Swimmer’s itch (cercarial dermatitis) is a temporary skin rash caused by microscopic parasites (cercariae). These parasites are released into the water by infected snails. The larvae mistakenly burrow into human skin, causing an allergic reaction before they quickly die, as humans are not their intended host.
Understanding Where Risk is Highest
The parasite’s presence is tied to specific environmental conditions. Risk increases significantly in shallow, near-shore areas where the host aquatic snails are most abundant. These snails thrive in areas with aquatic vegetation, such as weeds and reeds.
Warm water temperatures, common during summer, encourage infected snails to release cercariae more intensely. Onshore winds can also concentrate the parasites along the shoreline, increasing their density. Avoid bodies of water where warning signs are posted or where large numbers of waterfowl, the parasite’s final hosts, are present.
Creating Physical Barriers
Applying topical products creates a physical layer that hinders the parasite’s ability to penetrate the skin. Waterproof sunscreens are recommended because they establish a protective, non-porous film. The thicker consistency makes it difficult for cercariae to successfully burrow.
Thick, greasy substances like petroleum jelly or specialized lotions also serve as an effective barrier. These substances physically impede the parasite’s attachment and entry into the skin. Apply the protection liberally and evenly to all exposed skin before entering the water.
Immediate Post-Swim Protocol
The most effective prevention is physically removing the cercariae immediately upon exiting the water, before they burrow. Do not allow water droplets to evaporate naturally, as this stimulates the parasites to penetrate. Instead, immediately and aggressively towel-dry your entire body.
Vigorously rubbing the skin with a coarse towel helps dislodge and crush any attached cercariae. If possible, rinse the skin with clean, fresh water after leaving the lake or pond, and then dry off. Promptly remove any wet swimwear, as parasites can remain trapped in the fabric against the skin.
Treating the Reaction
If preventive measures fail and the itchy, pimple-like rash develops, focus on symptom management. Over-the-counter hydrocortisone creams reduce inflammation and relieve itching when applied to affected areas. Calamine lotion and other anti-itch lotions offer a cooling and soothing effect on irritated skin.
Oral antihistamines lessen the body’s allergic reaction, which causes the itching. Soaking in a bath with colloidal oatmeal or Epsom salts also provides temporary relief. Avoid scratching the rash, which could break the skin and introduce a secondary bacterial infection. Consult a healthcare provider if the rash is severe, persists beyond two weeks, or shows signs of infection like warmth or pus.