The Vale Clinic

Fungal nails – Why does the Underside of Toenails Smell bad?

There are several reasons why you might get a ‘bad smell’ from the underside of a toenail.

Here, I will be focusing on one very common reason – fungal nails…

Fungal nails can give off an offensive smell if you’ve ever been brave enough to scrape the muck from underneath the nail.

In the next few minutes, I will be sharing with you:

  • What fungal infection is
  • How you can identify it
  • How and why, you develop a fungal nail infection
  • Treatment and management

If you’ve decided it sounds all too gruesome at this point, you might want to STOP reading here, but if you want to get down to the nitty-gritty about nasty horrible fungi, continue reading, you’ve been warned! mind you some fungus are friendly fungi – mushrooms.

What is a fungus?

Fungi are organisms found in the soil, air and in the water around us, and as a result, infections can start on the skin or in the lungs.

Fungi live on dead tissue, skin, nails and hair, and multiply in warm, moist environments for example, in-between the toes or underneath a nail.

There are different kinds of fungi which cause infection on different parts of the body. On the foot, fungal skin infection is called Tinea Pedis, a.k.a. athlete’s foot.

Majority of individuals who have recurring bouts of athlete’s foot, usually go on to develop fungal nail infection, known as Onychomycosis, quite a mouthful.

Fungal nails are caused by non- dermatophytes (yeasts, moulds) and or dermatophytes that live off the protein on the surface of the skin.  Dermatophytes being the most common to cause fungal nail infections.

How can I tell, I have a fungal skin or nail infection?

Athlete’s foot, can be caused by different strains of fungi, and therefore look different in presentation. 

It can appear as dry scaly or flaking patches of skin, as red itchy spots sometimes filled with pus, and on other occasions, as moist areas in-between the toes, most especially the little toe.  All these, can also occur at the same time, on the same foot.

Fungal nails are not pleasant to look at, in most cases the nail has a white to yellowish discolouration on the surface of the nail. They can have a  crumbly chalky texture,  and a yellowish/cream or black/greenish discolouration of soft sticky mash underneath the nail – this is where the smell usually comes from! 

Streaking within the nail, and lifting of the nail from the nail bed is possible.

The thickness of the nail, can vary from normal to excessively thickened.

Analysing the physical appearance of the nail can only serve as an indication of fungal infection, backed with the observer’s experience – in this case, a Podiatrist, a more accurate diagnosis can be reached.

However, to be absolutely sure of a clinical diagnosis, and before you start any form of treatment, it is recommended a lab test (mycology test) is completed.

mycology test can be requested through your GP to confirm a diagnosis. Lab tests, on average, can take up to six weeks.  An initial report is usually available after two weeks, and the final report at six weeks.

More recently, tests that can be performed on the spot in a clinical setting, are readily available to practitioners. This significantly reduces the time it takes from diagnosing the nail infection, to starting a treatment of choice.

How does it develop, and why?   

According to research, fungal nail infection affects between 2% and 8% of adults in the western world.  The cause for developing fungal nail infections can vary from person to person.

The most common reason is the presence of Athlete’s foot which may well have been long- established on the skin.

Running a marathon is a good example of a sport related activity that can lead to damage to the nail. The nail can be damaged through repetitive injury to the nail in the shoe, weakening the nail plate, rendering it vulnerable to infection.

There are other reasons and conditions that can increase the possibility of developing a fungal nail infection, these include:

Most fungal skin and nail infections are treatable, however, with that said, it will require the 3 Ps-  persistence, patience and perseverance…

    Fungal nail infection or onychomycosis (Tinea unguium) accounts for approximately 50% of nail conditions. 

     It is more common in toenails than fingernails, and can present in four main patterns.

First of all, to help with a bit of terminology, below is a labelled diagram showing he different parts of the nail.


Figure 1: Structure of the nail



Distal -Lateral Sub-ungual Onychomycosis (DLSO)
This is the most common pattern of infection.  The fungus infects the nail from the underside of the nail, and can be caused by any of the organisms – dermatophytes and non-dermatophytes.  The infected nail can vary in colour from brown to black, and can be associated with lifting of the nail, from the nail bed.

Figure 2: DLSO


Superficial Onychomycosis (SO)
Here, the fungus infects the surface of the nail, causing Islands of white discolouration or grooves in the nail.

Figure 3: SO

Total Dystrophic Onychomycosis (TDO)
The whole nail plate is affected, and is characteristic of severe nail infection.  This is usually observed in the latter stages of fungal nail infections, where the nail is thickened and crumbles away.  TDO is caused by different organisms.

Figure 4: TSO
(credit rock- café.info)

Proximal Sub-ungual Onychomycosis (PSO)
This is a rare form of fungal nail infection, and can prove difficult to treat. The infection starts from the half – moon shape at the base of the nail called the lunula.  It is commonly seen in individuals with a suppressed immunity.

Figure 5: PSO

Why should I treat it?

Fungal nail infection can have a significant effect on the quality of life, it can be a source of embarrassment and have a debilitating effect on self-image.

Onychomycosis is common in the elderly, individuals with a lowered immunity, poor circulation and diabetes.

