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What is this tiny hole in the foot

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The tiny holes/pits in your foot image are most consistent with Pitted Keratolysis - a superficial bacterial skin infection of the sole. Here's a full breakdown:

Pitted Keratolysis

The image shows multiple small, pinpoint dark pits scattered across the weight-bearing heel area. This pattern - tiny crater-like depressions in thick plantar skin - is the classic presentation of pitted keratolysis.

Here is what a more advanced case looks like for comparison (your image appears to be an early/mild stage):

Pitted Keratolysis - classic appearance showing multiple crater-like pits across the entire sole

Fig. 14.26 Pitted keratolysis - Andrews' Diseases of the Skin

What causes it?

It is a non-inflammatory bacterial infection of the stratum corneum (outer skin layer). The main culprit is Kytococcus sedentarius, though Corynebacterium spp., Dermatophilus congolensis, and Actinomyces spp. can also cause it. These bacteria produce serine proteases that literally digest and pit the keratin in the thick foot skin. Sulfur-containing compounds released during this process cause a characteristic bad smell. - Dermatology 2-Volume Set 5e

Who gets it?

Adult males with sweaty feet (~90% of cases, male-to-female ratio strongly skewed)
People in hot/humid climates, or those who wear occlusive footwear for long hours (athletes, soldiers, workers)
Predisposing factors: hyperhidrosis (excessive sweating), prolonged occlusion, elevated skin surface pH - Fitzpatrick's Dermatology

Clinical features

Small (1-7 mm), crater-like pits on weight-bearing soles - heel, ball of foot, toes
Pits may coalesce into larger craters or rings
Usually no pain or itching
Often noticed because of bad foot odor rather than visible lesions
No redness or inflammation around the pits

How to distinguish it from plantar warts

Feature	Pitted Keratolysis	Plantar Wart
Skin lines	Intact - run through the lesion	Disrupted - lines go around it
Dots	Shallow dark pits	Thrombosed capillaries (bleed when pared)
Cause	Bacteria	HPV virus
Number	Multiple, scattered	Often single or clustered
Wood's lamp	No fluorescence	No fluorescence

Treatment

Good news - it responds quickly to simple topical treatments (Andrews' Diseases of the Skin):

First-line topicals: Erythromycin, clindamycin, or mupirocin cream/gel applied twice daily
Alternatives: 5% benzoyl peroxide gel, miconazole/clotrimazole cream
For sweating: 20% aluminum chloride solution to control hyperhidrosis
Hygiene: Keep feet dry, use antibacterial soap, change socks frequently, avoid occlusive footwear when possible
Stubborn cases: Oral clarithromycin (single dose), or botulinum toxin if hyperhidrosis is severe

Most cases resolve within 1-2 weeks of topical treatment.

Note: This is a visual assessment only - a dermatologist or podiatrist can confirm the diagnosis in person. If the spots are painful when pressed, cause bleeding when pared, or disrupt the normal skin ridge pattern, a plantar wart should be considered instead.

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I now have comprehensive material from both Andrews' and Fitzpatrick's. Here is the full treatment guide:

Foot Lesion Treatment Guide

Pitted Keratolysis & Plantar Warts

How to Tell Them Apart First

Before treating, confirm which condition you are dealing with - they look similar but have very different causes and treatments.

Feature	Pitted Keratolysis	Plantar Wart
Cause	Bacterial (Kytococcus sedentarius, Corynebacterium spp.)	HPV types 1, 2, 27, 57
Appearance	Multiple tiny crater-like pits, may coalesce	Firm, raised papule with central pulpy core
Skin ridge lines	Intact - lines run through the lesion	Disrupted - lines go around the lesion
Black dots	Shallow dark pits (bacterial activity)	Thrombosed capillaries (bleed when pared)
Pain	Usually none; 1/3 have burning/irritation	Often painful with walking
Odor	Characteristic bad smell (~2/3 of cases)	None
Slimy feet	Yes - foot sticks to socks (~70% of cases)	No
Location	Heel, ball, toe pads (weight-bearing areas)	Ball of foot, midmetatarsal area; can be anywhere on sole
Wood's lamp	No fluorescence	No fluorescence

PART 1: PITTED KERATOLYSIS

What Is It?

