Corns and Calluses

A callus is diffuse, poorly demarcated hyperkeratotic thickening of the stratum corneum that develops wherever skin is subjected to repeated low-grade friction or pressure — a genuinely protective adaptation, usually painless, and usually the same colour as the surrounding skin. A corn (clavus) is a more focal, sharply circumscribed hyperkeratotic lesion with a compacted keratin core that presses into the dermis; because that core sits directly over sensory nerve endings, corns are frequently painful, especially with direct perpendicular pressure.^[1] Corns are further split into 2 clinically distinct patterns: the hard corn (heloma durum), the most common type, which forms over a bony prominence — classically the dorsolateral fifth toe or an interphalangeal joint — and the soft corn (heloma molle), which forms between adjacent toes (most often the fourth web space) where trapped moisture keeps the compressed skin macerated and white rather than hard.^[1] Foot involvement from corns and calluses is common, reported in roughly 14-48% of the population depending on the series, with a female predominance linked to narrow, tapered footwear and rising prevalence with age as the protective plantar fat pad thins.^[1]

This is a genuine, guideline-endorsed self-care condition for most patients: correcting the footwear or biomechanical driver, offloading the pressure point with padding, and mechanically reducing the thickened skin resolve the great majority of cases without a prescription.^[2] The pharmacist's single highest-value contribution in this chapter is not choosing a keratolytic — it is recognizing, before recommending anything, whether the patient in front of them has diabetes, peripheral neuropathy, or peripheral arterial disease, since self-treatment and self-debridement carry a real ulceration and infection risk in that population and change the plan entirely (see Red Flags/Refer).^[1]

A less common pattern, the seed corn, presents as multiple small, painless keratotic plugs scattered within a plantar callus in a non-weight-bearing area and is generally an incidental finding rather than a symptomatic complaint.^[1]

Multiple corns on both feet, in a patient with pronounced transverse flat feet — this same photograph also shows a coexisting thick plantar wart on the right sole, illustrating why the 2 are easy to confuse at a glance. (Marionette, CC BY-SA 3.0 / GFDL, Wikimedia Commons)

Diffuse calluses — plantar on the right foot, medial on the left foot — showing the flatter, poorly demarcated, coreless thickening that distinguishes a callus from a corn. (Jmarchn, CC BY-SA 3.0, Wikimedia Commons)

Distinguishing a corn or callus from a plantar wart — a genuinely useful bedside test

Corns, calluses, and plantar warts can look similar at a glance, but 2 simple bedside findings reliably separate them once the overlying hyperkeratotic surface is gently pared:

^[1] Confirming this distinction matters clinically: a lesion treated as a corn that is actually a wart (or vice versa) will not respond as expected, and a wart specifically needs a management approach that a corn does not.

• Ill-fitting footwear — a toe box that is too narrow or too short, or a shoe that lets the foot slide and rub with every step — is the most common and most correctable driver.^[4][2]
• High heels, which shift and concentrate weight-bearing pressure onto the forefoot and metatarsal heads.
• Foot deformities that create new or exaggerated bony prominences and altered pressure points, including bunions (hallux valgus), hammertoes and claw toes, and other biomechanical gait abnormalities.^[4]
• Advancing age, through atrophy of the protective subcutaneous fat pad on the sole and forward displacement of the metatarsal heads.^[1]
• Female sex — a higher reported prevalence, largely attributed to narrow, tapered, or pointed-toe footwear styles.^[1]
• Obesity and excess body weight, which increase plantar pressure with every step.^[1]
• Repetitive athletic activity or occupations involving prolonged standing, walking, or running.^[1]
• A hereditary keratotic disorder in a patient with corns in atypical, non-weight-bearing locations (seed corns) — consider this when the distribution does not fit a simple friction/pressure pattern.^[1]

History

• Ask specifically about footwear (fit, heel height, how long the current pair has been worn) and about occupational or athletic activities involving prolonged standing, walking, or running.
• Screen for diabetes, peripheral neuropathy, and peripheral arterial disease before recommending any self-care product — this determines the entire management pathway (see Red Flags/Refer).
• Ask about pain characteristics: direct perpendicular pressure reproducing the pain points toward a corn; lateral squeezing reproducing the pain points toward a plantar wart.^[1]
• Ask about prior self-treatment — which product, how it was applied, and for how long — since incorrect technique (applying acid to normal surrounding skin, or stopping before the full course) is a common cause of an apparent "treatment failure."

