Nail fungus causes

Nail fungus infection, or onychomycosis, is the most common nail disorder and is responsible for about 50 percent of all nail infections.1

Do you know what is causing nail fungus? As the name implies, the disease is caused by fungi – tiny parasitic organisms that are neither a plant nor an animal. Fungi thrive where it is moist and warm, and feed off of keratin, which is the main protein in your nails, hair and skin. Nail fungus causes overproduction of keratin in the nails, which makes them thicken and separate from the nail bed. 

Your feet harbor nearly 200 types of fungi – more than anywhere else on your body – but not all of them are harmful. The main two types of fungi that cause nail infections are dermatophytes and yeasts. Dermatophytes are usually the culprits behind nail fungus in temperate parts of the world, whereas yeasts are more prevalent in the tropics and are more likely to cause infections of the fingernails. There are many different yeasts that can cause onychomychosis of the fingernails, but most cases are a result of Candida albicans, the same yeast that causes vaginal thrush. Mold is another common cause for fungal infections in tropical areas.

Nail fungus toenail discolored

Risk factors for nail fungus

Nail fungus typically follows a fungal infection of the skin or results from damage to the nail, but certain diseases that suppress the immune system can also put you at greater risk. 

  • Fungal skin infection. Athlete's foot, which causes the skin between your toes to become itchy, red and flaky, is a common cause of nail fungus infections. Of all people who have athlete's foot, approximately one third become infected with a nail fungus as well. Both athlete's foot and onychomychosis are caused by dermatophytes and the infection can easily spread from the skin to the toenails.
  • Damaged nail or skin. Nail biting, repeated trauma, old injuries and tiny cuts in the skin around the nails can also increase the risk of fungal infection. Your cuticles may also become damaged and more susceptible to onychomychosis if you keep your hands in water for long periods of time, for example if your job involves washing a lot of dishes by hand.
  • Exposure to moisture and humidity. Fungi love warm and moist environments and they thrive in swimming pools and showers. In fact, swimmers are three times as likely to contract the disease compared with the general population. Nail fungus is also contagious, so using public showers and walking barefoot across the floor in a locker room puts you at risk for contracting it from other people.
  • Tight footwear. Onychomychosis is more common in the toenails than in the fingernails, partly because the dark, moist and warm environment in your shoes provides the perfect breeding ground for fungi. Shoes also restrict circulation in the feet, which makes it harder for the immune system to detect and fight the infection. Wearing tight-fitting, sweaty shoes while subjecting the toenails to constant trauma is probably one reason why athletes are disproportionally affected by fungal infection.
  • Diseases and medications. If your immune system is weakened due to illness or use of medications such as steroids or antibiotics, you are more vulnerable to a fungal infection of the nails. Psoriasis, inflammatory bowel disease, AIDS, diabetes, cancer or poor circulation have been linked to an increased risk for nail fungus infections.
  • Age. Onychomychosis becomes more prevalent with age and among people over the age of 60, several people may suffer from it. This is likely due to the fact that seniors have poorer circulation and thicker nails that take longer to grow out.
  • Family history. Nail fungus is not hereditary but your genetic makeup can either make you more susceptible to the infection or more apt to fight it. If one family member has onychomychosis, others may also contract the disease from using the same shower or sharing personal items like towels.
  • Other factors. Smoking, using artificial nails and sweating excessively have been associated with an increased risk of nail fungal infection. It is also more common among men than women.


1 Thomas J et al. J of Clinical Pharmacy and Therapeutics 2010:
35; 497-519

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