A superficial, non-inflammatory bacterial infection of the stratum corneum (outer skin layer) of the plantar foot. The bacteria produce serine proteases that digest keratin, creating crater-like pits. Sulfur compounds released in this process cause the characteristic malodor. - Fitzpatrick's Dermatology, Vol. 1-2

Most susceptible: Adult males with hyperhidrosis (~90% of cases, male:female ratio ~8:1). Hot, humid climates and occlusive footwear are key risk factors.

Step 1: Confirm the Diagnosis

Diagnosis is clinical - the appearance alone is usually enough
Gram stain of skin scrapings can detect the organisms
Bacterial culture is not helpful (multiple species grow out)
Biopsy is rarely needed; if done, Gram/PAS/methenamine silver stains show cocci and filamentous bacteria in pit walls

Step 2: Control Hyperhidrosis (Root Cause)

Keeping the feet dry is the most important step. Without this, the condition will recur even after antibiotic treatment.

Agent	How to Use
Aluminum chloride 20% solution	Apply to dry skin at night; first-line antiperspirant for feet
Topical glycopyrrolate	Applied topically for localized hyperhidrosis
Botulinum toxin (Botox)	Injected into soles for severe/recalcitrant hyperhidrosis; highly effective but requires a specialist
Absorbent foot powder (inert antiseptic)	Daily use in socks and shoes to absorb moisture

Step 3: Topical Antibiotics / Antimicrobials

These are curative in the majority of cases. Apply twice daily for 2-4 weeks.

Agent	Type	Notes
Erythromycin 2% solution/gel	Topical antibiotic	Highly effective, first-line
Clindamycin 1% solution/lotion	Topical antibiotic	First-line alternative
Mupirocin 2% cream	Topical antibiotic	Effective; good for localized areas
5% Benzoyl peroxide gel/cleanser	Antimicrobial	Effective; also helps with odor; apply as wash or leave-on
Fusidic acid cream	Topical antibiotic	Used as adjunctive agent
Miconazole or clotrimazole cream	Azole antifungal	Effective; useful if concurrent tinea pedis is suspected
Aluminum chloride 10-20%	Drying + antimicrobial	Can be used alongside antibiotics

Tip: Combining a topical antibiotic with a keratolytic enhances drug penetration into the thickened stratum corneum.

Step 4: Keratolytics (for thickened/hyperkeratotic skin)

Add a keratolytic to soften the thick overlying stratum corneum and improve antibiotic penetration:

Urea cream (10-40%) - softens and exfoliates thickened skin
Salicylic acid 5-20% - peels away stratum corneum
Lactic acid cream - gentle keratolytic, good for daily use

Step 5: Systemic Antibiotics (Severe/Recalcitrant Cases Only)

Reserve for widespread involvement or failure of topical treatment after 4-6 weeks:

Clarithromycin - single dose (reported effective)
Erythromycin oral - 2-week course
Clindamycin oral - short course

Prevention & Hygiene Protocol

This is as important as treatment to prevent recurrence:

Change socks daily - wash socks at 60°C (140°F) minimum to kill bacteria
Change shoes regularly - allow shoes to fully dry between wearings; alternate pairs
Avoid occlusive footwear (rubber-soled, non-breathable shoes) as much as possible
Wear moisture-wicking socks (synthetic or wool, not cotton)
Dry feet thoroughly after bathing, especially between toes
Antibacterial soap for feet during bathing helps reduce recurrence
Foot powder in shoes daily

Expected Timeline

Symptoms improve within 1-2 weeks of topical treatment
Full resolution: 3-4 weeks with consistent treatment
Without hyperhidrosis control: high likelihood of recurrence

PART 2: PLANTAR WARTS (Verruca Plantaris)

What Is It?