In individuals with lowered immunity or chronic diseases such as Diabetes and poor circulation, it can lead to secondary bacterial skin infection known as cellulitis.

Fungal infection can potentially spread to other parts of the body – hands, groin or torso if left untreated.

Treatment of fungal infections should therefore not be seen as a cosmetic condition discounting the need for treatment, but should be assessed on an individual basis.

Not all individuals will be suitable for treatment.  Suitability is based on the individual’s health status, and suitability to treatment available. The attending clinician will take a thorough medical history to form a basis of whether treatment should be considered.

Below are some questions to be explored when considering treatment –

Is the nail uncomfortable or painful?

Is the appearance of the nail causing embarrassment to the individual?

Is it a potential or likely cause of recurrent skin infection? (especially in individuals with poor circulation or diabetes where their health may be compromised)

Is the individual suitable for any of the proposed treatments?



How do I treat it?

Fungal skin infection and most fungal nail infections can be treated and managed effectively.

Clinical diagnosis of fungal nail infections should be done in conjunction with laboratory findings prior to treatment. 

Once the causative organism/s are known, treatment can be better targeted.  This reduces the risk of unnecessarily creating a huge dent in your bank balance, and save time on your part, as treatments can take several months.

Treatment modalities for fungal nails are systemic or topical preparations. 

Systemic agents come in the form of medicines, and topical agents that can be applied directly to the nail – a paint/lacquer or solution.

Treatment should only be started after consultation with a healthcare professional or general practitioner.

The severity of fungal nail infection is classified depending on the percentage of nail affected, this is simply a guide.

Mild – less than 40% of the nail is affected

Moderate – 40 to 70% affected

Severe– the whole nail is affected


A typical scenario of  the process when diagnosing and treating a fungal nail infection is as follows:

  • An individual attends clinic with a suspected fungal nail infection
  • The Podiatrist confirms clinical evidence of a fungal nail infection, and in some cases accompanying fungal skin infection
  • Nail clippings are taken from the infected nail, and sent  to the laboratory for testing to confirm or discount clinical findings

    Positive laboratory result –

    Start treatment:

    Mild to Moderate infections – The Podiatrist may consider recommending the use of topical treatments or other treatment options such as photo-therapy using low laser therapy.

    Moderate to severe infections – The Podiatrist may consider referring on for systemic medication by careful selection of the patient, plus the use of topical treatment. 

    Nail removal under sterile conditions with local anaesthetic, and treating the nail bed  with an anti-fungal agent afterwards, may also be considered.

    Negative laboratory result –

    Review in clinic with Podiatrist to determine other possible causes of nail damage, and or refer for further investigation/opinion if  indicated.

    It is recommended that any existing fungal skin infection is treated, when starting treatment for fungal nail infections. 

    Check other family members for fungal infection, and have them treat any infections at the same time.

    Athletes foot can be treated with fungicidal creams and sprays – Lamisil is an example.  Follow the manufacturer’s instructions on use, or as directed by your prescriber.

    Most preparations are applied daily, and some once a week.

    Lamisil Once is used once, and over the course of seven days the active ingredient is delivered into the skin killing the fungus. Results are seen very quickly, usually within a few days.


    How can I prevent fungal nail and skin infection?

    After successful treatment of fungal nail and skin infection, the possibility of recurrence is high as a result of the type of lifestyle we live, for example swimming, gym visits all can create the right environment to develop fungal infection in the feet.

    Fungal elements can remain in our immediate environment,  in shoes and socks creating a reservoir and source of re-infection.

    It is therefore important to make sure we unburden our immediate environment of fungal elements by adopting an effective cleaning routine, and treating socks and shoes with anti-fungal agents, or replacing them where possible.

    To reduce the risk of relapse, practise good foot care habits and follow these basic tips:


    • Treat any signs of Athlete’s foot early
    • Check there are no other active sources of infection elsewhere i.e. hands, groin, torso
    • Ensure other family members are free of fungal skin infection.
    • Wash your feet daily
    • Dry feet properly after bathing, particularly in-between toes
    • Protect feet in communal or shared bathing areas
    • Discard old footwear and socks.
    • Wear 100% cotton socks, if possible, replace existing ones
    • Change your socks daily, wear breathable cotton socks
    • Wash socks and towels on a hot wash, 60 degrees
    • Choose footwear made from breathable materials
    • Spray shoes before and after wear, with an anti-fungal spray
    • Alternate your shoes to allow them to air
    • Avoid tight fitting socks and shoes
    • Keep your feet dry throughout the day
    • Keep nails short, clean and dry. This helps prevent infectious organisms from collecting under the nail
    • Sanitise instruments used for nail care by sterilisation after each use
    • Use of a nail lacquer on the nails twice a month as a preventative measure, has been shown to reduce the risk of relapse
    • Use an anti-fungal cream once or twice a month as a preventative measure- if you suffer with frequent bouts
    • Maintain and improve health in chronic conditions (for example – stop smoking, manage diabetes adequately)
    • Visit a Podiatrist or general practitioner for advice and guidance on treatment and management if there is any evidence of recurrence


      Call The Vale clinic today on 07988 916 198 to book an appointment, or to find out more about treatments offered for fungal nail infections.

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