Seabather’s eruption

Are You Confident of the Diagnosis?

What you should be alert for in the history

Patients may present with a severe itching of the skin within 24 hours after salt-water exposure. In many cases, itching may keep the patient awake at night. Patients may report participating in water activities (eg, wading, surfing, snorkeling) in a location known for previous cases of seabather’s eruption.

Additionally, patients may describe observing black dots, small jellyfish, or nothing in the water during exposure. Some patients first notice a stinging sensation while still in the water, while others may notice the sensation as they leave the water. Patients may also have experienced similar eruptions in the past. Subsequent episodes may become more widespread and intense.

Characteristic findings on physical examination

Patients typically present with an intensely pruritic, erythematous maculopapular rash, which appears within 24 hours post-exposure. Lesions may progress to vesicles or pustules, and urticaria may be seen. The duration of the rash may range from days to weeks. Seabather’s eruption manifests in a swimming suit distribution (opposite to swimmer’s itch). Lesions tend to be more numerous in areas where clothing is tighter fitting (eg, waistband).

In men, the most common body parts affected (in descending order) are the buttocks, abdomen, and groin (Figure 1, Figure 2). In women, the chest, abdomen (especially if wearing a one-piece bathing suit), and buttocks are most affected (Figure 3). Primary lesions can range in diameter from 2 to 15 millimeters and all appear at same stage of development. Excoriation of lesions may lead to secondary skin infections or scarring. Systemic symptoms include fatigue, malaise, fever, nausea, and vomiting.

Figure 1.

A 10-year-old boy presented with an intensely pruritic eruption on the buttocks. (Photo courtesy of Amor Khachemoune, MD)

Figure 2.

A 10-year-old boy presented with an intensely pruritic eruption on the groin area. (Photo courtesy of Amor Khachemoune, MD)

Figure 3.

Mother of the 10-year-old boy with classic swimming suit distribution. (Photo courtesy of Amor Khachemoune, MD)

Expected results of diagnostic studies

Diagnosis of seabather’s eruption is based primarily on clinical suspicion. Histopathology from skin biopsy may demonstrate perivascular and interstitial inflammatory infiltrate consisting of predominantly lymphocytes and neutrophils with few eosinophils. Serologic tests are not commonly performed in the outpatient setting; however, several studies have employed enzyme-linked immunosorbent assays to confirm cases.

Diagnosis confirmation

Several conditions should be considered in the differential diagnosis of seabather’s eruption. Swimmer’s itch should be considered in the differential; however, it is classically associated with fresh water exposure and tends to affect areas of the skin that are not protected by clothing (opposite to seabather’s eruption). Other conditions to consider are hot tub folliculitis, arthropod exposure, contact dermatitis, and viral exanthems.

Hot tub folliculitis generally occurs following recent exposure to hot tub, whirlpool, swimming pool, or waterslide water. The patient will have diffusely distributed follicular lesions. Insect bites (mosquitoes, bed bugs, chiggers, scabies) present with patient history consistent with arthropod exposure. For contact dermatitis, patient reports a history consistent with poison ivy or other similar exposure. Lesions are limited to areas that have been in contact with foliage.

Skin manifestations of viral causes such as viral exanthems or more defined entities such as varicella/zoster, rubeola, rubella, herpes simplex, should be suspected if a patient is immunocompromised or has not received routine immunizations.

Who is at Risk for Developing this Disease?

Seabather’s eruption is endemic in certain parts of the world (Florida, Caribbean, Long Island, Brazil), though cases have been reported worldwide. Any person swimming in a body of saltwater, where cnidarians are known inhabitants, is potentially at risk. Groups particularly at risk are those who have previously been exposed, children under sixteen years, and surfers. Length of time in the water did not seem to significantly increase risk. After exposure, showering with swimwear taken off may be protective.

What is the Cause of the Disease?

Seabather’s eruption is caused by specific members of the phylum Cnidaria. A commonly implicated species is Linuche unguiculata (thimble jellyfish) in Florida and other locations. Edwardsiella lineate, a sea anemone, is also a known offender in the Long Island area of the United States.


Seabather’s eruption occurs when the larvae of Linuche unguiculata (or other cniadrian) become trapped on human skin (under clothing, in flexural areas or in skin folds) and release their nematocysts. Nematocysts may be released in response to mechanical stimulation/pressure (rubbing while drying with towel) or osmotic changes (rinsing with freshwater instead of saltwater). These stinging or “nettle” cells inject a toxin into the skin resulting in an intense inflammatory reaction.

Systemic Implications and Complications

Possible complications include secondary bacterial skin infections. Patients are at an increased risk when lesions are excoriated or manipulated. Standard treatment for secondary infection is topical or oral antibiotics.

Treatment Options

Treatment options for swimmer’s eruption are summarized in Table I.

