What Is Pitted Keratolysis?

Introduction

This article will investigate the clinical presentation, causes, and prognosis of pitted keratolysis, which is a bacterial skin infection that commonly affects the feet. Pitted keratolysis can be recognised by its pitted appearance on the skin, and often affects feet which are hot, sweaty, and humid.¹ This may be in warmer climate areas or among athletes, farmers, and soldiers.

Causes and risk factors

Pitted keratolysis is a bacterial infection that most commonly affects the superficial skin on the soles of the feet.¹ However, in rare cases, pitted keratolysis can also affect the skin of the palms of the hand or the webbing between fingers and toes. This infection is caused by bacteria such as Corynebacteria, Actinomyces, Micrococcus sedentarius, or Dermatophilus congolensis.^1,2 Bacteria which cause pitted keratolysis are “gram-positive”, meaning that they are generally responsive to antibiotic treatment.

There are several risk factors which can drastically increase your chance of developing pitted keratolysis. Warm, moist environments are optimal for the bacteria that cause pitted keratolysis and allow them to grow and multiply quickly. As such, warm and humid environments can contribute to the development of the infection.³ By extension, wearing footwear that is not breathable or well-ventilated may also increase sweating and temperature of the foot, increasing the chance of bacteria proliferating on the skin.² Any factors leading to increased warmth and moisture increase the chances of pitted keratolysis developing. 

Some people are affected by a condition known as ‘hyperhidrosis’, which is a technical term for excessive sweating. This increases moisture on the skin, and people affected by hyperhidrosis may also be at increased risk of developing skin infections like pitted keratolysis. Similarly, poor foot hygiene or the ability to dry the feet could lead to a warm and moist environment, which can allow the bacteria to multiply.²

As pitted keratolysis is caused by bacterial infection, any condition or medication which suppresses the immune system can expose an individual to a higher risk of infection. This might be HIV/AIDS, chemotherapy or immunosuppressant medication (such as that taken after an organ transplant).³

Clinical presentation

The main symptom of pitted keratolysis is the appearance of whitish-grey pits on the soles of the feet. They can vary in size and shape but tend to cover large areas of the foot. The surrounding skin may also exhibit some toughness or peeling.^2,4

Pitted keratolysis can also result in a strong and unpleasant odour of the feet. This is caused by the by-products of the infecting bacteria.² The infected feet may also sweat more, which can, in turn, result in more proliferation of the bacteria and worsen the problem.⁵ The feet may also become itchy and uncomfortable, especially in affected areas.

Diagnosis

Pitted keratolysis can often be diagnosed by the characteristic whitish-yellow appearance of the skin with many small holes or craters in the sole of the foot. It is often accompanied by a foul odour.⁸ From these signs, a medical professional may be able to begin to order further tests to confirm the presence of the condition.

The medical professional will also ask questions about the patient’s lifestyle and medical history. Certain lifestyle factors, professions, and activities are associated with warm, moist feet and thus increase the chance of developing pitted keratolysis.⁸

To aid in diagnosis, a UV light can be shone onto the affected area in a test known as Wood’s Lamp. This test, when used on infected feet, will show a reddish glow caused by the bacteria that cause pitted keratolysis, producing compounds known as porphyrins.⁹

If a clear diagnosis can still not be made with the available tests, a sample of the infected skin will be sent to the lab. Laboratory tests can determine which bacteria are present in the infection and whether it is one of the bacteria that cause pitted keratolysis. This can lead to a certain diagnosis.

