yellow toenails indicating onychomycosis

Toenail Fungus

A toenail fungus infection happens when one or more fungal strains invade your toenails or the skin surrounding your nails. Toenail fungus, called onychomycosis and tinea unguium in the medical world, is a very common infection; about 10 percent of adults in the US experience toenail fungus at some point in their lives. 


What Causes Toenail Fungus

Symptoms of Toenail Fungus

Types of Toenail Fungs

Toenail Fungus Treatment



What Causes Toenail Fungus

Half of all nail disorders reported are caused by onychomycosis, making it the leading nail disorder in adults. Toenail fungus infections occur when yeast or fungal microbes invade through tiny cracks in your nails and skin. Most toenail fungus infections happen when the feet are exposed to fungus in damp, public environments like gyms, locker rooms and swimming pools. However, because fungus thrives in warm, moist environments, feet that aren’t kept clean and dry or feet that are frequently trapped in non-breathable shoes and socks are also vulnerable to developing the infection. People who have dry, brittle nails as well as open wounds near their toenails (ingrown nails, for example) are also more apt to develop nail fungus infections because fungal microbes can more easily penetrate the weakened area. 


Perspiring heavily, working in humid environments (like as a bartender or housekeeper), old age and a suppressed immune system from conditions like diabetes are also factors that increase your risk of developing toenail fungus. 



Onychomycosis usually begins as a small white, yellow, green or black spot under the nail that eventually causes the nail to become discolored, disfigured, thickened, brittle, and crumbly at the edges. Toenail fungus symptoms usually begins as a cosmetic problem only, followed by pain, loss of dexterity, interference with standing and/or walking and paresthesia, which is an abnormal sensation that resembles tingling or pricking. These symptoms will appear on all affected nails, meaning you may only have one nail that shows signs of toenail fungus, or you may have several nails that display these symptoms.


When left untreated, onychomycosis can cause the skin surrounding the nails to become sensitive, scaly and inflamed. The ragged nail can also begin to separate from the nail bed and a foul odor or discharge can be detected. The fungus has the ability to spread to the skin around your nail as well as other nails — including your fingernails.


In some cases, fungus-free skin legions called dermatophytids can develop on other parts of the body. They can be rashes or patches of itchy skin that are essentially your body’s way of letting you know it is allergic to the fungus infecting your nails. 


Each type of onychomycosis produces different symptoms, which are laid out in each of the five main subtype of the fungal condition below.



There are five different types of toenail fungus, including:

1. Distal Lateral Subungual Onychomycosis

Distal lateral subungual onychomycosis is caused by the fungus Trichophyton rubrum and is characterized by a thicking under the nail (called subungual hyperkeratosis), a yellow-whitish nail appearance or yellow streaks on the nails, and a separation of the nail from the nailbed (called onycholysis). Sometimes this type of nail infection causes the nails to erode and become flaky.


2. White Superficial Onychomycosis

White superficial onychomycosis is characterized by small, white, powdery patches on the surface of the nail as well as nails that crumble easily. This type of fungal infection usually affects toenails only; it rarely affects fingernails. 


3. Proximal Subungual Onychomycosis

Proximal subungual onychomycosis is characterized by white spots or lines on the nails that move away from the cuticle as the nail grows. This type of toenail fungus can also cause swelling and inflammation of the skin around the nails. 


4. Endonyx Onychomycosis

Endonyx onychomycosis causes a white discoloration of the nail with no evidence of nail thickening or nail separation.


5. Candidal Onychomycosis

Candidal onychomycosis generally develops in people who have chronic candida (the fungus that causes yeast infections) and is characterized by inflammation and a bulbous appearance of the affected fingernails or toenails. Candidal onychomycosis is extremely tenacious and can quickly infect most or all of the toenails at one time.


People with toenail fungus may have one or a combination of these subtypes infecting their nails at one time. Total dystrophic onychomycosis is the term used for the most advanced form of any subtype and is characterized by a thickened, brown, green or black nail. 



As laid out above, toenail fungus comes in many forms and can look like other conditions, so it is best to get your feet examined by a podiatrist or a dermatologist to receive a trustworthy diagnosis. Most treatment options are long and expensive processes, as the construction of the nail makes onychomycosis very difficult to treat.


Once the specific type of fungal infection is determined, your doctor may prescribe an oral antifungal like itraconazole or fluconazole, or a topical cream such as terbinafine or ciclopirox that is applied directly on the nail. However, because topical creams cannot fully penetrate the nail and rarely cure onychomycosis on their own, they’re usually given in combination with oral antifungals.


Toenail fungus treatment can be difficult, as the infection is often embedded in the nail and difficult to reach. Treatment procedures can last several months — sometimes up to a year — as new nail growth must entirely replace the infected area. Up to 50% of toenail infections reoccur, and in some cases, partial or full nail removal may be necessary. Severe cases of toenail fungus can cause permanent damage and can spread to other areas of your body, especially if you have a weakened immune system or diabetes. 


Another treatment option for onychomycosis is laser toenail fungus removal, but this process is quite expensive and is still considered experimental. For more on laser toenail fungus removal, read these pros and cons of laser toenail fungus removal. You may also want to read our list of home remedies for toenail fungus that can help slow the spread of the infection and in some cases can cure toenail fungus altogether.


People with diabetes who believe they have a fungal infection should seek help from a health care provider, as the infection could lead to serious health complications.  

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Articles having medical content shall serve exclusively for the purpose of general information. Such articles are not suitable for any (self-) diagnosis and treatment of individual illnesses and medical indications. In particular, they cannot substitute for the examination, advice, or treatment by a licensed physician or pharmacist. No replies to any individual questions shall be effected through the articles.

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