Examination

Confirm the lesion's location and morphology against the patterns in Recognize the Condition — a diffuse, poorly demarcated, coreless area of thickening supports a callus; a small, sharply circumscribed lesion with a central core supports a corn; note whether it is over a bony prominence (hard corn) or macerated within a web space (soft corn). Gently paring the surface (or asking a colleague/prescriber to do so where scope permits) and checking for preserved skin lines and the absence of black thrombosed-capillary dots supports a corn or callus over a plantar wart.^[1]

Differential diagnosis

^[1]

Investigations

Most corns and calluses are diagnosed on history and inspection alone; no laboratory testing or imaging is routinely needed. Dermoscopy can help confirm the diagnosis when uncertainty remains after the bedside pare-test.^[1] Weight-bearing radiographs are reasonable when a significant underlying bony deformity (a prominent metatarsal head, a severe hammertoe, or advanced hallux valgus) is suspected as the driver and surgical correction is being considered.^[1] If diabetes has not already been established or ruled out in a patient presenting with recurrent or atypical corns/calluses, a fasting glucose is a reasonable screen, since this red-flag population overlaps directly with the group who should not self-treat.^[1]

• Identify and correct the underlying friction or pressure source — footwear, gait, or a structural deformity — since treating the lesion without addressing its cause invites prompt recurrence.
• Reduce the hyperkeratotic tissue safely to relieve pain and pressure.
• Screen every patient before recommending self-care, and route diabetes, peripheral neuropathy, and peripheral arterial disease patients to professional assessment rather than OTC keratolytics or self-debridement.
• Prevent complications — maceration, fissuring, secondary bacterial infection, and, in at-risk patients, ulceration.
• Set realistic expectations: most corns and calluses recur if the underlying friction/pressure source is not corrected, regardless of how effectively the lesion itself is treated.
• Recognize and refer promptly when self-care fails, when the diagnosis is uncertain, or when signs of infection or skin breakdown develop.

• Footwear correction is the single most important non-pharmacologic measure. Choose shoes with a toe box wide and deep enough that toes are not squeezed or overlapped, and a heel low enough to avoid concentrating pressure on the forefoot; a useful practical check is roughly a finger's width (about 1.25 cm) of space between the longest toe and the front of the shoe.^[2]
• Protective padding offloads pressure directly from the lesion: a soft pad with a hole cut to fit around a corn, moleskin over the sore area, a latex foam or gel insole, or a silicone toe sleeve/interdigital spacer for a soft corn between the toes.^[2]
• Mechanical debridement with a pumice stone, callus file, or emery board — soak the foot for 5-10 minutes first, then gently work a pumice stone over wet skin (or a file/emery board over dry skin) to reduce the thickened tissue; repeat roughly weekly rather than daily, and stop with any sign of irritation or bleeding.^[2][1]
• Never cut a corn or callus with a razor blade, knife, or scissors at home — this is genuinely dangerous and a recognized cause of infection, and is specifically discouraged in patient-facing guidance for exactly this reason.^[2]
• Where a specific biomechanical driver is identified (a bunion, a hammertoe, or an abnormal gait pattern), an orthotic or referral for biomechanical assessment addresses the root cause rather than only the resulting lesion.^[4]
• Keep the feet clean and dry, and change socks daily, particularly if managing a soft corn prone to maceration between the toes.

Diabetes, peripheral neuropathy, and peripheral arterial disease

Pregnancy

Corns and calluses are managed the same way in pregnancy, with an emphasis on the non-pharmacologic measures (footwear, padding, gentle mechanical debridement) as first-line given the very limited systemic-exposure data for topical salicylic acid used over a small area in pregnancy; if pharmacologic treatment is genuinely needed, use the smallest effective area and duration and involve the prescriber or pharmacist in that specific decision rather than defaulting to it.

Breastfeeding

Topical salicylic acid applied to a small skin area carries minimal systemic absorption and is not expected to be a concern in breastfeeding; non-pharmacologic measures remain first-line regardless.

