What is a callus?

What is a Callus?

A callus (also called hyperkeratosis) is a hard, thickened area of skin that develops as a protective response to chronic friction or pressure, appearing as yellowish or whitish patches typically on weight-bearing surfaces like the soles of feet, tips of toes, or underneath metatarsal heads. 1, 2

Definition and Pathophysiology

• Calluses result from hyperkeratosis—excessive accumulation of keratin in the stratum corneum—representing a normal physiologic response of keratinocytes to repetitive mechanical stress 1, 3
• The thickening occurs as a direct hyperproliferative response where keratinocytes multiply in response to continuing friction or pressure 1, 2
• Unlike corns, calluses appear as diffuse thickened areas without a central core and are generally less painful 2, 4

Clinical Appearance

• Calluses present as hard, thickened, yellowish or whitish areas at pressure points with preserved skin lines (unlike warts, which disrupt skin lines) 2, 5
• They may become red if inflamed, causing confusion with other conditions 1, 5
• When located on weight-bearing surfaces, calluses can cause significant pain and difficulty walking if left untreated 2

Key Distinguishing Features from Similar Lesions

Callus vs. Corn

• Corns (heloma durum) have a hard, yellow appearance with a central nucleus or plug of keratin that extends downward in a cone-shaped point, causing pain described as "walking on a small stone or pebble" 1, 2
• Calluses lack this central core and are more diffuse 2, 4

Callus vs. Wart

• Paring down a wart exposes pinpoint bleeding from capillary loops, which is pathognomonic for verruca vulgaris 5
• Calluses maintain preserved skin lines, while warts disrupt them 5
• This distinction is critical because treatment approaches differ fundamentally 5

Treatment Approach

First-Line Conservative Management

• Professional blade or scalpel debridement by a podiatrist is the primary treatment, effectively removing thickened keratin 1, 2
• Self-management with emery boards or nail files after soaking in warm water can maintain results between professional treatments 1, 2, 6

Topical Therapy

• Urea-based creams (10-40%) applied daily to weekly reduce keratin thickness through keratolysis 1, 2, 7
• The FDA approves urea specifically for hyperkeratotic conditions including calluses, with superior safety compared to salicylic acid 6, 7

Prevention

• Pressure redistribution through proper footwear or padding prevents callus reformation 1, 2
• Addressing underlying mechanical causes (foot deformities, poorly fitting shoes) is essential for long-term resolution 3

Critical Clinical Pitfalls

• Never use chemical corn removers or plasters on diabetic patients due to high complication risk 5
• Avoid overdebridement, which makes underlying skin susceptible to blistering and tenderness, particularly in fragile skin conditions 6
• In diabetic patients, calluses require regular professional foot care due to increased risk of ulceration beneath hyperkeratotic tissue 1
• Biopsy suspicious lesions before aggressive debridement to exclude malignancy (squamous cell carcinoma can mimic hyperkeratosis) 2

When to Escalate Care

• Seek urgent evaluation if open ulceration develops, particularly in diabetic patients 2
• Refer for specialist care if painful fissures or cracks develop under the thickened tissue 1, 2
• Consider biopsy if lesions fail to respond to physical therapy, as this may indicate alternative diagnosis 2