Skin Findings in Runners: More Than Just Black and Blue Toes

Running offers athletes countless benefits, including weight loss, improved cardiovascular health, and stress relief. The possibility of obtaining such positive outcomes makes it no surprise that the number of runners and running events continues to progressively increase. As the sport continues to gain popularity, the dermatologic issues associated with running are more frequently encountered. For example, one study reported that more than 20% of injuries found among marathon runners are related to the skin.¹ While many of these skin findings are benign in nature, few can limit physical activity or become life-threatening. For this reason, dermatologists should be aware of such conditions in order to reduce the morbidity in this growing population. Therefore, this review discusses the risks, causes, presentations, treatments, and prevention of common dermatologic findings in runners. 

Traumatic
Blisters. Blisters are a common finding in runners, with a reported range of 0.2% to 39.0% in marathon runners according to a meta-analysis by Mailler-Savage and Adams.¹ Risk factors for developing blisters include poorly fitting shoes, heat, wet socks or shoes due to perspiration or precipitation, and excessive training.^1,2 These conditions lead to excess friction, resulting in horizontal forces that split the epidermis, allowing for the accumulation of fluid and blood.^1,2 

Clinically, blisters present as painful, well-defined bullae, most frequently seen at pressure points at the distal toes, underneath the metatarsals, and behind the calcaneus.¹ The blister may contain a clear or serosanguinous fluid, giving a range in coloration from clear to purple (Figure 1). 

While prevention is key to reduce blister formation, treatment includes draining the lesion using sterile equipment while keeping an intact blister roof. This prevents infection and limits pain and slower healing.³ Alternatively, if the blister is left alone, the fluid will continue to cause pain and potentially lead to blister enlargement.⁴ Once drained, patients should apply an antibacterial ointment (eg, mupirocin ointment) or petrolatum jelly with an occlusive dressing so that activity may be resumed.² 

Prevention includes wearing proper-fitting shoes to minimize movement of the foot within the shoe. The use of moisture-wicking sports socks; topical dressings, such as duct tape or bandages; emollient ointments; and antiperspirants can reduce excessive moisture while also relieving pressure points at areas prone to blistering.²

Jogger’s nipples. Jogger’s nipples are a form of chaffing that occurs due to friction forces between runners’ shirts and nipples. Two surveys found a range of 2% to 16.3% of runners reporting jogger’s nipples after running a marathon.^5,6 This form of chaffing is more common in women who run without a bra and men who run in shirts made of coarse fabrics. Cold weather also increases the risk for nipple chaffing, as cold temperatures lead to erect nipples, increasing their contact with clothing.¹ 

Clinically, patients present with painful, erythematous erosions over their nipples with possible fissuring and bleeding.⁷ Application of a petroleum jelly or antibiotic ointment is used as treatment. Wearing silk, semisynthetic, and soft fiber clothing decreases the incidence of nipple chaffing, and petroleum jelly or patches may also be used for prevention.⁷ 

Jogger’s toe. Jogger’s toe, which is due to repetitive trauma, is a form of subungual hematoma typically found on the longest toe of the foot. Running downhill can predispose runners to this condition, as this leads to more distressing contact to the long toe^.7 

Clinically, black discoloration of the hallux, distal second toe, or lateral aspects of the third, fourth, or fifth toes is found.⁷ This condition is usually self-limited and does not require treatment. Prevention includes wearing properly fitting footwear to minimize traumatic forces.⁷

Runner’s rump. Gluteal cleft hyperpigmentation due to constant contact between the sides of the buttocks during running strides constitutes runner’s rump.¹ Certain runners may be more prone to this condition depending upon their stride. There is no specific treatment for this condition, as it self-resolves when running is decreased or stopped.¹

Talon noir. Talon noir is a term used to define groups of blue-black- or brown-colored macules over the heel.^1,2 It results from repetitive shearing forces on the heel causing damage to dermal capillaries and ultimately intraepidermal and intracorneal bleeding.² 

