Lip Blisters: Causes, Differential Diagnosis, and When to Seek Care

Lip blisters—fluid-filled vesicles on the vermillion border or mucosa—have a broad differential. Most are benign and self-limited, but some signal systemic or malignant disease.

Common Causes

Cause	Key Features
Herpes Simplex (HSV-1/2)	Prodrome (tingle) → clustered vesicles → ulcerate → crust. Recurrent. Most common.
Aphthous Ulcers (Canker Sores)	Single/multiple round ulcers, yellow-white base, red halo. Non-viral. Inside lip/cheek.
Sunburn (Actinic Cheilitis)	Lower lip > upper. Burning, swelling, vesicles. Chronic → precancerous.
Contact Allergy	Toothpaste (SLS, flavorings), lip balm (propolis, lanolin), foods, metals. Itchy, swollen.
Trauma	Bite, thermal burn, dental procedure. History clear.
Drug Eruption	Fixed drug eruption (recurrent same site), SJS/TEN (mucosal involvement + systemic).
Nutritional Deficiency	B2 (riboflavin), B3, B6, B12, iron, zinc — angular cheilitis, glossitis.
Autoimmune	Lupus (oral ulcers), pemphigus vulgaris (flaccid bullae, Nikolsky+), mucous membrane pemphigoid.
Malignancy	SCC (chronic ulcer, indurated), melanoma (pigmented). Rare but critical.

Red Flags for Urgent Evaluation

• Lesion >2 weeks without healing
• Progressive growth, induration, bleeding
• Immunosuppression
• Ocular involvement (HSV keratitis)
• Systemic symptoms (fever, weight loss, lymphadenopathy)

Diagnostic Approach

1. History: Timeline, triggers, meds, sexual history, immunosuppression.
2. Exam: Distribution, morphology, dermatomal? conjunctiva? skin elsewhere?
3. Tests: HSV PCR/viral culture (gold standard), Tzanck smear, biopsy (if suspicious), serology, patch testing (contact), nutritional panel.

Treatment Principles

• HSV: Oral valacyclovir/acyclovir/famciclovir (early = shorter). Topical less effective.
• Aphthous: Topical steroids (triamcinolone paste), sucralfate, laser.
• Allergic: Identify/avoid allergen; topical calcineurin inhibitors.
• Sun: SPF 30+ lip balm; treat actinic cheilitis (5-FU, imiquimod, laser, vermillionectomy).

Most lip blisters are HSV or trauma. But "wait and see" fails for malignancy. If it persists, biopsy.