Seabather's eruption is an

itch An itch (also known as pruritus) is a sensation that causes a strong desire or reflex to scratch. Itches have resisted many attempts to be classified as any one type of sensory experience. Itches have many similarities to pain, and while both ...

ing

dermatitis Dermatitis is a term used for different types of skin inflammation, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened ...

caused by a

hypersensitivity reaction Hypersensitivity (also called hypersensitivity reaction or intolerance) is an abnormal physiological condition in which there is an undesirable and adverse immune response to an antigen. It is an abnormality in the immune system that causes im ...

to the immature

nematocyst A cnidocyte (also known as a cnidoblast) is a type of cell containing a large secretory organelle called a ''cnidocyst'', that can deliver a sting to other organisms as a way to capture prey and defend against predators. A cnidocyte explosively ...

s of

larval A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

-stage thimble jellyfish (''Linuche unguiculata''),

sea anemones Sea anemones ( ) are a group of predatory marine invertebrates constituting the order Actiniaria. Because of their colourful appearance, they are named after the '' Anemone'', a terrestrial flowering plant. Sea anemones are classified in the p ...

('' Edwardsiella lineata'') and other larval

cnidarians Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...

. The eruption is sometimes attributed to "sea lice" or "sea ants", but

sea lice Sea lice (singular: sea louse) are copepods (small crustaceans) of the family Caligidae within the order Siphonostomatoida. They are marine ectoparasites (external parasites) that feed on the mucus, epidermal tissue, and blood of host fish. Th ...

(Caligidae) are

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

parasites of fish only. It should not be confused with

swimmer's itch Swimmer's itch, cercarial dermatitis or schistosome dermatitis is a short-term allergic contact dermatitis occurring in the Human skin, skin of humans that have been infected by water-borne schistosomatidae, schistosomes, a type of Trematoda, fl ...

Symptoms and signs

Symptoms generally arise later after showering. It is unusual to notice the eruptions immediately. Symptoms can last from a few days up to, exceptionally, two weeks. The reaction is identified by severe itching around small red

papule A papule is a small, well-defined bump in the skin lesion, skin. It may have a rounded, pointed or flat top, and may have a umbilication, dip. It can appear with a Peduncle (anatomy), stalk, be thread-like or look warty. It can be soft or firm a ...

s 1mm to 1.5 cm in size on areas of skin that were covered by water-permeable clothing or hair during ocean swimming. Initial swimmer exposure to the free-floating larvae produces no effects, as each organism possesses only a single undeveloped nematocyst which is inactive while suspended in seawater. However, due to their microscopic size and sticky bodies, large concentrations of larvae can become trapped in minute gaps between skin and clothing or hair. Once the swimmer leaves the ocean, the organisms stuck against the skin die, and automatically discharge their nematocysts when crushed, dried out, or exposed to freshwater. This is why symptoms usually do not appear until the swimmer dries, or takes a freshwater shower, without removing the affected clothing.

Treatment

Treatment is symptomatic, with most affected using a topical anti-itch cream (

diphenhydramine Diphenhydramine, sold under the brand name Benadryl among others, is an antihistamine and sedative. Although generally considered sedating, diphenhydramine can cause paradoxical central nervous system stimulation in some individuals, particula ...

) and a cortisone solution (

hydrocortisone Hydrocortisone is the name for the hormone cortisol when supplied as a medication. It is a corticosteroid and works as an anti-inflammatory and by immune suppression. Uses include conditions such as adrenocortical insufficiency, adrenogenit ...

Incidence

Seabather's eruption is common throughout the range of ''

Linuche unguiculata The thimble jellyfish (''Linuche unguiculata'') is a species of cnidarian found in the warm West Atlantic Ocean, including the Caribbean. It is a tiny jellyfish with a straight-sided, flat-topped bell. This jellyfish is the most common cause of ...

'' in the

Caribbean The Caribbean ( , ; ; ; ) is a region in the middle of the Americas centered around the Caribbean Sea in the Atlantic Ocean, North Atlantic Ocean, mostly overlapping with the West Indies. Bordered by North America to the north, Central America ...

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

, and Gulf States. Cases were first identified in Brazil in 2001. The closely related ''

Linuche aquila ''Linuche aquila'' is a species of cnidarian found in the tropical and subtropical areas of the Pacific Ocean. It is very small and is commonly known as a thimble jellyfish because of its size and shape. The larvae can cause bathers to develop a ...

'', found anywhere between Malaysia, the Philippines and the east coast of Africa, is also known to cause the condition. Swimmers in

Queensland, Australia Queensland ( , commonly abbreviated as Qld) is a state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Australia and New South Wales to the west, ...

, have reported seabather's eruption during the summer months of the year. Swimmers at the east-coast beaches of

Auckland Auckland ( ; ) is a large metropolitan city in the North Island of New Zealand. It has an urban population of about It is located in the greater Auckland Region, the area governed by Auckland Council, which includes outlying rural areas and ...

and the rest of the

Hauraki Gulf The Hauraki Gulf / Tīkapa Moana is a coastal feature of the North Island of New Zealand. It has an area of 4000 km2,Immune system disorders Parasitic infestations, stings, and bites of the skin