What Are the Effects of a Jellyfish Sting?

Jellyfish are members of phylum Cnidaria. They are predators and their long trailing tentacles are the weapons they use to stun their prey. The tentacles are equipped with cnidoblasts, stinging cells that eject a barbed, coiled thread carrying a paralyzing toxin into the jelly's victim. The effects of the sting depend on the species of jellyfish. According to "Oceanography, An Invitation to Marine Science," one species, the sea wasp, can kill a human in three minutes and is believed to have killed more people than sharks.

Box Jellyfish

• The box jellyfish is infamous as the most toxic jellyfish on Earth. Initial effects of a box jellyfish sting may include headache, fever, vomiting, and kidney failure. Death can sometimes follow within minutes and is usually caused by cardiac and respiratory arrest. Many cases of encounters with the box jellyfish, however, are relatively mild -- often because the stings from the tentacles did not fully penetrate the skin.

Irukandji Sydrome

• Irukandji syndrome is the name for a condition exhibited by some victims of a tiny jellyfish called the Irukandji jellyfish or Carukia barnesi. Patients develop low back pain, abdominal pain, vomiting, sweating, restlessness, fast heart beat and high blood pressure about thirty minutes after exposure. These symptoms may eventually progress to cardiac failure.

Anaphylactic Shock

• In some patients who are allergic, jellyfish stings can cause anaphylactic shock -- much like the symptoms associated with allergies to bee stings. In these cases it is the reaction of the patient's immune system, not the jellyfish toxin itself, that causes the problem. The patient's blood pressure drops rapidly, breathing airways become constricted causing wheezing, a skin rash develops, and vomiting usually occurs. Anaphylactic shock caused by jellyfish stings is extremely rare but life-threatening when it does occur.

Other Reactions

• Although some species of jellyfish like the box jelly are extremely dangerous, most jellyfish stings are painful but not life-threatening. The site of the sting may be acutely painful and a rash will usually develop that features itchy dark red bumps that look like blisters. These may last for hours or even days afterward. According to eMedicine, adding vinegar to the site of the sting is an effective initial treatment.