A callus is a thickened, hardened area of skin that forms on the foot, often appearing on the heel or sole as a yellowish or pale plaque. The formation of this tougher skin layer, known medically as hyperkeratosis, is a protective biological response. It occurs when skin is subjected to persistent, localized friction, pressure, or irritation, serving to shield the underlying tissues from damage. While minor calluses can be harmless, excessive thickening can cause discomfort and signal an underlying issue. This article explores the primary reasons why these protective skin formations occur specifically on the heel.
Footwear and External Pressure
The most common external factor contributing to heel calluses is the interaction between the foot and its covering, or the surface it rests on. Ill-fitting footwear, whether too tight or too loose, is a frequent cause of abnormal friction and shearing force against the heel. When a shoe is too loose, the heel slides back and forth against the shoe material, generating repeated rubbing that triggers the skin’s defense mechanism to thicken.
Specific types of shoes can create predictable points of pressure or friction that lead to callus formation. High heels shift the body’s weight distribution, altering the mechanics of the heel strike, which can contribute to friction-related calluses. Open-backed shoes, such as sandals and slippers, force the foot to grip or slide, causing the heel pad to expand and contract unnaturally upon impact, leading to excessive rubbing on the edges of the heel.
Prolonged standing on hard, unforgiving surfaces, like concrete floors, increases the static pressure exerted on the heel, compressing the skin against the bone. This sustained force prompts the skin cells to rapidly accumulate as a protective barrier against the constant compression. Even in well-fitting shoes, high-impact activities like running or walking for extended periods cause repetitive stress that results in callus formation, as the skin attempts to protect itself.
Structural Foot Mechanics
Structural foot mechanics refer to the internal biomechanical issues that dictate how the heel strikes the ground and bears weight. Abnormalities in the gait cycle, or walking pattern, are a significant cause because they lead to uneven distribution of force on the heel. Instead of the weight being absorbed and dispersed evenly across the foot, it becomes concentrated on a small, specific area.
Foot structure variations greatly influence where pressure is focused. Flat feet, or excessive pronation, cause the foot to roll inward during walking, leading to increased pressure and callus formation on the inner edge of the heel. Conversely, a foot with a high arch (underpronation or supination) has less surface area contact with the ground, concentrating the weight-bearing force on the outer heel and ball of the foot.
Structural deformities, such as a heel spur or other bony prominences, can intensify pressure on a localized area, since the skin is compressed between the hard surface and the protruding bone. Additionally, the natural fat pad beneath the heel can thin out or shift with age, reducing the body’s innate cushioning. When this happens, the skin responds with a higher rate of cell production to replace the lost natural padding.
Extreme Skin Dryness
Extreme skin dryness, medically termed xerosis, is a dermatological condition that significantly contributes to the severity of heel calluses. While pressure and friction are the initial triggers for callus development, severely dry skin is less pliable and more prone to hardening. This lack of moisture causes the skin to lose its natural elasticity and flexibility, making it brittle under stress.
When the thickened, dry skin of the heel is subjected to the normal forces of walking, it cannot stretch and accommodate the expansion of the heel pad upon impact. Instead, the hardened skin begins to crack and fissure, a common issue known as cracked heels, which is an advanced stage of callus formation.
Natural aging also plays a role as the skin’s ability to retain moisture declines, leading to a drier surface that is more susceptible to rapid thickening when pressure is applied. Environmental factors, such as low humidity in the air, further exacerbate the problem by drawing moisture out of the skin.