Differential Diagnosis for Blistering Skin Rash after Beach

Single most likely diagnosis

• Herpes Simplex Virus (HSV) infection: This is the most likely diagnosis given the description of the rash resembling herpes, especially if the patient has a history of HSV outbreaks or if the rash is localized to a specific area such as the lips (cold sores) or genital area.

Other Likely diagnoses

• Contact Dermatitis: This could be due to exposure to irritants or allergens at the beach, such as certain plants, sunscreen, or insect repellents. The rash might appear as blisters or vesicles.
• Phototoxic or Photoallergic Reaction: Certain medications or substances can cause a skin reaction when exposed to sunlight, leading to blistering rashes.
• Impetigo: A highly contagious bacterial skin infection that can cause blisters or sores, often seen in areas exposed to the sun or after activities where skin-to-skin contact occurs.

Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)

• Stevens-Johnson Syndrome (SJS) or Toxic Epidermal Necrolysis (TEN): Although rare, these are life-threatening conditions usually triggered by medications or infections. They can start with blistering skin lesions and progress to widespread skin detachment and mucosal involvement.
• Erythema Multiforme: An immune-mediated disorder that can be triggered by infections (including HSV) or medications, characterized by target lesions, which can sometimes blister.

Rare diagnoses

• Bullous Pemphigoid: An autoimmune disease that causes blistering of the skin, more common in older adults.
• Pemphigus Vulgaris: Another autoimmune disease leading to blistering of the skin and mucous membranes, which is rare but serious.
• Marine-related infections (e.g., Vibrio vulnificus): While rare, individuals with open wounds exposed to contaminated seawater can develop severe infections, which might initially present with blistering lesions.