There are other common skin conditions affecting the feet that must also be ruled out when diagnosing pitted keratolysis, including athlete’s foot, tinea pedis, eczema, contact dermatitis, plantar warts, psoriasis, and calluses.⁶ All of these conditions have distinct clinical presentations and pathology, but some of their symptoms may overlap. Consequently, pitted keratolysis must be carefully diagnosed to ensure that the best course of treatment can be employed without delay.⁷

Treatment options

Pitted keratolysis is formed by bacteria and, as a result, is very responsive to treatment with antibiotics. The antibiotics are commonly applied topically and directly to the infected area. The most common and effective antibiotics used to treat pitted keratolysis are clindamycin and erythromycin.¹⁰

In conjunction with the antibiotics, it is important that you maintain good foot hygiene, taking care to reduce heat and moisture around your feet whilst the infection improves.10 It’s important to thoroughly wash and properly dry their feet regularly and avoid prolonged exposure to moisture. This may be done by avoiding footwear such as rubber boots, which do not allow for ventilation, or avoiding environments where the feet are submerged in water for long periods, like some areas of outdoor farming, for example. This objective can be aided by breathable shoes and moisture-wicking socks.

Prevention strategies

Pitted keratolysis is a bacterial infection that can be avoided, and the risks can be mitigated as much as possible. Its prevalence is especially high in workplaces where workers such as farmers, athletes, and soldiers spend long periods on their feet, in moist conditions, or wearing poorly ventilated shoes. One of the key prevention strategies for pitted keratolysis is, therefore, choosing appropriate footwear that allows air to get into the shoe, provides good ventilation, and minimises sweat and temperature build-up. Absorbent socks can also be used to help wick away moisture from the skin to try and minimise bacterial proliferation on the skin.¹¹

You can further reduce your risk of infection by keeping your feet clean and dry, washing and drying them regularly, and not allowing moisture to build up. Good foot hygiene will minimise the build-up of any bacteria, not just those which cause pitted keratolysis, and will help to lower your risk of developing a whole host of infections.¹¹

Finally, another useful method to mitigate and reduce the risk of bacterial infections is rotating footwear. Wearing the same footwear too regularly can allow bacteria to build up in the shoe, whereas rotating footwear can allow the shoes to ventilate and dry between uses. This can prevent bacterial spread and reduce your risk of a pitted keratolysis infection.

Prognosis

The prognosis of a pitted keratolysis infection is generally very good, and the infection is not linked with serious or long-lasting health conditions.² Pitted keratolysis is, therefore, not a dangerous infection in itself, but it can recur and cause further complications down the line if it is not properly treated. As a result, early treatment options will result in quicker resolution of the condition, and upon improvement of the condition, following recurrence prevention strategies is important. This includes improving foot hygiene, drying feet, improving foot ventilation, and rotating footwear.

Potential complications

If left untreated, pitted keratolysis infection, although not harmful in itself, could potentially lead to complications. The infected skin may be more susceptible to infections with other bacteria or fungi, which could cause complications in treatment and lead to added discomfort, pain, and disruption to everyday activities.¹²

Cellulitis is an infection of the deeper levels of the skin, often due to a cut, wound, or damage to the skin, in contrast to pitted keratolysis, which infects the superficial layers of the skin. However, in rare circumstances, if pitted keratolysis causes sufficient damage to the superficial layers of skin, bacteria may be able to reach deeper layers of the skin and cause cellulitis - a much more serious condition.¹³

Summary

Pitted keratolysis is a bacterial infection with a certain type of bacteria, most commonly with Corynebacteria, Micrococcus sedentarius, or Dermatophilus congolensis. It has a generally favourable prognosis and, when treated quickly and fully, responds well to antibiotics. Pitted keratolysis commonly infects the soles of the feet, as the bacteria thrive in warm and moist environments. As a result, preventing bacterial build-up, wicking away moisture, and maintaining good foot hygiene can be effective prevention strategies against infection. This can be done, for example, by using well-ventilated footwear, rotating shoes, and adequately washing and drying feet.  

It is vital to seek medical assistance as soon as you suspect a pitted keratolysis infection. This is because, although the prognosis of the condition itself is favourable, if left untreated, pitted keratolysis can lead to complications such as other infections and abscesses, which are much harder and more invasive to treat. Therefore, prevention and early intervention are of paramount importance in battling this condition.