Overview
A jellyfish sting occurs when the tentacles of a jellyfish release venom through microscopic barbed cells called nematocysts, which inject toxins into the skin. These stings can cause pain, redness, itching, and in severe cases, systemic reactions like difficulty breathing or cardiac issues.

Why It’s Important
Jellyfish stings are common in coastal and tropical areas. While most are mild and self-limiting, some species, such as the box jellyfish or Portuguese man o’ war, can cause life-threatening reactions if not treated promptly.

Quick Facts

• Over 150 million jellyfish stings occur worldwide each year.

• The severity depends on the species, amount of venom, and individual sensitivity.

• Children and people with allergies may experience stronger reactions.

• Immediate first aid can significantly reduce pain and complications.

What Happens in the Body

• Jellyfish tentacles contain nematocysts that inject venom into the skin.

• The venom triggers an inflammatory and immune response, causing pain, swelling, and redness.

• Severe venom can affect the nervous system, heart, and skin tissues, leading to systemic symptoms.

Common Signs and Symptoms

• Sharp, burning, or stinging pain at the contact site

• Red or purple welts resembling whip marks

• Itching, swelling, or numbness

• Muscle cramps or spasms

• Nausea, vomiting, or dizziness in moderate cases

• Shortness of breath, chest pain, or collapse (in severe cases)

Diagnosis

• Based on history of ocean exposure and visible skin lesions

• Identification of jellyfish species (if possible) can guide treatment

• In severe cases, vital signs, ECG, and lab tests may be used to assess systemic involvement

Treatment and Management

• Remove tentacles with tweezers or gloved hands, avoid scraping with bare skin

• Rinse with vinegar (acetic acid) to neutralize nematocysts (for most species except Portuguese man o’ war, use seawater instead)

• Avoid freshwater, which can trigger more venom release

• Immerse area in hot water (104–113°F or 40–45°C) for 20–45 minutes to relieve pain

• Pain relievers (ibuprofen, acetaminophen) and antihistamines for itching

• Severe reactions may require:

  • Epinephrine (for anaphylaxis)

  • Intravenous fluids and oxygen

  • Antivenom (for box jellyfish stings)

Risks and Complications

• Allergic reactions or anaphylaxis

• Scarring or hyperpigmentation at the sting site

• Cardiac arrest or respiratory distress (in severe cases)

• Secondary infections if the wound is not cleaned properly

Who Is at Risk

• Swimmers, divers, and surfers in jellyfish-prone waters

• People in tropical and subtropical regions

• Children and those with weakened immune systems

• Individuals allergic to marine venoms or insect stings

Related Conditions

• Anaphylaxis

• Marine envenomation syndromes

• Cellulitis (if secondary infection occurs)

• Post-inflammatory hyperpigmentation

When to See a Doctor

• Persistent pain, swelling, or redness after basic care

• Signs of systemic reaction (dizziness, shortness of breath, rapid heartbeat)

• Severe stings involving large areas, face, or genitals

• Children, elderly, or immunocompromised individuals who were stung

• Suspected box jellyfish or Portuguese man o’ war sting

Last Updated: October 5, 2025