Risk factors include movements leading to these shearing forces, such as stop-and-start motions, direction changes, and trauma to the heel from the back of shoes. These lesions, like jogger’s toe, can be differentiated from melanoma by paring with a sharp blade and removing the old hemorrhage. However, in some cases, biopsy is necessary to rule out a melanocytic lesion.² Lesions are typically self-resolving within 2 to 3 weeks, and prevention can be obtained by wearing proper footwear, skin lubricants, or extra socks or heel cups for cushioning.^1,2 

Subungual hematoma. Repetitive trauma to the nail bed is responsible for causing subungual hematomas. Pressure forces at the nail bed can result in the accumulation of blood in the area, leading to a hematoma. Clinically, this appears as an acutely painful area of discoloration at the nail plate (Figure 2).² A history of recent running or physical activity is usually sufficient for diagnosis; however, a biopsy can rule out pigmented tumors if uncertainty exists.² 

Subungual hematomas are self-limited, but healing may take up to several months. Evacuation of the underlying blood may be performed for rapidly expanding hematomas to prevent loss of the nail. This may be completed using a variety of tools, such as a heated paper clip, hot 18-gauge needle, scalpel blade, or dental drill to create an opening in the nail plate to allow the blood to drain.^2,3 The most important preventive measures are to avoid excessive exercise and wear properly fitting footwear. 

Infections
Tinea pedis. Tinea pedis, commonly referred to as athlete’s foot, is a well-known foot infection among runners. One study performed among marathon runners found that 22% of these athletes reported a positive fungal foot culture.⁸ In a similar study, Lacroix et al⁹ found positive fungal foot cultures in 31% of runners after collecting skin scrapings. The Achilles survey, which conducted clinical exams on 87,793 participants, found that individuals who were sports-active were approximately twice as likely to develop tinea pedis when compared with nonactive individuals.¹⁰  

The organisms most frequently responsible for tinea pedis are Trichophyton rubrum and Trichophyton mentagraphytes.¹¹ Risk factors for infection among athletes include trauma, occlusion, epidermal maceration from sweating, and use of community showers.¹¹ 

The clinical manifestations of tinea pedis vary depending upon the causative organism.  Runners may present with scaling of the lateral sole, erythematous scales at the interdigital areas, or vesicles along the medial instep of the foot. Patients may report symptoms of redness, itching, and scaling or blistering of the skin.² 

Treatment for tinea pedis includes the use of topical antifungal creams (eg, azoles or topical terbinafine) along with proper foot and shoe hygiene.¹¹ Preventive measures in athletes include the use of well-ventilated socks and shoes, wearing sandals in showers and other communal areas, removing moist socks after exercise, and applying powder to feet before exercise.¹ 

Onychomycosis. Onychomycosis, a fungal infection of the nail, is also common among runners. The Achilles survey found that the odds of developing onychomycosis were 1.5 times greater among active individuals than nonactive individuals in children and elderly.¹⁰ T rubrum and T mentagrophytes are the most commonly implicated dermatophytes causing this condition.¹² 

Clinically, the distal nail is affected and appears thickened and yellow. If the infection is severe, there may also be onycholysis or subungual debris.¹² Diagnosis may be difficult, as onychomycosis can be hard to distinguish from toenail changes as a result of regular activity, psoriasis, lichen planus, or other skin conditions that affect the nails. Potassium hydroxide examination of nail scrapings or subungual debris can be used for definitive diagnosis. 

