Vesicle
Formal Definition
A small, fluid-filled blister measuring less than 1 cm in diameter, containing clear serous fluid and arising from the epidermis; a primary skin lesion that characterizes certain viral infections (herpes simplex, varicella-zoster, hand-foot-mouth disease), contact dermatitis, and other conditions.
How It's Used on the Ward
"Little blisters" or "vesicular rash" — the descriptor for small fluid-filled bumps that look like tiny water droplets on skin.
Example
""62-year-old immunocompromised patient with unilateral dermatomal band of erythema and vesicles from T4 to T6 on the left — classic shingles. Starting valacyclovir and covering for post-herpetic neuralgia prevention.""
Clinical Context
Lesion size distinguishes vesicles (<1 cm) from bullae (>1 cm). Classic vesicular conditions: varicella (chickenpox) — scattered crops, all stages at once; herpes zoster (shingles) — unilateral dermatomal, very painful; HSV-1/2 — clustered vesicles on erythematous base; dyshidrotic eczema — lateral fingers/palms. When vesicles rupture, they leave erosions and crusting. In suspected herpes zoster, start antivirals within 72 hours of rash onset for maximum efficacy.
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