Running Blisters: Causes, Prevention, and Management of Inner Heel Blisters

Why Do I Get Blisters on the Inside of My Heel When I Run?

Blisters on the inside of the heel during running are primarily caused by repetitive friction and shear forces acting on the skin, often exacerbated by ill-fitting footwear, inappropriate socks, excessive moisture, or specific biomechanical factors related to your gait.

Understanding Blister Formation

A blister is a small pocket of fluid (serum, plasma, blood, or pus) that forms in the upper layers of the skin, typically as a result of forceful rubbing or trauma. In the context of running, this trauma manifests as repetitive shear forces. As your foot moves within your shoe, particularly during the push-off and landing phases, the skin on your heel can stretch, compress, and rub against the shoe's heel counter or sock. When these forces exceed the skin's elasticity and strength, the layers of the epidermis separate, and fluid fills the void, forming a blister. The inside of the heel is particularly susceptible due to its anatomical prominence and the dynamic movements of the foot during the gait cycle.

Primary Causes of Inner Heel Blisters in Runners

Several factors, often in combination, contribute to the formation of blisters on the inside of the heel:

• Improper Footwear Fit:

  • Shoes Too Large: If your running shoes are too big, your foot can slide forward and backward excessively, causing the heel to rub against the heel counter.
  • Shoes Too Small/Narrow: While less common for inner heel blisters, a shoe that is too tight can create pressure points and restrict natural foot expansion, increasing friction.
  • Inadequate Heel Lock: A shoe that doesn't adequately secure the heel can lead to slippage. The heel counter, the stiff part at the back of the shoe, might not be shaped correctly for your foot, or the lacing system might not provide sufficient lockdown.
  • Worn-Out Shoes: The internal lining of older shoes can degrade, becoming rough or uneven, increasing friction.

• Inappropriate Socks:

  • Cotton Socks: Cotton absorbs moisture (sweat) and holds it against the skin, increasing friction. Wet skin is more pliable and susceptible to blistering. Cotton also tends to bunch up, creating hot spots.
  • Poorly Fitting Socks: Socks that are too loose can wrinkle and bunch, creating friction points. Socks that are too tight can restrict blood flow and apply constant pressure.
  • Prominent Seams: Seams in socks, particularly around the heel area, can rub against the skin, initiating blister formation.

• Biomechanical Factors:

  • Excessive Heel Slippage: This is often a direct result of improper shoe fit or lacing but can also be influenced by the runner's gait.
  • Overpronation: While more commonly associated with medial arch issues, excessive inward rolling of the foot (overpronation) can alter how the heel interacts with the shoe, potentially increasing shear forces on the inner heel.
  • Foot Strike Mechanics: A heavy heel strike or an inefficient push-off can increase the forces exerted on the heel against the shoe.
  • New Running Form/Shoes: Changes in your running technique or transitioning to a different shoe type can alter pressure distribution, leading to new friction points.

• Environmental Conditions:

  • Heat and Humidity: Increased sweat production raises moisture levels, softening the skin and making it more prone to friction.
  • Wet Conditions: Rain, puddles, or even high humidity can saturate socks and shoes, drastically increasing friction.

• Individual Anatomical Factors:

  • Prominent Heel Bone (Calcaneus): Some individuals may have a heel shape that protrudes more, making it inherently more susceptible to rubbing within a standard shoe.
  • Foot Swelling: Natural foot swelling during prolonged exercise can cause shoes to feel tighter, increasing pressure and friction.

Comprehensive Strategies for Prevention

Preventing inner heel blisters requires a multi-faceted approach focusing on proper equipment and foot care.

• Footwear Optimization:

  • Proper Fit is Paramount: Get professionally fitted at a specialized running store. Ensure there's a thumb's width of space between your longest toe and the end of the shoe. Crucially, your heel should feel secure without excessive movement.
  • Try Shoes Later in the Day: Your feet swell throughout the day, so trying on shoes in the afternoon or evening can help ensure a comfortable fit when your feet are at their largest.
  • Test Run: If possible, take the shoes for a short run on a treadmill or around the store to assess heel slippage.
  • Consider Heel Counters: Some shoes have softer or more rigid heel counters. Experiment to find what works best for your foot shape.

• Socks Selection:

  • Moisture-Wicking Materials: Opt for socks made from synthetic blends (e.g., polyester, nylon, acrylic) or merino wool. These materials draw moisture away from the skin, keeping your feet drier.
  • Seamless Design: Choose socks with flat or no seams, especially around the heel, to eliminate potential friction points.
  • Proper Fit: Ensure socks fit snugly without being too tight or too loose, preventing bunching or sagging.
  • Double-Layer Socks: Some runners find relief with double-layer socks, where the inner layer moves with the foot and the outer layer moves with the shoe, effectively reducing friction on the skin.

• Lacing Techniques:

  • Heel Lock Lacing (Runner's Loop): This technique uses the top eyelets of your shoe to create a tighter, more secure fit around the ankle, significantly reducing heel slippage.
  • Experiment with Tension: Ensure laces are snug but not overly tight, which can cause pressure points.

• Foot Care and Preparation:

  • Antiperspirant/Powder: Applying an antiperspirant to your feet, particularly the heel area, can help reduce sweat and keep the skin drier. Absorbent powders can also be effective.
  • Friction-Reducing Balms: Products like anti-chafing sticks or balms create a protective barrier on the skin, reducing direct friction.
  • Taping: For known hot spots or during long runs, applying athletic tape (like Kinesiology tape or paper tape) directly to the skin before running can provide a durable, low-friction surface. Ensure the skin is clean and dry for optimal adhesion.
  • Callus Management: While calluses offer some protection, excessive, hard calluses can sometimes create rigid friction points. Keep them managed, but don't remove them entirely, as they do provide a natural barrier.

• Biomechanical Considerations:

  • Gait Analysis: If persistent blisters are an issue despite proper footwear and socks, consider a professional gait analysis. A specialist can identify subtle biomechanical inefficiencies that might be contributing to excessive heel movement.
  • Orthotics: Custom or over-the-counter orthotics can sometimes help stabilize the foot within the shoe, reducing pronation or supination that might lead to heel slippage.

• Gradual Adaptation:

  • Break-In New Shoes: Always break in new running shoes gradually on shorter runs before attempting long distances.
  • Increase Mileage Slowly: Avoid sudden increases in running volume or intensity, which can stress your feet in new ways.

Proper Blister Management

If a blister does form, proper care is crucial to prevent infection and allow healing:

• Small, Intact Blisters: Leave them intact. The skin acts as a natural sterile barrier. Protect them with a blister plaster or moleskin.
• Large, Painful Blisters: If a blister is very large, painful, or likely to pop on its own, it can be drained under sterile conditions. Clean the area, sterilize a needle, puncture the edge of the blister, gently press out the fluid, and then cover with a sterile dressing. Never tear off the skin roof.
• Monitor for Infection: Watch for signs of infection: increased redness, swelling, warmth, pus, or fever.

When to Seek Professional Help

Consult a healthcare professional, podiatrist, or sports medicine specialist if:

• Blisters are recurrent, severe, or interfere significantly with your running.
• You suspect an infection (pus, spreading redness, fever).
• You have underlying health conditions like diabetes or poor circulation, which can complicate blister healing.
• You've tried various prevention strategies without success, suggesting a deeper biomechanical or anatomical issue.

By understanding the interplay of footwear, foot mechanics, and environmental factors, runners can significantly reduce their risk of developing painful inner heel blisters and enjoy their runs more comfortably.