What are the typical physical exam findings for a friction blister in an individual, likely an athlete, who has recently engaged in an activity causing repetitive friction on the skin?

Physical Exam Findings for Friction Blisters

A friction blister presents as a fluid-filled elevation of the skin, typically tense and filled with clear serous fluid, located over areas of repetitive mechanical stress such as the heel, forefoot, or toes. 1

Primary Examination Findings

Blister Characteristics

• Fluid-filled elevation measuring the size in centimeters (document exact dimensions) 1
• Tense or flaccid appearance based on the degree of fluid distension within the blister cavity 1
• Clear serous fluid filling the blister space, distinguishing it from hemorrhagic or purulent lesions 2
• Intact or ruptured roof - note whether the overlying epidermis remains intact or has deroofed to create an erosion 1

Location and Distribution

• Predictable anatomic sites including the heel, ball of the foot, toes, or any area subjected to repetitive shear forces 3, 4
• Skin with thick horny layer and tight attachment to underlying structures (palms, soles) are most susceptible 4
• Single or multiple lesions - document the number and precise anatomical location using landmarks 1

Surrounding Skin Assessment

• Normal-appearing skin at the base in uncomplicated friction blisters (not arising on erythematous or inflamed skin) 1
• Absence of surrounding erythema, warmth, or edema in simple friction blisters, which would suggest secondary infection or alternative diagnosis 1
• Underlying callus or hyperkeratosis may be present at sites of chronic friction 5

Associated Clinical Features

Symptom Documentation

• Pain level - friction blisters typically cause localized discomfort, particularly with continued pressure or ambulation 1
• Absence of systemic symptoms - no fever, malaise, or constitutional symptoms in uncomplicated cases 5
• Functional impairment - document any limitation in weight-bearing or activities of daily living 1

Predisposing Factors to Document

• Recent activity history - new or increased running, hiking, military training, or sports participation 3, 6
• Ill-fitting footwear or new shoes not properly broken in 4, 6
• Moist environment - excessive sweating or wet conditions that promote blister formation 4
• Biomechanical abnormalities of the foot that create abnormal pressure distribution 4

Body Surface Area Calculation (When Multiple Blisters Present)

• Grade 1: <10% BSA involvement, asymptomatic or minimally symptomatic 5, 1
• Grade 2: 10-30% BSA with blisters affecting quality of life 5, 1
• Grade 3-4: >30% BSA with associated pain and functional limitation 5, 1

Critical Distinguishing Features

What Friction Blisters Are NOT

• No mucous membrane involvement - absence of oral, ocular, genital, or perianal lesions distinguishes from autoimmune bullous diseases 1
• No pustules or purulent drainage in uncomplicated cases 1
• No dusky erythema or painful surrounding skin that would suggest severe cutaneous adverse reactions 5, 1
• No spontaneous appearance - friction blisters have clear mechanical etiology from repetitive shear deformation 3

Documentation Essentials

Record the following systematically 1:

• Exact size in centimeters
• Precise anatomic location
• Tense versus flaccid character
• Intact versus ruptured roof
• Presence or absence of surrounding inflammation
• Associated pain level
• Predisposing mechanical factors identified
• Consider serial photography for monitoring progression if multiple lesions present 1