The short version
- “Sea lice” is the common name for seabather’s eruption, an itchy rash from tiny jellyfish larvae, most often the thimble jellyfish; real sea lice are fish parasites[1][3].
- The rash appears a few minutes to 12 hours after being in the sea, mostly under swimsuits, swim caps, fins and wetsuit cuffs[2].
- It usually clears in 10 to 14 days; antihistamines and 1% hydrocortisone control the itch[2][1].
- Take the suit off before rinsing: a freshwater shower with a contaminated suit on makes trapped larvae sting again[2].
What sea lice really are
The larvae are only 2 to 3 mm long and get trapped against the skin by fabric; pressure from the suit triggers their stinging cells[2][9]. Tomchik’s 1993 JAMA review linked the syndrome to larvae of Linuche unguiculata, carried ashore by ocean currents[1].
| Where reported | Cases | Finding |
|---|---|---|
| Florida, Caribbean, Gulf of Mexico | Long-standing hotspot | Outbreaks when larvae drift to shore[1][4] |
| Santa Catarina, Brazil, 2009 | 38 cases | Papules mainly under bathing suits[4] |
| Santa Catarina, Brazil, January 2012 | 14 cases in two weeks | Clustered at the height of summer[5] |
| Mediterranean Sea, 1987 to 2023 | 7 patients | First cases reported from the Mediterranean[7] |
Symptoms and how it gets misdiagnosed
| Feature | What to expect |
|---|---|
| Onset | A few minutes to 12 hours after swimming[2] |
| Rash | Raised red bumps or blisters, often extremely itchy[2] |
| Where | Under swimsuits, swim caps and fins, and along the cuffs of wetsuits and T-shirts[2] |
| Severe reactions | Fever, nausea, vomiting, headache, chills[2][3] |
| Duration | Usually 10 to 14 days[2] |
Brazilian clinicians have documented cases confused with fungal skin infection and parasitic infestations[6]. Diver’s dermatitis is a separate marine rash, and the history of where the rash sits is the main clue[8].
What to do after exposure
- Get the suit or wetsuit off first, and do not rub the skin, which makes larvae sting[2].
- Then shower with fresh water and soap, never with the contaminated suit on[2].
- Rinse the suit in vinegar or rubbing alcohol, then wash it in hot soapy water and dry it before wearing again; stinging cells can survive in dried fabric[2][3].
- Treat the itch: an antihistamine or 1% hydrocortisone cream; UF/IFAS cites hydrocortisone lotion 2 to 3 times a day for 1 to 2 weeks[2][3].
- An ice pack can ease the pain[2][3].
When the rash needs a doctor
Get medical advice for red streaks, pus, increasing swelling or warmth, or fever with no other cause[2]. Severe reactions with fever, chills and vomiting are treated with oral steroids[3]. At sea, that is a radio medical call, logged in the medical log.
Why it matters for crews and divers
The larvae lodge under swim caps, fins and wetsuit cuffs as well as swimsuits[2], so divers and crew who enter warm coastal water are exposed too. A quick suit-off, rinse and wash routine stops repeat stings from the same gear[2].
For diving operations, see commercial diving medical rules. For other skin problems from the sea, see fish handler’s disease and trench foot at sea.
Discovery Health MD writes practical skin and sting protocols for vessels and dive teams: maritime medical consulting for the protocol itself, and ship medical chest management for antihistamines and steroid creams in the chest. Ask a physician to review your marine skin protocol.
Common questions
What are sea lice?
The common name for seabather’s eruption, a rash caused by stinging jellyfish larvae; true sea lice are fish parasites[1][3].
What do sea lice bites look like?
Raised red bumps or blisters, very itchy, mostly in areas covered by a swimsuit[2].
How long does sea lice rash last?
Usually 10 to 14 days[2].
How do you treat sea lice rash?
Antihistamines and 1% hydrocortisone for itch, an ice pack for pain, and oral steroids for severe reactions[2][3].
Should you shower after sea lice?
Yes, but take the swimsuit off first; showering with a contaminated suit on makes the larvae sting[2].
Where do sea lice occur?
Mainly Florida, the Caribbean and the Gulf of Mexico, with cases also reported in Brazil and the Mediterranean[1][4][7].
Can divers get sea lice?
Yes. The larvae can collect under swim caps and fins and along wetsuit cuffs[2].
