Pitted Keratolysis: Symptoms, Types, Causes and Treatment

Pitted keratolysis is a common yet often misunderstood skin condition that predominantly affects the soles of the feet. Characterized by small, crater-like pits and a distinct malodor, this condition can be both distressing and embarrassing for those affected. While not dangerous, its impact on daily comfort and social interactions is significant. In this article, we’ll explore the symptoms, different types, underlying causes, and effective treatments for pitted keratolysis, drawing from the latest research and clinical insights. Whether you’re a healthcare provider, a patient, or simply curious, read on for a comprehensive overview.

Symptoms of Pitted Keratolysis

Pitted keratolysis reveals itself through a handful of distinctive symptoms, primarily affecting the feet. Recognizing these signs early can lead to prompt and effective treatment, minimizing discomfort and social stigma. The symptoms often go beyond the visible pits, including sensory changes and associated skin conditions.

Symptom	Prevalence	Description	Source(s)
Pitted Lesions	Very common	Crater-like pits 1–3 mm wide	1 5 6
Malodor	70–89% of cases	Strong, unpleasant smell	1 3 5 6
Hyperhidrosis	70–90% of cases	Excessive sweating	1 3 5 6
Pruritus	Up to 60%	Itchiness, sometimes burning	5 6
Sliminess	69–70%	Moist, slippery skin feel	1 6
Pain/Tenderness	Occasional	Discomfort on walking	6

Table 1: Key Symptoms

The Pits: Hallmark of the Disease

The most recognizable feature is the appearance of small, shallow pits on the weight-bearing areas of the soles—typically the balls of the feet, heels, and sometimes between the toes. These pits range from 1 to 3 mm in diameter and can number from just a few to over fifty. The affected skin often appears macerated (wet and white), and the pits may gradually coalesce, forming larger erosions or plaques 1 5 6.

Malodor and Sliminess

A strong, unpleasant odor is almost always present, sometimes described as “cheesy” or “sour.” This is often the primary reason patients seek medical attention, as the odor can be socially embarrassing 1 3 5 6. The skin may also feel unusually slimy or slippery to the touch, further distinguishing pitted keratolysis from other foot conditions 1.

Hyperhidrosis and Pruritus

Excessive sweating (plantar hyperhidrosis) is both a symptom and a key risk factor. Up to 90% of cases report significant sweating, which creates the moist environment bacteria need to thrive 1 3 5 6. Itching (pruritus) and, less commonly, a burning sensation can also occur, making the condition uncomfortable as well as unsightly 5 6.

Pain, Tenderness, and Associated Conditions

While pain is not a dominant symptom, some patients experience tenderness or mild pain, especially when walking or standing for prolonged periods 6. Fissuring (cracking) of the soles, concurrent fungal infections, and rarely, conditions like psoriasis or plantar warts may be seen alongside pitted keratolysis 5.

Types of Pitted Keratolysis

Although the general presentation is similar, pitted keratolysis can manifest in slightly different clinical and histological forms. Understanding these can help in diagnosis and may influence management strategies.

Type	Key Features	Typical Location	Source(s)
Superficial	Minor, shallow pits; coccoid bacteria	Upper stratum corneum	6
Classic	Deeper, crater-like pits; coccoid and hyphae	Weight-bearing sole	6
Plantar	Pits, malodor on soles	Balls, heels, toes	3 4 5 6
Palmar (rare)	Ringed lesions on palms	Palms	4

Table 2: Clinical and Histological Types

Histological Types: Superficial vs. Classic

Two main types are recognized histologically:

• Superficial (Minor) Type: Characterized by shallow pits limited to the uppermost layer of the stratum corneum. Here, clusters or chains of coccoid bacteria are typically found.
• Classic (Major) Type: Features deeper, more pronounced pits. Both coccoid bacteria and filamentous (hyphal) structures may be seen, indicating more extensive involvement 6.

Clinical Presentations: Plantar and Palmar Variants

• Plantar Pitted Keratolysis: The commonest form, displaying pits on the soles, especially in pressure and friction areas—the balls of the feet, heels, and toe interfaces 1 3 4 5 6.
• Palmar (Ringed) Keratolysis: Rarely, similar lesions appear on the palms as ring-shaped (annular) keratolysis. This is much less frequent and often seen in people with similar exposure risks 4.

Other Presentations

Some patients may develop plaques, fissures, or annular lesions in addition to pits. In rare cases, the lesions can coalesce, creating larger areas of erosion 6.

Causes of Pitted Keratolysis

Understanding why pitted keratolysis develops is essential for both prevention and treatment. This section breaks down the microbial culprits, environmental triggers, and risk factors behind this distinctive skin infection.

