Seabather's Eruption from Jellyfish Larvae
You most likely experienced seabather's eruption caused by planulae larvae of the jellyfish Linuche unguiculata (thimble jellyfish), which are microscopic and cause intense itching in areas covered by swimwear after ocean exposure in Caribbean waters including Barbados and the Dominican Republic. 1, 2
Causative Organism
The primary culprit is Linuche unguiculata larvae, a scyphomedusa whose planulae (larval stage) are too small to be seen with the naked eye and become trapped under bathing suits, causing envenomation when compressed against the skin 1, 2
All three swimming stages of Linuche unguiculata (ephyrae, medusae, and larvae) can cause seabather's eruption, though larvae are the most common cause in the Caribbean, Gulf of Mexico, and Florida waters 2
The condition is colloquially called "sea lice," though this is a misnomer as the organisms are jellyfish larvae, not parasitic crustaceans 3
Clinical Presentation
Intensely pruritic (itchy) papule-erythematous dermatitis develops predominantly in areas covered by bathing costumes, where larvae become trapped and discharge nematocysts when compressed 1
Symptoms typically begin during or shortly after ocean exposure, with the torso being a primary affected area when leaning against objects (like your buoy) that may harbor larvae 1
The eruption is usually benign and self-limiting, though severe symptoms can occur in some individuals 3
Geographic Distribution
Your exposure in Barbados or the Dominican Republic is entirely consistent with seabather's eruption, as these Caribbean locations are endemic areas for Linuche unguiculata 1, 2
The condition is most frequent in Caribbean waters, Gulf of Mexico, and Florida coastal regions, with seasonal variation corresponding to jellyfish life cycles (typically January-June in Mexican Caribbean) 2
Treatment Considerations
While your question focuses on identification rather than treatment, the 2024 American Heart Association guidelines provide evidence-based management:
Hot water immersion (40°C/104°F) is the most effective treatment for jellyfish-related pain, though evidence quality is very low 4
Tentacle removal by lifting or pulling (avoiding manual contact) is reasonable, followed by seawater rinsing 4
Topical lidocaine cream (4-15% formulations) may provide pain relief if hot water is unavailable 4
Antihistamines and steroids are used for symptomatic relief of the pruritic dermatitis 3
Important Caveats
Do not confuse this with Irukandji syndrome, which is caused by different box jellyfish species (Carukia barnesi and related Carybdeid genus) and causes severe systemic symptoms including abdominal/back/chest pain, tachycardia, and hypertension—this is primarily an Australian phenomenon, though rare cases have been reported in Florida 5
The term "sea lice" is misleading and should be avoided in medical contexts, as it incorrectly suggests a parasitic crustacean rather than cnidarian larvae 3
Nematocysts can remain active on skin and clothing even after leaving the water, so contaminated swimwear should be thoroughly washed to prevent recurrent stings 2