Wilderness: Jellyfish Sting

Medically Reviewed by Stephanie S. Gardner, MD on April 26, 2022
Written by WebMD Editorial Contributors
3 min read

Jellyfish are free-swimming, bell-shaped, gelatinous creatures with tentacles that may be more than 3 feet in length. Jellyfish that are harmful to humans are distributed throughout the world. They are found near the surface of the water during times of diminished light. Harmful jellyfish have stingers (nematocysts) capable of piercing the skin.

Other creatures with nematocysts include Portuguese man-of-war, sea wasps, anemones, and fire corals. These organs function long after the animal is dead.

Venoms include various substances, some of which trigger allergic reactions. The most toxic nematocystic animals are found along the Indo-Pacific and Australian waters.

  • Symptoms include intense, stinging pain, rash, and wheals (raised welts).
  • The progressive effects of a jellyfish sting may include nausea, vomiting, diarrhea, lymph node swelling, abdominal and back pain, fever, chills, and sweating.
  • Severe reactions can cause difficulty breathing, coma, and death.
  • Persistent redness and irritation after 2-3 days may signal bacterial infection of the wound.
  • Rinse with seawater. Avoid fresh water because it will increase pain. Do not rub the wound or apply ice to it.
  • For classic box jellyfish stings, apply topical acetic acid (vinegar) or isopropyl alcohol.
  • Remove tentacles with tweezers.
  • Apply shaving cream or a paste of baking soda or mud to the wound. Shave the area with a razor or knife and then reapply vinegar or alcohol. The shaving cream or paste prevents nematocysts that have not been activated from discharging toxin during removal with the razor.
  • Immobilize the extremity because movement may cause the venom to spread.
  • Hydrocortisone cream may be applied 2-3 times daily to relieve itching. Discontinue immediately if any signs of infection appear.
  • Eye stings should be irrigated with 1 gallon of fresh water.
  • Mouth stings should be treated with 1/4 strength vinegar. Avoid vinegar if oral swelling or difficulty swallowing occurs.
  • For a box jellyfish sting, after treatment with vinegar or alcohol, use the pressure-immobilization technique.
    • The extremity should be wrapped with a bandage in a style similar to wrapping a sprained ankle.
    • Bind the limb firmly but do not stop the circulation. The fingers and toes should remain pink.
    • Leave bandages intact until medical personnel are available for treatment.
  • CPR may be necessary.
  • Severe symptoms, such as difficulty breathing and intense pain, require immediate medical treatment.
  • A doctor should be consulted about treatment with available medications.

jellyfish sting, nematocysts