Athletes' feet in focus: how runners effectively prevent blisters, pressure spots and black nails

What lies behind it

The human foot consists of 26 bones, numerous joints, ligaments and muscles. During running, three to five times one's own body weight acts upon this complex structure. With every step, this biomechanical load is distributed across the heel zone, the lateral border of the foot, the ball of the foot and finally across the toes as the push-off zone. The epidermis of the plantar surface is equipped with a prominent stratum corneum to absorb mechanical forces.

Friction occurs when the running shoe or sock shears against the skin surface. During repetitive movements, the upper layer of the epidermis separates from the underlying dermis. Tissue fluid accumulates in the resulting cavity, leading to the formation of an epidermal blister. Blood vessels in the dermis can rupture under greater shear forces, causing the blister to fill with blood.

The phenomenon of the black nail, medically termed a subungual haematoma, arises from continuous microtrauma. With every step, the foot slides slightly forward in the shoe. The toe pads, particularly of the hallux or the second ray, repeatedly strike the toe box. This repetitive shock wave leads to the rupture of delicate capillaries in the nail bed. The extravasated blood collects between the nail bed and the rigid keratin plate of the nail. As the fluid cannot escape, focal pressure builds up, causing substantial pain and ultimately potentially leading to the detachment of the nail plate.

Typical signs

Runners usually notice shear-force damage to the foot as a circumscribed, burning sensation commonly referred to as a hotspot. If training continues at this site, a classic blister develops within a short time. This manifests as a tense fluid-filled vesicle that responds painfully to external pressure. If the deeper layers of the dermis are affected, the contents shimmer reddish to dark purple.

A subungual haematoma often only becomes noticeable after running. Those affected observe discoloration under the toenail ranging from bright red to a deep blackish purple. The affected toe typically throbs at rest. The pressure beneath the keratin plate intensifies when wearing closed footwear or during direct palpation. In the subsequent weeks, the haematoma gradually grows out with the nail, provided the nail bed has not been permanently damaged.

Symptomatically, these acute traumas must be distinguished from chronic fungal infections or malignant skin changes. Tinea pedis, classic athlete's foot, manifests primarily as erythema, scaling, interdigital maceration and intense pruritus. Onychomycosis is characterized by a brownish-yellow discoloration, thickening and crumbling of the nail plate without a preceding acute painful trauma. Particular attention is required for dark pigmentation under the nail that does not migrate forward with nail growth. This may represent a subungual melanoma, which requires immediate evaluation by a specialist physician.

Causes in everyday life

The primary cause of skin and nail problems in athletic feet is ill-fitting footwear. A running shoe that is too small reduces the necessary toe clearance. During downhill running, the toes strike the toe box unhindered. Conversely, if a running shoe is chosen too large, the heel loses its grip. The foot slides back and forth inside the shoe, generating extreme shear forces on the plantar surface.

Another underestimated factor is moisture management within the shoe. During intensive training, the sweat glands of the plantar sole produce significant amounts of moisture. Macerated skin swells, loses its natural barrier function and reacts extremely sensitively to friction. Cotton socks retain this moisture and considerably amplify frictional forces, whereas specialized technical fibres wick sweat secretions away to the exterior.

Biomechanical deformities of the musculoskeletal system alter pressure distribution on the plantar surface. A splay foot combined with flat arches leads to overload of the central metatarsal heads. Overpronation causes the foot to collapse inwards during the roll-over phase, exposing the medial border of the hallux to increased friction. Hammer toes or claw toes increase localized pressure on the dorsal aspects and tips of the toes.

Improper foot care also contributes to complaints. Toenails cut too short with filed corners encourage the nail to grow into the lateral nail fold. Excessively long nails, on the other hand, act like a lever inside the running shoe. Every impact transfers the leverage directly to the nail bed, tearing its attachment. Insufficient removal of excess callus also leads to issues, as thick hyperkeratotic plaques can split painfully under load.

When medical evaluation is necessary

Although many foot problems in sports are benign, clear warning signs exist that necessitate immediate medical evaluation. Prompt assessment is indispensable if a blister or the tissue surrounding a subungual haematoma becomes inflamed. Signs of a bacterial superinfection include increasing erythema, localized heat, throbbing pain, pus formation or red streaks spreading towards the lower leg.

Medical evaluation is also urgently recommended for:

• Individuals with existing diabetes mellitus, peripheral arterial disease or neuropathy.
• Sensory disturbances in the feet, as tissue damage can progress rapidly without pain perception.
• Patchy, brown-black discolorations beneath the nail that appeared without identifiable trauma or have failed to grow out for months.
• Complete detachment of the nail plate accompanied by an open, weeping nail bed injury.
• Severe, unbearable pressure pain caused by a fresh subungual haematoma within the first 24 to 48 hours.

