Friction and Pressure Lesions

A friction blister forms when repeated shear separates layers within the epidermis and the space fills with fluid. Moisture increases the friction between skin and sock or equipment, so sweaty feet and new or poorly fitted footwear are common triggers. Blisters typically affect the heels, toes and balls of the feet in runners and court-sport players, and the palms and fingers in racquet, rowing and gymnastic sports.

Management depends on the blister. A small, intact and comfortable blister is best left alone, since the intact roof is a natural sterile dressing that protects the raw skin beneath. A large, tense or painful blister can be drained: clean the skin, pierce the edge with a sterile needle, express the fluid, and leave the roof in place rather than removing it, then cover with a clean dressing or a hydrocolloid. The roof should only be removed if it is already torn or the blister is infected. If a blister becomes infected, trim only loose or non-viable roof, use local wound care, and reserve an oral antibiotic for when there is spreading cellulitis, guided by local antimicrobial advice.

Persistent pressure and friction lead the skin to thicken protectively, producing a callus or a corn. A callus is a broad area of thickened skin, often over the ball of the foot or the palm, whereas a corn is a smaller, focal area of hard skin with a central core, typically over a bony prominence. A hard corn usually sits over a toe joint, while a soft, macerated corn forms between the toes where moisture is trapped. Both are usually a response to a mechanical problem rather than a disease in themselves.

Management combines reducing the thickened skin with correcting the cause. The hard skin can be pared or filed down, and softened with an emollient containing urea or salicylic acid. Offloading the pressure with padding, and correcting the underlying mechanics through better-fitting footwear or an orthosis, treats the reason the lesion formed and reduces recurrence. Paring should be cautious and not too deep. A person with diabetes, neuropathy or impaired circulation should not self-pare or use keratolytic acids, since a break in the skin risks ulceration and infection; they need a foot-risk assessment and podiatry or diabetic-foot input.

Several other friction lesions are worth recognising. Chafing is friction between skin surfaces or between skin and clothing, commonly affecting the inner thighs, groin and axillae, and it is worsened by moisture and by coarse or wet fabric. Jogger's nipple is soreness and sometimes bleeding of the nipple from repeated rubbing against a running vest, seen particularly in distance runners. Black heel, also called talon noir, is a black or dark area on the heel caused by tiny shear haemorrhages within the skin, common in court and jumping sports; it is harmless, but its dark colour can mimic a melanoma, and gently paring the surface removes the superficial blood, which supports the diagnosis of talon noir, though persistent, changing or uncertain pigmentation still needs dermoscopy or specialist assessment to exclude a melanoma. Piezogenic pedal papules are small bumps on the side of the heel that appear on standing, caused by fat pushing through the skin's supporting tissue, and are usually painless and benign.

The common thread is to distinguish a benign friction lesion from something that needs further thought, and to reassure and manage accordingly.

Prevention is the most valuable part of managing friction and pressure lesions, because the same forces will keep producing them until the cause is addressed.

Footwear should fit well and be broken in gradually rather than worn hard for the first time on competition day. Moisture-wicking synthetic or acrylic socks worn without wrinkles keep the skin drier and reduce friction better than cotton, and changing damp socks helps on long efforts. Lubricants such as petroleum jelly reduce friction at known hotspots, and an antiperspirant containing aluminium chloride applied to the feet can reduce the sweating that drives blistering. Taping vulnerable areas, using blister plasters, and covering the nipples with tape or a barrier before long runs all help. Calluses and corns are prevented by redistributing pressure through padding, insoles or orthoses and by addressing the biomechanics that concentrate load. Attending to a hotspot early, before it becomes a blister, is far easier than treating the established lesion.

• •Friction blisters form when shear separates layers of the epidermis; moisture increases friction.
• •Leave a small intact blister; drain a large or painful one aseptically and keep the roof on.
• •Calluses and corns are pressure responses; treat the skin and correct footwear or mechanics.
• •Black heel is a benign shear haemorrhage that can mimic melanoma; paring reveals blood.
• •Pare hard skin with caution in people with diabetes or peripheral vascular disease.
• •Prevention with footwear, moisture-wicking socks, lubricants and taping is central.