The term “sea lice” is a common misnomer for the tiny, transparent larval forms of certain jellyfish and sea anemones that cause a skin reaction known as seabather’s eruption. These larvae are free-swimming organisms that float in the ocean’s surface waters, unrelated to parasitic fish or human lice. This article focuses on the duration of the resulting rash and how to manage and prevent this intensely itchy condition.
Understanding the Source of the Rash
The reaction, formally called seabather’s eruption, begins when microscopic larvae become trapped against the skin, typically in areas covered by swimwear or body hair. These larvae possess stinging cells called nematocysts, which are coiled, venom-filled structures. Pressure, friction, or exposure to fresh water causes these nematocysts to fire, injecting a small amount of toxin into the skin.
The body’s immune system responds to this venom, resulting in a rash that is essentially an allergic reaction. The rash usually appears as small, red, intensely itchy bumps that can sometimes blister or resemble acne, often concentrated under the lines of a bathing suit.
Typical Duration and Factors Affecting Recovery
The timeline for a sea lice rash to resolve varies widely depending on the severity of the initial exposure and the individual’s immune response. For mild cases, the intense itching and rash generally begin to subside within three to seven days.
In more severe reactions, the rash can last for two weeks, and symptoms may linger for up to four weeks or longer. Factors influencing duration include the total number of stings received and the person’s specific sensitivity to the venom. Children often experience a more pronounced reaction, sometimes accompanied by systemic symptoms like fever or nausea, which can delay recovery.
A significant factor in recovery is whether post-swim protocols were followed, as remaining larvae trapped in swimwear can continue to fire nematocysts and re-expose the skin. Scratching the irritated areas also prolongs healing by breaking the skin barrier, increasing the risk of a secondary bacterial infection. If an infection occurs, the rash will take significantly longer to clear and requires professional medical attention.
Treating the Symptoms for Faster Relief
Actionable steps immediately after exposure help neutralize unfired stinging cells and reduce the severity of the rash. Remove contaminated swimwear immediately after leaving the water, and before taking a fresh water shower. Since fresh water can trigger remaining nematocysts to fire, gently rinsing the skin with clean saltwater is recommended first.
Symptom management focuses on reducing inflammation and controlling intense itching once the swimwear is removed. Over-the-counter treatments, such as a 1% hydrocortisone cream, can be applied two to three times daily to minimize discomfort. Taking an oral antihistamine also provides relief by calming the body’s allergic response.
Cool compresses or ice packs wrapped in a cloth can be applied to soothe the heat and itching. Avoid scratching while the rash is present, as this can lead to skin damage and potential infection. Seek medical attention if you notice signs of a severe reaction, such as difficulty breathing, or signs of infection, including increased warmth, pus drainage, or a high fever.
Steps to Prevent Future Exposure
Preventing seabather’s eruption relies on proactive awareness and careful post-swim hygiene. Before swimming, check local health reports or beach warnings, as outbreaks are often seasonal (typically peaking from March through August). Avoid swimming when local advisories indicate the presence of stinging organisms.
Immediately upon exiting the ocean, change out of your swimwear to prevent larvae from being pressed against your skin. Do not rinse off with fresh water while still wearing the swimsuit, as the change in salinity can cause trapped nematocysts to discharge their venom. Applying diluted vinegar or rubbing alcohol to covered skin areas before showering can help deactivate unfired stinging cells.
Thoroughly washing all exposed swimwear is crucial to ensure no larvae remain. Garments should be washed in hot, soapy water and then dried using a heated dryer cycle, since air-drying may not be sufficient to kill trapped nematocysts.