By the end of this lesson, the learner will be able to:
Differentiate among calluses, corns (hard and soft), and heel fissures based on appearance, location, and clinical findings.
Distinguish a corn from a verruca (plantar wart) using bedside features.
Describe the pathophysiology of pressure-induced hyperkeratosis and the biomechanical and footwear factors that drive it.
Apply evidence-based conservative nursing management and identify when sharp debridement, salicylic acid, or referral are appropriate or contraindicated.
Recognize the elevated risk hyperkeratosis represents in patients with diabetes or peripheral artery disease.
Hyperkeratotic conditions are the foot's response to mechanical stress — the skin thickening to protect itself against repeated friction or pressure. Most of the time this protective response is helpful. When it becomes excessive, painful, or develops in a patient with diabetes or vascular disease, it crosses from adaptation into pathology. This lesson covers the three forms nurses see most often: calluses, corns, and heel fissures.
Why the Skin Thickens
Hyperkeratosis follows a predictable cycle. Understanding it explains both why these lesions form and why removing them without addressing the underlying pressure source guarantees recurrence.
The Pressure Hyperkeratosis Cycle
TriggerRepeated friction or focal pressure
→
AdaptationEpidermal hyperkeratosis to protect underlying tissue
PathologyPain, fissuring, or — with neuropathy — pre-ulceration
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Foundational Principle
Treat the lesion AND the cause. Paring or filing without identifying and addressing the source of pressure — footwear, gait, bony prominence, deformity — produces recurrence within weeks.
Calluses vs. Corns vs. Heel Fissures
The three conditions look similar at first glance and are often confused. The clinical differences below drive the differential.
Side-by-Side Comparison
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Callus
Tyloma — diffuse
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Suggested photo: plantar callus under the 1st metatarsal head
What it isDiffuse thickening of the epidermis from broad, repeated pressure or friction.
Distinguishing featureNo central core; broad area; preserves dermatoglyphic skin lines.
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Corn
Heloma — focal
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Suggested photo: hard corn on dorsum of 5th toe; soft corn between 4th and 5th toes
What it isFocal hyperkeratosis with a central translucent core that can press on nerves.
WhereHard corn: dorsum of toes (shoe pressure). Soft corn: between toes (4th web space most common).
Symptoms
Focal
Painful
Central core
Tender on direct pressure
Distinguishing featureTranslucent central nucleus; sharply demarcated; pain on direct pressure.
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Heel Fissure
Cracked heel
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Suggested photo: heel fissure with surrounding hyperkeratotic rim
What it isVertical splits in thickened, dry skin at the heel margin; can extend into the dermis.
WherePosterior or lateral heel rim; the weight-bearing perimeter of the heel pad.
Symptoms
Linear cracks
Dryness
Pain with weight-bearing
May bleed
Distinguishing featureVertical fissures arising in xerotic, hyperkeratotic skin; deep cracks are an infection risk.
Quick Differentiation: Corn vs. Callus vs. Verruca
A common bedside confusion: is this a corn, a callus, or a plantar wart (verruca)? Treatment differs significantly. Use these four features to differentiate.
Feature
Callus
Corn
Verruca (Wart)
Distribution
Diffuse
Focal, with core
Focal, often clusters
Skin lines through lesion
Preserved
Preserved
Interrupted
Pinpoint black dots
No
No
Yes (thrombosed capillaries)
Pain pattern
Mild, with pressure
Direct pressure ("pinch")
Lateral squeeze ("squeeze")
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Clinical Pearl
"Pinch vs. squeeze" is the fastest bedside differentiation between a corn and a verruca. Corns hurt when pressed straight down. Verrucas hurt more when pinched from the sides. Skin lines are the second tell: a callus or corn preserves them; a verruca disrupts them.
Where They Show Up
Location follows pressure. Knowing the typical sites helps confirm the diagnosis and points to the underlying mechanical cause.
1
1st metatarsal head callusBears the most pressure during push-off; very common in normal gait.
2
5th metatarsal head callusSuggests lateral pressure from gait pattern or footwear that's too narrow.
3
Plantar heel callusOften associated with open-back footwear or chronic dryness.
4
Soft corn between 4th & 5th toesMacerated, painful — caused by interdigital pressure from narrow toe boxes.
5
Hard corn on dorsum of 5th toeFrom shoe rubbing on a prominent joint; classic with hammertoe deformity.
6
Heel fissure rimVertical cracks in the heel callus margin; risk of cellulitis if deep.