A viral skin infection caused by Human Papillomavirus (HPV) types 1, 2, 27, and 57. The virus causes keratinocyte proliferation, forming a firm, hyperkeratotic papule on the sole. Plantar warts are notoriously more resistant to treatment than warts elsewhere. - Andrews' Diseases of the Skin, Clinical Dermatology

Key point: Many plantar warts, especially in children under 12, will resolve spontaneously without treatment. No treatment is a valid option to discuss.

Indications to treat: Pain, interference with walking, social embarrassment, or risk of spreading.

Therapeutic Options (Stepwise)

TIER 1 - Patient-Applied / Conservative (Start Here)

A. Salicylic Acid (10-26% OTC solutions, 40% prescription pads) Best evidence for patient-applied therapy.

How to use:

Soak affected area in warm water for 5-10 minutes
Gently file dead skin with pumice stone, emery board, or table knife (clean between uses)
Apply salicylic acid solution or gel; allow to dry
Cover with a strip bandage or occlusive tape for 24 hours
Repeat daily
Continue for at least 3 months - do not stop too early

Efficacy: Some studies show parity with cryotherapy; others show it to be inferior. Results are better with consistent application and mechanical debridement.

B. Occlusive Tape (Duct Tape)

Modest evidence; inferior to cryotherapy in adults
Keep wart covered 6.5-7 days/week with a relatively impermeable tape
Best reserved for: children under 12 (high spontaneous resolution rate) or patients refusing other treatments
Adults: only ~20% resolve with 2 months of tape; 75% of "resolved" warts recur

TIER 2 - In-Office Procedures

A. Cryotherapy (Liquid Nitrogen) - First-line in-office treatment

Cure rate: 20-50% with repeated applications
Method: Sustained 10-second freeze with spray gun; freeze to produce 2-3 mm halo around wart
A blister should form 1-2 days after treatment (this is the goal)
Freeze-thaw cycle: a single cycle may be as effective as two
Repeat every 2-3 weeks, just as the old blister peels off
Liquid nitrogen (lower temperature) is preferred over other cryogens
Side effects: Pain (can be significant for several days), hypopigmentation, scarring (rare), nerve damage if frozen too deeply at digit sides
Contraindications/caution: Fanconi anemia, cryoglobulinemia, Raynaud phenomenon, poor peripheral circulation (severe blistering risk)

B. Cantharidin (0.7% cantharidin / "cantharone")

Applied in office, covered with occlusive tape for 24 hours (or until burning)
Blister forms in 24-72 hours (can be very painful)
Repeat every 2-3 weeks
Advantage: Painless to apply - good for children
Disadvantage: Can produce "doughnut warts" (ring-shaped recurrence)

C. Intralesional Candida Antigen Injection

Inject 0.1 mL into 1-3 lesions; repeat every 3-4 weeks
Cure rate up to 80% with multiple treatments; highly effective
Works by triggering local immune response that generates systemic HPV immunity
Side effects: Fever, chills, flu-like symptoms 6-8 hours post-injection (cytokine-mediated); resolves within 24-48 hours. Advise patients in advance.

TIER 3 - Immunologic Therapy

A. Topical Sensitizers (DNCB, Squaric Acid Dibutyl Ester, Diphencyprone)

Patients sensitized at distant site (inner upper arm) first, then applied to warts
Two protocols: high-concentration in-office (2-5% every 2 weeks) vs. take-home lower concentration (0.2-0.5% up to daily)
Keep covered 24 hours after application
Wart resolution begins in 1-2 weeks but typically requires 2-3+ months
Overall cure rates for all three sensitizers: 60-80%
Side effects: Local itch, pain, mild eczema; usually no functional limitation

B. Oral Cimetidine (25-40 mg/kg/day)

Anecdotally reported to help via immunomodulatory effects
Single-agent efficacy is low (~30%, similar to placebo)
May be useful as an adjunct to immunotherapy when response is sluggish
Limited side effects

C. Imiquimod

Evidence for common/plantar warts is weak - cure rates ~10%, comparable to placebo in controlled trials
Not routinely recommended for plantar warts

TIER 4 - Surgical / Laser (Refractory Cases Only)

Use when multiple in-office treatments over 3+ months have failed.