Cause	Description	Typical Risk Factors	Source(s)
Bacterial Infection	Corynebacterium, Kytococcus, Dermatophilus, Streptomyces	Foot moisture, occlusion	4 6 7 8 9 10
Hyperhidrosis	Excessive sweating creates moist habitat	Genetics, footwear, climate	1 3 5 6 10
Occlusive Footwear	Traps sweat and heat	Soldiers, athletes, office	3 6 10
Skin pH & Maceration	Higher pH, softened skin promote bacteria	Poor hygiene, spa treatments	6
Barefoot Exposure	Contact with soil, especially tropical	Farmers, rural workers	1 3 5 9

Table 3: Main Causes and Risk Factors

The Bacterial Agents

Pitted keratolysis is caused by a superficial bacterial infection of the skin’s outer layer (stratum corneum). Multiple bacteria have been implicated:

• Corynebacterium species: The most consistently identified organism in clinical and experimental studies 4 6 10.
• Kytococcus sedentarius (formerly Micrococcus sedentarius): Demonstrated to induce typical lesions when applied experimentally 6 7.
• Dermatophilus congolensis: More common in animal infections but occasionally identified in humans, especially those with soil exposure 6 8 9.
• Streptomyces: Less frequently implicated, but capable of causing similar lesions 6.

These bacteria produce proteolytic enzymes that degrade keratin, forming pits and erosions 6.

Environmental and Personal Risk Factors

The bacteria flourish in warm, moist environments. Key risk factors include:

• Hyperhidrosis: Excessive sweating of the feet is almost universally present and is the most significant individual risk factor 1 3 5 6 10.
• Occlusive Footwear: Boots and synthetic shoes trap heat and moisture, making soldiers, athletes, and office workers particularly vulnerable—even those with good socioeconomic status and hygiene 3 6 10.
• Barefoot Exposure: In tropical or rural settings, barefoot walking increases risk, likely due to increased contact with contaminated soil 1 3 5 9.
• Increased Skin pH and Maceration: A higher pH and softened (macerated) skin facilitate bacterial overgrowth. Spa treatments and poor foot hygiene may exacerbate the problem 6 3.

Demographics

While pitted keratolysis can affect anyone, studies show a male preponderance, especially among young adults and those in professions that require prolonged shoe-wearing or barefoot work 5 6.

Treatment of Pitted Keratolysis

Managing pitted keratolysis involves both eliminating the infection and addressing contributing factors like sweat and footwear. Recent studies offer insights into what works best, from topical antibiotics to practical lifestyle changes.

Therapy	Efficacy	Comments	Source(s)
Topical Antibiotics	High	Clindamycin, erythromycin, mupirocin, fusidic acid	6 11 12 13
Antiseptics	Effective	Chlorhexidine scrub	12
Hygiene Measures	Essential adjunct	Cotton socks, open shoes, foot washing	6 11
Antiperspirants	Useful adjunct	Reduce sweat, aluminum chloride	6 11
Oral Antibiotics	Limited evidence	Only used in refractory cases	11
Other Topicals	Variable	Salicylic acid, sulfur, benzoyl peroxide	6 10

Table 4: Treatment Options and Outcomes

Topical Antibiotic Therapy

• Clindamycin and Erythromycin: Both have shown high success rates as first-line topical agents. Clindamycin 1% gel and erythromycin 4% gel are effective, safe, and well-tolerated 6 11 12.
• Mupirocin: Twice-daily application of 2% mupirocin ointment can resolve lesions within three weeks, with a low recurrence rate 13.
• Fusidic Acid: Also cited as an effective topical antibiotic 11.
• Chlorhexidine Scrub: A cost-effective antiseptic alternative with similar efficacy to topical antibiotics 12.

Supportive Measures

• Foot Hygiene: Daily washing, thorough drying, and use of antibacterial soaps are crucial. Cotton socks and open footwear reduce moisture 6 11.
• Antiperspirants: Aluminum chloride-based antiperspirants help in managing plantar hyperhidrosis, thus preventing recurrences 6 11.
• Lifestyle Modifications: Encouraging patients to avoid occlusive shoes, change socks frequently, and allow feet to air-dry can significantly reduce recurrence 6 11.

Other Treatments

• Salicylic Acid, Sulfur, Benzoyl Peroxide: These keratolytic and antibacterial compounds may be used, though evidence is less robust 6 10.
• Injectable Botulinum Toxin: Rarely used, potentially helpful for intractable hyperhidrosis 6.
• Oral Antibiotics: Reserved for severe or refractory cases; current evidence does not support their routine use 11.

Duration and Prognosis

Treatment typically lasts 2–3 weeks. Recurrence is uncommon if predisposing factors—especially sweating and footwear—are addressed. Education on prevention is vital; otherwise, the condition may return 3 13.

Conclusion

Pitted keratolysis is a common, treatable skin infection predominantly affecting the soles of the feet. Recognizing its distinctive symptoms and understanding the underlying bacterial and environmental causes are key to effective management. The mainstay of treatment is topical antibiotics and improved foot hygiene, but adjunctive measures like antiperspirants and lifestyle changes enhance outcomes.

Key Takeaways:

• Distinctive Symptoms: Crater-like pits, malodor, excessive sweating, and sometimes itch or pain are typical.
• Causative Bacteria: Corynebacterium, Kytococcus sedentarius, and others thrive in moist, enclosed environments.
• Risk Factors: Hyperhidrosis, occlusive footwear, and barefoot exposure are primary contributors.
• Effective Treatments: Topical antibiotics (clindamycin, erythromycin, mupirocin), antiseptics (chlorhexidine), and hygiene measures are most effective.
• Prevention: Addressing sweat and footwear habits can prevent recurrence.

Empowering patients with knowledge and practical strategies ensures this benign but bothersome condition remains well-controlled and rarely recurs.