Table I.
Medical Surgical Physical
TopicalCool compressesCooling lotions- menthol- calamineCorticosteroidsSystemicAnti-histaminesCorticosteroids Not applicable Not applicable

Optimal Therapeutic Approach for this Disease

Seabather’s eruption is a self-limiting process and is not contagious. Most cases only require symptomatic treatment. For mild cases, treatment consists primarily of home remedies such as cool compresses. The treatment ladder is similar to that of swimmer’s itch.

Table II. Treatment ladder for seabather’s eruption.

Table II.
If itching is moderate, a combination of mid-potency topical steroid, oral anti-histamine, and calamine lotion may be used.
Medication Dose, Route, Frequency
Mometasone Children >2 years of age and adults:(0.1%) apply topically sparingly to the affected area(s) once dailyand
Diphenhydramine Children:5 mg/kg/day orally given in divided doses every 6-8 hours when required, maximum 300mg/day;Adults:25-50mg orally every 4-6 hours when required, maximum 300mg/dayand
Calamine lotion: Children and adults:apply topically to the affected area(s) as required
Severe or refractory cases may benefit from oral corticosteroid.
Medication Dose, Route, Frequency
Prednisone Children and adults:1mg/kg/day orally for 1 week, followed by 0.5mg/kg/day for 1 week, followed by 0.25mg/kg/day for 1 week

Patient Management

Patients should be followed days to weeks after initial presentation to monitor possible complications and assess response to symptomatic therapy. The only way to completely eliminate the potential for seabather’s eruption is to avoid exposure to affected waters during peak seasons; this scenario is unlikely as beach-going is common during summer months when cnidaria larvae are numerous. Swimmers should be advised to wear looser fitting swimwear to avoid the larvae from becoming trapped between the skin and clothing as water drains (when exiting water).

Wearing less swimwear may be advantageous, but the swimmer must also consider the risk of increased UV exposure. Additionally, the use of sunscreen may create a physical barrier to nematocysts. One topical sting inhibitor cream, with chemical properties of the mucous coating of clownfish, has shown significant reduction (relative risk reduction of 82%) in envenomation in a small double-blind, randomized, placebo-controlled trial.

After activity in saltwater, one should remove swimwear and thoroughly rinse off the body (in unaffected saltwater, if available) and launder swimwear. Nematocysts may remain in swimwear even with rinsing and can potentially sting one’s skin subsequent times it is worn.

Unusual Clinical Scenarios to Consider in Patient Management

A patient could present with seabather’s eruption after re-wearing swimwear containing non-discharged nematocysts up to 2 weeks after the initial exposure.

What is the Evidence?

Wong, DE, Meinking, TL, Rosen, LB, Taplin, D, Hogan, DJ, Burnett, JW. “Seabather's eruption: clinical, histologic, and immunologic features”. vol. 30. 1994. pp. 399-406. (First article providing laboratory proof of seabather's eruption etiology. Detailed discussion of cause, pathology.)

Freudenthal, AR, Joseph, PR. “Seabather's eruption”. N Engl J Med. 1993. pp. 542-4. (Article reviewing case reports of Long Island seabather's eruption caused by E lineata.)

Sams, WM. “Seabather's eruption”. Arch Dermatol Syphilol. vol. 60. 1949. pp. 227-37. (Article first describing seabather's eruption in lower East Coast of Florida)

Kumar, S, Hlady, WG. “Risk factors for seabather's eruption: a prospective cohort study”. Public Health Rep. vol. 12. 1997. pp. 59-62. (Article identifies various risk factors and describes clinical presentation, treatment outcome, and preventative measures.)

Hunter, GW, Malloy, JF, Ullman, AF. “More seabather's eruption”. Am J Pub Health Nat Health. 1963. pp. 1413-17. (Article describes a seabather's eruption outbreak in Panama City, Florida. Review of two cases and discussion of differences between cercarial dermatitis and seabather's eruption.)

Khachemoune, A, Yalamanchili, R. “What is your diagnosis? Diagnosis: seabather's eruption”. Cutis. vol. 70. 2006. pp. 148-52. (Article provides review and classic clinical case with images.)

MacSween, RM, Williams, HC. “Seabather's eruption—a case of Caribbean itch”. Br Med J. vol. 312. 1996. pp. 957-8. (Article describes two confirmed cases of seabather's eruption in the Caribbean. Review of etiology, clinical picture, potential preventative measures.)

Haddad, V, Cardoso, JL, Siveira, FL. “Seabather's eruption: report of five cases in southeast region of Brazil”. Revista do Instituto de Medicina Tropical de São Paulo. vol. 43. 2001. pp. 171-2. (Article reports first known cases in Brazil, brief discussion of disease)

(Article provides therapeutic approach to cercarial dermatitis which may be generally applied to seabather's eruption.)

Boulware, DR. “A randomized, controlled field trial for the prevention of jellyfish stings with a topical sting inhibitor”. J Travel Med. vol. 13. 2006. pp. 166-71. (Article provides human data demonstrating protective benefit of a topical sting inhibitor based on the chemical makeup of clownfish.)