A. Pulsed Dye Laser (PDL)

High fluences (12.5-15 J/cm², mean 14 J/cm²) with 1.5 ms pulse duration, 7 mm spot
Extends 2 mm beyond visible wart margin
Local anesthesia required in most patients
Skin turns gray-black immediately; eschar forms over 10-14 days
Repeat every 2-4 weeks as eschar falls off
Efficacy for refractory warts: 70-90% in immunocompetent patients
Also works for periungual warts (penetrates nail plate)

B. CO2 Laser

Requires local anesthesia; produces scarring and may cause nail dystrophy
Efficacy: 56-81% for refractory warts
Produces potentially infectious plume - appropriate precautions required

C. Surgical Ablation

Last resort; even complete excision of wart + surrounding skin does not guarantee non-recurrence
Reserve for warts refractory to all conservative approaches

D. Bleomycin Injection (1 U/mL)

Injected into wart until blanching; or multipuncture technique (Shelley method)
Reserved for recalcitrant common warts in adults
High efficacy but significant local side effects

Special Considerations

Children under 12: Spontaneous resolution is common. Favor watchful waiting, duct tape, or salicylic acid first. Aggressive cryotherapy should be used cautiously.

Immunocompromised patients: Warts are more extensive, more resistant to treatment, and require more aggressive/longer management. Risk of HPV-induced malignancy is higher - monitor closely.

Mosaic warts (multiple confluent warts): More resistant to all treatments. Require combination approaches and longer treatment duration.

When to Refer

No response after 3 months of consistent treatment
Wart disrupting normal function or gait
Immunocompromised patient with extensive warts
Any lesion with atypical appearance (ulceration, marked bleeding, unusual growth) - biopsy to rule out malignancy, particularly epithelioid sarcoma

Sources: Andrews' Diseases of the Skin: Clinical Dermatology | Fitzpatrick's Dermatology, Vol. 1-2 | Dermatology 2-Volume Set 5e (Elsevier)

So this look like pitted keratolysis

Yes, based on the image, pitted keratolysis is the most likely diagnosis. Here's why it fits:

What matches in your photo:

Multiple tiny, pinpoint dark pits scattered across the weight-bearing heel area
Located on the pressure-bearing zone of the sole (classic location)
The surrounding skin ridges appear intact - they run through and around the spots, not disrupted by them
No raised edges or firm papule (which would suggest a wart)
Mild skin thickening (hyperkeratosis) typical of the heel

What would confirm it further - ask yourself:

Do your feet sweat a lot or feel slimy/stick to socks? (70% of cases)
Is there a bad smell from the feet, especially after taking shoes off? (2/3 of cases)
Do you wear closed, occlusive footwear for long hours?
Any burning or irritation on the sole? (about 1/3 of patients)

If you're answering yes to 2 or more of those, pitted keratolysis is very likely.

Your next step is straightforward:

Start 5% benzoyl peroxide gel (available OTC) - apply to the heel once or twice daily after washing
If you can get a prescription, clindamycin 1% or erythromycin 2% solution applied twice daily clears it faster
Use aluminum chloride 20% at night if your feet sweat heavily
Keep feet dry - change socks daily, let shoes air out, wash socks at 60°C

Most people see clear improvement within 1-2 weeks. A dermatologist or podiatrist can confirm in person if you want certainty before starting treatment.

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