In these cases, it must be ruled out that deeper tissue layers have sustained damage or that an underlying dermatological condition is present. General practitioners, dermatologists or orthopaedic specialists provide the primary medical diagnosis and initiate pharmacological or surgical treatment where appropriate.

What podiatric treatment can achieve

Professional podiatry serves as the interface between prevention, medicine and specialized foot care. In our practice, care begins with a comprehensive medical history and inspection of the skin and nail structure. The nail plate is thoroughly examined for microtrauma, discoloration and structural tension.

If a runner presents with a thickened or traumatized nail, podiatric nail management and treatment are utilized. Using modern rotary instruments and diamond burs, the thickened nail plate is thinned down painlessly. This immediately reduces pressure on the highly sensitive nail bed. Should the nail structure tend to curl due to repetitive trauma, an individualized orthonyxia nail brace treatment can be applied. The spring force of the brace gently lifts the nail edges from the nail fold, thereby preventing painful ingrowth.

In cases of nail plate substance loss, podiatric nail prosthetics offer an effective method for restoration. A medical-grade synthetic resin replaces the missing section of the nail. This protects the exposed nail bed from hyperkeratosis and guides the regrowing natural nail along its correct path.

Treatment of the skin includes the professional debridement of hyperkeratoses and corns that have formed due to abnormal loading during running. Using scalpel techniques or rotary burs, the podiatrist precisely removes excess callus without damaging the underlying healthy tissue. For pressure relief in toe deformities or persistent friction points, custom-made silicone orthoses are crafted. These orthoses fit precisely into the interdigital spaces and redistribute mechanical forces during running.

Regular professional foot care at intervals of four to six weeks ensures that athletic feet remain resilient even during intense training phases. Learn more about our range of services and individual areas of application on our services page.

What you can do yourself

To protect athletic feet from friction, blister formation and subungual haematomas, runners should establish a consistent preventive routine in their daily lives. Careful material selection and correct foot care techniques form the foundation for pain-free distance running.

The following measures effectively support foot health in running:

• Check running shoe fit: When standing, running shoes should offer a thumb's width of space in front of the toes, corresponding to approximately 10 to 15 millimetres. Because feet swell under load, running shoes should ideally be fitted in the afternoon or evening.
• Adjust lacing: Use heel lock or marathon lacing utilizing the extra eyelet of the running shoe. This secures the heel firmly in the shoe and prevents the foot from sliding forward during downhill running.
• Wear technical socks: Discard 100 percent cotton socks. Use double-layer running socks or socks made of synthetic technical fibres or merino blends, which rapidly wick moisture away and absorb friction between the layers.
• Apply skin protection: Apply specialized deer tallow cream, petroleum jelly or anti-blister sticks to known friction points on the heels, balls of the feet and toes before long runs.
• Correct nail length properly: Always trim toenails straight across and only lightly round the corners with an emery board. The nail plate should align flush with the tip of the toe to prevent growth disturbances.

In addition, regular care of the skin barrier is beneficial. Rich foam creams containing ingredients such as urea support skin elasticity without clogging pores. Footbaths should be avoided before long runs, as they soften the skin and render it more susceptible to shear forces.

Common mistakes

In podiatric practice, the same typical errors committed by runners out of ignorance recur frequently. The most serious mistake when a black nail appears is attempting to drill through or puncture the nail plate oneself using a red-hot paperclip or needle. This method carries a tremendous risk of infection. Through the opening, bacteria can penetrate deep into the nail bed and cause irreversible inflammation of the bone or nail matrix.

Another widespread misconception involves puncturing or cutting open blisters. Opening a blister with non-sterile tools destroys the skin's natural protective barrier. The resulting open wound quickly comes into contact with pathogens inside a sweaty running shoe. As a rule, blisters should be kept intact and covered with a hydrocolloid blister plaster. A hydrocolloid dressing provides a moist wound environment and protects against further pressure.

Incorrect nail trimming also routinely leads to protracted problems. Many athletes cut the sides of the nails deeply, intending to relieve pressure in the shoe. However, this causes the regrowing nail to pierce sharply into the lateral nail fold. The consequence is painful granulation tissue and purulent inflammation.

Finally, many runners rely exclusively on thick cushioning systems in the shoe while neglecting sock selection. A high-quality cushioned shoe loses its efficacy if moist cotton socks macerate the skin and leave it unprotected against friction.

Current evidence and medical perspective

Scientific research in sports dermatology and podiatry highlights the significant relevance of biomechanical and material factors for foot health in endurance athletes.

Studies on marathon runners demonstrate that skin-related lesions are among the most frequent medical complaints during and after competitions [1]. Shear forces generated by repetitive ground impact produce thermal and mechanical stresses within the superficial skin layers [2].

Studies on blister prevention demonstrate the superiority of double-layer sock systems and synthetic fibres over conventional cotton [3]. Moisture exposure does not reduce the coefficient of friction of the skin, but rather increases adhesion between textile and epidermis, accelerating blister formation.