Standard systemic therapy includes oral terbinafine or itraconazole. These therapies are widely used due to their high efficacy as compared with topical therapies and low costs. In certain patients, topical therapies may be a sensible choice, such as ciclopirox 8% nail lacquer, efinaconazole 10% solution, and tavaborole 5% solution.¹³ Unfortunately, cure rates can be very low, making oral therapies a better treatment option if no contraindications exist.¹² 

Athletes may reduce their risk of developing onychomycosis by wearing moisture-wicking socks during exercise with prompt removal of wet socks. Wearing shoes or sandals in showers or common areas is also preventive, as transmission of dermatophytes is high in these locations.¹²  

Plantar warts. Human papillomavirus is responsible for causing plantar warts. While there are a lack of epidemiological studies, several factors associated with exercise can predispose runners to plantar verrucae, including trauma and perspiration related maceration of the epidermis.¹ Differentiating running-related calluses from warts is important, as these conditions may appear clinically similar. Additionally, callused skin may harbor plantar warts and should be examined carefully for the presence of capillary thromboses after paring of the lesion.^1,12 

Plantar verrucae clinically present as hyperkeratotic, endophytic papules with sloped sides and a central depression on the soles of the feet.¹⁴ They may also coalesce into larger plaques, forming a mosaic wart.¹⁴ When present on the soles, patients may report pain and limited physical activity.¹ 

Treatment aims to destroy the wart using cryotherapy or through application of topical agents such as cantharidin or keratolytic agents (eg, salicyclic acid or tricholoroacetic acid).¹² However, in runners, these treatments may prevent timely return to activity. Therefore, topical imiquimod with occlusion is an effective treatment for athletes.¹ Paring of the verrucae may also be used to reduce pain.¹ To prevent transmission of the virus, athletes should keep their feet dry and wear shoes or sandals in common areas.¹²  

Environmental
Frostbite. Runners that brace cold weather without the proper precautions are at risk for developing frostbite. This typically occurs on unprotected areas of skin, such as the nose, cheeks, or ears when they are exposed to below-freezing temperatures. Initially, the affected area becomes numb and discolored (ie, blue-purple). Swelling, stinging, or burning may also occur. After 24 to 36 hours, a blister may develop, which usually resolves in an additional 2 weeks.¹ 

Treatment involves rewarming of the affected area in a 38 °C to 44 °C water bath for 20 minutes.¹ To avoid damage from recurrent cycles of freezing and thawing, rewarming should not be performed if the skin will be re-exposed to freezing temperatures.¹² In the case of blister formation, some authors suggest the drainage of clear blisters but not hemorrhagic blisters.^12,15 

Elevation of the affected area, tetanus prophylaxis, topical aloe vera, pain management, and nonsteroidal anti-inflammatory drugs (NSAIDs) should be used to promote healing.^12,15 Patients suffering from severe wounds should be treated expectantly to allow for wound demarcation followed by surgical debridement or amputation if indicated.¹⁵ 

Frostbite can be avoided by wearing sufficient clothing for the outdoor temperature. It is wise to layer loosely fitted clothing, as the air between layers may act as an insulator. Wet clothing should be changed promptly. Additionally, applying heavy lotions or creams before running can help to trap heat near the skin and preserve warmth.¹ 

Skin cancer. The increased amount of sun exposure seen in outdoor runners is concerning, as exposure to UV radiation increases risk for sunburns and skin cancers. The cumulative amount of UV exposure in a lifetime increases the risk for basal cell carcinoma, squamous cell carcinoma, and melanoma.¹² A study performed at the Ironman Triathlete World Championships found that despite wearing water-resistant SPF 25+ sun protection, all participants developed a sunburn following the competition.¹⁶ An observational cohort study targeting marathon runners discovered they had higher referral rates for removal of skin lesions concerning for nonmelanoma skin cancer when compared with nonrunners.¹⁷ The same study also found that marathon runners had higher rates of atypical melanocytic nevi and solar lentigines than the control group, which are strong indicators for an increased risk for malignant melanoma.¹⁷  

