In January 2017, a 28-year-old man presented with a 1-day history of burning and itching cutaneous lesions. He was concerned about the possibility of having acquired a communicable disease. The patient bathed and swam at Ipanema Beach (22°59′01″S; 43°12′16″W), Rio de Janeiro, the previous 4 consecutive days. On examination, around 30 erythematous papules and macules were distributed in a male swimwear pattern (Figure 1). No systemic symptoms were observed. A topical corticosteroid cream was prescribed, with complete remission of the lesions 1 week later.
The rash was consistent with seabather’s eruption, a pruritic dermatitis occurring after contact with larvae of some marine animals, such as the thimble jellyfish Linuche unguiculata1. The planula larvae of this cnidarian are small enough (approximately 0.5mm) to pass through the fabric weaves of most swimwear and become trapped against the skin. External pressure or osmotic changes, including contact with freshwater, triggers the discharge of toxins by organelles called nematocysts. The diagnosis is established based on history of exposure to seawater followed by the appearance of rash in the peculiar topography of the areas covered by the bathing suit1.
Possible preventive measures include the use of sunscreen under the swimwear, tight-weave (instead of open-weave) fabric, a female two-piece instead of one-piece swimsuit, and avoidance of T-shirts and showering with fresh water while wearing a contaminated suit. In Brazil, this marine envenomation is mainly reported in the coastal areas of São Paulo2 and Santa Catarina3 states. We are unaware of previous reports from the State of Rio de Janeiro.