Pediatrics

Favour non-pharmacologic management (correct-fitting footwear as the child's foot grows, padding, gentle debridement) as first-line. If a keratolytic is genuinely needed, use it under caregiver supervision with careful attention to surrounding-skin protection and duration — young children are at higher risk of salicylate toxicity with excessive or prolonged topical salicylic acid exposure relative to their body size, so avoid large treatment areas or prolonged unsupervised use.

Older adults

Age-related atrophy of the protective plantar fat pad and a higher prevalence of foot deformities make calluses and corns more common and more likely to recur in this group.^[1] Screen carefully for diabetes, neuropathy, and circulatory compromise before recommending self-care, since these conditions are also more prevalent with advancing age, and consider a lower threshold for podiatry referral given higher fall risk when a painful plantar lesion affects gait.

Immunocompromised patients

Apply the same caution as for diabetes/PAD — impaired wound healing and a higher infection risk argue against self-debridement or keratolytic self-treatment; involve a prescriber or podiatrist for anything beyond footwear and padding advice.

For patients using topical salicylic acid, reassess at the end of the planned course (up to 14 days) — confirm the lesion has softened and reduced in size, and check specifically for irritation or damage to the surrounding normal skin, which suggests the protective barrier technique needs to be revisited rather than that the product has failed.^[3]

1. Confirm the diagnosis is genuinely a corn or callus and not a plantar wart or another mimic (see Assessment/Diagnosis) — a lesion that does not respond as expected may simply be the wrong diagnosis.
2. Confirm the underlying friction/pressure source was actually corrected — new or better-fitting footwear, padding in place, and any biomechanical driver addressed — since an uncorrected cause will keep reproducing the lesion regardless of which product is used.
3. Confirm correct application technique for salicylic acid: soaking first, application limited to the lesion itself, and surrounding-skin protection, rather than assuming the product itself is ineffective.
4. Re-screen for diabetes, peripheral neuropathy, and peripheral arterial disease if this was not already established — a red flag missed at the first visit is a common reason self-care appears to be failing or, worse, is actively causing harm.
5. If diagnosis, technique, and footwear correction are all confirmed adequate but the lesion persists or recurs, refer for professional debridement and biomechanical assessment — a persistent hard corn over a hammertoe or a recurrent soft corn in a tight web space may need definitive correction of the underlying deformity.
6. Any sign of infection, ulceration, or skin breakdown at any point: stop self-care and refer promptly rather than continuing or switching OTC products.

• Recommending a salicylic acid keratolytic or self-debridement to a patient with diabetes, peripheral neuropathy, or peripheral arterial disease without screening for these conditions first — this is the single most consequential error in this chapter.
• Applying salicylic acid to the entire foot or a wide area around the lesion rather than protecting normal surrounding skin — salicylic acid does not distinguish dead from living tissue.
• Treating a plantar wart as a corn (or vice versa) without checking skin-line continuity and the presence or absence of black thrombosed-capillary dots after gentle paring.
• Recommending a keratolytic or pumice stone without addressing the footwear or biomechanical cause — the lesion will simply recur.
• Using a razor blade, knife, or scissors for home debridement, or endorsing a patient's request to do so.
• Using liquid nitrogen (cryotherapy) on a corn or callus — it damages surrounding normal skin without treating the underlying lesion.
• Continuing the same self-care regimen past 14 days without reassessment, rather than escalating to professional debridement when an adequate trial has not worked.
• Missing a hereditary keratotic disorder in a patient with corns in atypical, non-weight-bearing locations rather than the usual friction points.

How to use this table: Doses are adult doses and require patient-specific confirmation. Screen for diabetes, peripheral neuropathy, and peripheral arterial disease before recommending any product in this table — see Red Flags/Refer. Select any drug name to open its complete Pharmasist Drug Database page.

Topical Keratolytics

Reserve for patients without diabetes, peripheral neuropathy, or peripheral arterial disease. Always soak and dry the foot first, and protect surrounding normal skin from acid contact.

Skin-Barrier Adjunct

Not a treatment for the lesion itself — protects healthy surrounding skin during salicylic acid therapy.