Most sunburns present as sharply demarcated areas of erythema that can be easily diagnosed upon examination. More advanced burns may have blistering and, if severe, may present with fever, chills, and nausea.¹² Once sunburns have been acquired, the damage caused to the skin cannot be reversed. Minor burns can be treated with cool water or a Burrow’s compress.¹ Blistering sunburns may require a nonsteroidal anti-inflammatory drugs for pain control as well as topical petrolatum jelly, warm soaks, menthol-containing lotions, or topical corticosteroids.¹ The key to decreasing sunburns and skin cancer risk in athletes is prevention. Athletes should make certain to use sunscreen with an SPF of 30+ consistently, wear photo protective clothing, and avoid sun exposure when possible, especially during hours of peak UV radiation (ie, 10:00 am-4:00 pm).¹² 

Other
Urticaria and exercise-induced anaphylaxis (EIA). Physical urticarias have been reported in 14% of athletes, with cholinergic urticaria being common in runners.^1,2 This form of urticaria occurs in response to body heat generated by exercise, stress, and environmental temperature.¹ Affected runners present with small, well-demarcated, pruritic wheels appearing 2 to 30 minutes into exercise. Antihistamine use before exercise in individuals who are affected is the treatment of choice.¹ 

EIA is a more severe, life-threatening form of physical allergy that can occur in runners. The risk of this condition is highest in individuals with preexisting food allergies and literature suggests that eating before running may predispose athletes to EIA.¹ The mechanism by which EIA occurs is still unclear, but it is hypothesized that mediators such as IgE, lactate, or creatinine phosphokinase released during exercise cause mast cell degranulation and resultant high levels of histamine.¹¹ The initial symptom is typically pruritis with or without a coexisting skin rash. EIA may then progress to cause angioedema, urticaria, gastrointestinal symptoms, respiratory symptoms, and respiratory or vascular collapse.¹¹ 

Treatment is aimed at providing vascular and respiratory support while administering antihistamines and epinephrine. EIA can be avoided by refraining from eating right before exercise and abstaining from exercising in extremely hot, cold, or humid weather.¹⁸ It has also been found that avoiding aspirin or NSAIDs before exercise reduces episodes of EIA. Runners with EIA should be counseled not to run alone and to carry epinephrine during exercise.¹

Conclusion
The most common skin disorders seen in runners vary greatly in their origin, presentation, prognosis, and management. It is important for dermatologists to be able to recognize and diagnose the discussed conditions as to provide patients with both timely and accurate treatments.

Ms Hunt is a medical student at University of Illinois at Chicago, College of Medicine. Dr Ashack is practicing dermatologist at Dermatology Associates of West Michigan and Assistant Professor at Michigan State University College of Human Medicine

Disclosure: The authors report no relevant financial relationships.

References
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3. Cohen PR, Schulze KE, Nelson BR. Subungual hematoma. Dermatol Nurs. 2007;19(1):83-84.

4. Basler RS. Skin injuries in sports medicine. J Am Acad Dermatol. 1989;21(6):1257-1262. doi:10.1016/s0190-9622(89)70340-6

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10. Caputo R, De Boulle K, Del Rosso J, Nowicki R. Prevalence of superficial fungal infections among sports-active individuals: results from the Achilles survey, a review of the literature. J Eur Acad Dermatol Venereol. 2001;15(4):312-316. doi:10.1046/j.0926-9959.2001.00289.x

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12. Adams BB. Sports Dermatology. Springer; 2006.

13. Lipner SR, Scher RK. Onychomycosis: clinical overview and diagnosis. J Am Acad Dermatol. 2019;80(4):835-851. doi:10.1016/j.jaad.2018.03.062

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17. Ambros-Rudolph CM, Hofmann-Wellenhof R, Richtig E, Müller-Fürstner M, Soyer HP, Kerl H. Malignant melanoma in marathon runners. Arch Dermatol. 2006;142(11):1471-1474. doi:10.1001/archderm.142.11.1471

18. van der Worp MP, ten Haaf DSM, van Cingel R, de Wijer A, Nijhuis-van der Sanden MW, Staal JB. Injuries in runners; a systematic review on risk factors and sex differences. PLoS One. 2015;10(2):e0114937. doi:10.1371/journal.pone.0114937