail fungal infections are caused by a fungus belonging to the dermatophytes group, while others may be caused by molds or yeasts.
  
  

Conditions

• Because fungi live in warm and moist environments, they tend to thrive in swimming pools and showers. Nail fungus typically develops in sweaty shoes or socks and on shower floors, infecting a lot of athletes. Athlete's foot, also a fungal infection, is not the same as nail fungus, but both can coexist and be caused by the same type of fungus.
  
  

Infection

• Fungi can penetrate the skin through tiny invisible cuts or through the separation of the nail and the nail bed. The fungus, however, will only cause a problem if the nails are continually exposed to moisture and warmth, which are the perfect conditions for the fungi to spread and grow.
  
  

Susceptibility

• Toenails are more likely to get infected with nail fungus than fingernails because toenails are more often confined inside the shoes where it is warm, dark and moist. Also, the diminished blood circulation to the toes relative to the fingers makes it harder for the immune system to detect a foreign invader and eliminate an infection.
  
  

Growth and Development

• A fungal infection typically starts with a yellow or white spot under the tip of the nail or nails. As the fungus multiplies and spreads, the infected nail will thicken and become dull with no shine or luster. Later on it will become brittle, ragged or crumbly and develop a dark color that is caused by the debris that is building up beneath the nail. As a result, the nail will become distorted or deformed in shape. In some cases, the infected nail may separate from the nail bed. This condition is known as onycholysis. Pain in the toes or fingertips may be felt, and a foul odor may emanate from the infection.