Regarding subungual haematoma, biomechanical analyses indicate that impact loading on the toe tip increases exponentially when toe box volume inside the shoe is inadequate [4]. An appropriate fit significantly reduces the risk of microtrauma to the nail bed. Clinical data collections demonstrate that podiatric interventions, such as the painless debridement of hyperkeratoses and the application of custom pressure relief devices, lead to a noticeable reduction in peak pain during exertion [5].

Treatment in Memmingen

For athletes from the Memmingen region, Unterallgäu and Upper Swabia, FREITAG® Podologie GmbH offers a professional point of contact for all questions regarding stress-related foot problems. The practice is managed by Helga Maria Freitag, who has been practicing as a state-recognized podiatrist since July 2025 and as a sectoral practitioner for podiatry (sektorale Heilpraktikerin für Podologie) since March 2026.

In the modern premises at Kempterstr. 25 in Memmingen, athletic feet are treated using modern methods and under the strictest hygiene standards. In addition to classic podologische Komplexbehandlung (comprehensive podiatric treatment), the portfolio includes custom orthoses, orthonyxia nail brace treatment and innovative cold therapy. Appointments can be made directly to optimally prepare feet for the upcoming running season. Simply get in touch via our contact page.

Acute care and recovery after competitions

Following prolonged endurance events such as a marathon or ultra-trail through the Allgäu Alpine Foothills, overworked feet require structured recovery. In the first two to four hours after crossing the finish line, pain and oedema reduction take priority. Elevating the lower legs supports venous return, reducing intravascular pressure within the fine capillaries of the plantar surface.

Applying cold for a maximum of ten to fifteen minutes constricts blood vessels and limits inflammatory tissue reactions. Ice packs must never be applied directly to bare skin, as this carries a risk of tissue damage from frostbite. Lukewarm or cool partial foot baths without soapy additives gently cleanse the skin of sweat salts. Hot foot baths should be avoided immediately after physical exertion: the heat increases blood flow and exacerbates fluid extravasation into pre-existing blisters.

A typical clinical case illustrates the correct approach: a 42-year-old runner experienced a painful pressure sensation beneath the second toenail following a 30-kilometre run. Rather than drilling through the nail, he cooled the toe, elevated the foot and applied a sterile dressing. Within 48 hours, the peak acute pain subsided. Over the following months, the small haematoma migrated forward painlessly with nail growth. Epidermal regeneration of micro-lesions typically takes seven to fourteen days. During this period, training volume should be significantly reduced to allow tissue healing.

Special considerations in trail running and downhill running

Running on uneven terrain presents completely different biomechanical demands compared to running on flat asphalt. During downhill running, substantial braking forces act upon the forefoot. With every step, the foot is pressed forward against the toe of the shoe. This increases the shear forces on the nail bed of the hallux and second ray exponentially.

Furthermore, continuous pronation and supination movements on root-strewn paths result in increased lateral friction along the malleoli and the outer borders of the foot. Waterproof membranes made of PTFE or similar synthetic materials pose an additional problem. While keeping external moisture out, they simultaneously hinder the optimal evaporation of foot sweat in mild temperatures. Skin swells more rapidly in the warm, humid environment inside the shoe, drastically reducing the mechanical resilience of the epidermis.

Under dry conditions, trail runners should choose highly breathable mesh materials and utilize gaiters. Gaiters prevent small pebbles and sand grains from entering the shoe. Even a single grain of quartz sand acts like sandpaper under heel pressure and can produce deep blisters within just a few kilometres. Runners in the Upper Swabian Hills or the Unterallgäu should readjust their lacing system before long downhill sections. Targeted fixation of the midfoot effectively prevents the foot from sliding forward.

Functional taping and relief dressings

Functional taping has become an established method for targeted prevention of friction and pressure damage. Unlike applications for muscular complaints, skin protection focuses on mechanical barrier function. Inelastic zinc oxide tape protects vulnerable skin areas on the heel or toe pads from direct shear forces.

Application requires precision and complete freedom from creases. Even the smallest wrinkle in the tape creates a new pressure point under body weight, rapidly leading to tissue damage. Prior to application, the skin must be thoroughly cleansed, degreased and completely dried. A skin barrier spray can be applied as a protective, adhesive-enhancing intermediate layer. For excessively sweaty feet, elastic kinesiology tape secures vulnerable zones, as its acrylic adhesive offers greater resistance to moisture.

To relieve pressure from deformities such as a mild claw toe, small, custom-cut felt or foam pads can be anchored beneath the tape. These pads redistribute pressure from the sensitive toe pad to biomechanically more resilient areas of the foot. After exercise, the tape must be removed slowly and parallel to the skin in the direction of hair growth. Abrupt ripping damages the epidermal tissue and negates the protective effect of the intervention.