Conservative Nursing Management
For most patients, conservative management is highly effective when paired with addressing the underlying pressure source.
✓ Do
Pare or file calluses gradually with a pumice or foot file after softening (warm water, not soaking)
Apply urea- or lactic-acid-based emollients to thickened areas and heel fissures daily
Identify and address the pressure source: footwear fit, hammertoe deformity, gait abnormality
Recommend silicone toe sleeves, donut pads, or interdigital separators for corns
Refer to podiatry for sharp debridement of thick calluses, recurrent corns, or persistent fissures
Consider orthotic referral when biomechanical factors drive recurrence
✕ Don't
Use razors or blades for self-debridement (patient or staff outside scope and credentialing)
Apply over-the-counter salicylic acid corn pads in patients with diabetes, peripheral artery disease, or neuropathy
Soak feet for prolonged periods — softens healthy skin and worsens fissures
Pare aggressively in a single session — repeated gentle reduction is safer
Treat the lesion without identifying the underlying pressure source
Ignore a callus in a patient with diabetes — it is a marker of pressure that may evolve to ulceration
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Critical Safety Alert: Salicylic Acid & Diabetes
Over-the-counter corn and callus removers containing salicylic acid are contraindicated in patients with diabetes, peripheral artery disease, or peripheral neuropathy. The acid causes chemical injury that can extend through insensate skin and create a non-healing wound. Always ask about these products when assessing a foot wound — patients often don't volunteer it.
The Diabetic Callus: Why It Matters More
A callus on a healthy foot is a nuisance. A callus on a foot with diabetic neuropathy is a pre-ulcer.
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The IWGDF principle
In patients with loss of protective sensation, plantar calluses indicate elevated focal pressure that the patient cannot feel. Without intervention, the tissue beneath the callus can break down silently into a sub-callus ulcer. International Working Group on the Diabetic Foot guidance recommends regular professional callus reduction in this population — not patient self-care.
For a patient with diabetes presenting with a new or growing plantar callus, the appropriate nursing actions are:
1. Document location, size, and any surrounding erythema, warmth, or fluid.
2. Inspect carefully for any sub-callus ulceration after gentle paring or with provider assistance.
3. Confirm sensation status and foot risk category (loss of protective sensation = elevated risk).
4. Refer to podiatry or wound care for professional debridement and offloading review.
5. Reinforce daily foot inspection and absolute avoidance of self-treatment with razors or salicylic acid.
Red Flags: When to Refer
⚠️ Escalate beyond routine nursing care when…
Pain disproportionate to the visible lesion
Erythema, warmth, or fluctuance surrounding a callus or corn
Drainage, foul odor, or any sign of infection
Patient with diabetes presents with a new, growing, or changing callus
Heel fissure with bleeding, deep cracking, or signs of cellulitis
Failure to improve after several weeks of appropriate conservative management
Recurrent corns despite footwear modification — possible underlying bony deformity needing imaging or surgical consultation
Patient Education & Prevention
Patient Teaching
Six habits that prevent recurrence
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Properly fitting shoes
Width matters as much as length
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Daily moisturization
Urea-based for heels and dry skin
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Pumice gradually
Light, regular use after bathing
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No bathroom surgery
Never razors, blades, or knives
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No medicated corn pads
In diabetes, PAD, or neuropathy
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Daily inspection
Watch for redness or new pain
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Patient Teaching Moment
A 66-year-old patient with type 2 diabetes mentions a callus on the ball of her foot has been growing for "a few months." She's been using a salicylic acid corn pad on it. The nurse documents the callus location and size, removes the pad, inspects carefully for any sub-callus breakdown, confirms protective sensation status, and refers to podiatry for professional debridement and offloading review — all while gently educating the patient on why salicylic acid is unsafe given her diabetes. Two corrections in one visit, no judgment.
Ready to check your understanding? Take the quick knowledge check for this lesson.
Educational Disclaimer
The information on this website and any communication with RNscrub Foot Care is provided for educational and informational purposes only. It is not a substitute for medical advice, diagnosis, or treatment. Patients are always encouraged to consult with their primary care provider or appropriate specialist for individual clinical decisions.
References
International Working Group on the Diabetic Foot (IWGDF). IWGDF Guidelines on the Prevention and Management of Diabetes-Related Foot Disease. 2023.
Bus SA, Lavery LA, Monteiro-Soares M, et al. Guidelines on the prevention of foot ulcers in persons with diabetes (IWGDF 2023 update). Diabetes/Metabolism Research and Reviews. 2024;40(3):e3651.
