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What is Onychomycosis?

Onychomycosis is an increasingly common disorder, accounting for 20% of all nail diseases. It occurs almost exclusively in adults and one in two people over the age of 70 suffers from it. The risk therefore increases with age and through underlying nail disease. 


Disease overview


Onychomycosis is an infection of the nails caused by a fungus. Symptoms of the infection will vary depending on the type of fungus involved, but thickened nails and yellow discoloration are common.

Approximately one half of all nail conditions are the result of fungus, making onychomycosis the most common nail disorder. A large survey estimated that as many as 16% of Europeans may have fungal nail infections. Onychomycosis can affect both the fingernails and toenails; however the toenails are more likely to be involved. The reasons for this are not entirely clear, but the slower growth of toenails, prior fungal infection of the feet (called athlete’s foot) may make it easier for fungi to establish themselves and cause an infection of toenails. As well, fungi typically thrive in warm, moist conditions. Closed and plastic shoes are therefore ideal environments for these organisms, making it easier for them to infect the feet and toenails. Walking barefoot in locker rooms also increases the risk of infection, as this hot and humid environment is susceptible to fungal contamination. Fingernails can also be infected, often by another type of fungus. Often these types of infections occur in people whose hands have been exposed to water for long periods of time, for example dishwashers in restaurants or professional house cleaners. Wearing double gloves – cotton on the inside and latex or vinyl on the outside – when in contact with water helps to prevent against developing these types of infections.


Your doctor will likely start an examination by simply looking at your nails. Different types of onychomycosis have characteristic features that suggest fungal nail infection, and these can be used to differentiate onychomycosis from other types of infection. There are additional laboratory tests that are used to confirm the diagnosis. Looking at sections of nail under a microscope can sometimes be used to directly visualize the fungi that cause the disease. As well, if fungi can be grown in the laboratory from samples and scrapings of nail, this is evidence that fungi are responsible for the disease. Often a doctor will make a preliminary diagnosis based on examining the nails and confirm this in the laboratory using microscopy and culture techniques. It might be a few weeks before your doctor gets the results of the laboratory tests.



  • Onychomycosis is a type of nail infection caused by pathogenic fungi.
  • Approximately half of nail conditions are onychomycosis, making it the most common nail disorder.
  • Both fingernails and toenails can develop fungal infections, but toenails are more commonly affected.
  • Doctors use a combination of clinical examination and laboratory tests to successfully differentiate onychomycosis from other types of disease.

Risk Factors

Not everyone has the same risk of developing fungal nail infections. Studies have shown that there are several factors that increase the risk of common onychomycosis infections: Tosti 2005


The risk of developing onychomycosis increases with age. This may be because older people have slower growing nails, have difficulties taking care of their feet and toenails and are more likely to have other risk factors for the disease (poor peripheral blood circulation, diabetes, weakened immune state)

Poor peripheral blood circulation

People with poor peripheral blood circulation are more susceptible to fungal infections


Diabetes has several effects on the circulatory system, and has been shown to increase the risk of developing onychomycosis


Onychomycosis is more common in people who have psoriasis than those who do not.


Some sports may increase exposure to pathogenic fungi and therefore increase the risk of fungal infection. People who swim, for example, are more likely to have onychomycosis than those who do not.


As with other types of infection a weakened immune system increases the risk of developing onychomycosis.

Genetic factors

Some people seem to be naturally more susceptible than others to fungal infections such as onychomycosis. The exact genes involved have not been identified, but some research suggests that you are more likely to develop fungal nail infections if you have a family history of the disease.

Cases of fingernail onychomycosis have a slightly different set of risk factors, including: Tosti 2005

  • Prolonged contact with water
  • Prolonged wear of plastic gloves
  • Frequent or prolonged manipulation of sweet products (candy, pastry)
  • Excessive use of detergents
  • Smoking
  • Repeated microtrauma to nails (e.g. gardening)
  • Exposed profession (hairdresser, manicurist, podologist)
  • Other sites of fungal infection


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Este é um site Global, voltada para educar o público e os pacientes sobre as condições da pele e os diferentes tipos de tratamentos que estão disponíveis para tratar e controlar essas doenças. Este site não pretende ser um substituto para aconselhamento do seu médico, e pode incluir discussões sobre terapias ou opções de tratamento que podem não estar disponíveis no seu país. Nós encorajamos você a usar as informações contidas neste site para educar-se sobre a sua doença e permitir uma melhor comunicação entre você e seu profissional de saúde.


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