Jellyfish tentacles contain microscopic barbed stingers. Each stinger has a tiny bulb that holds venom and a coiled, sharp-tipped tube. The jellyfish uses the venom to protect itself and kill prey.
When you brush against a tentacle, tiny triggers on its surface release the stingers. The tube penetrates the skin and releases venom. It affects the immediate area of contact and may enter the bloodstream.
Jellyfish that have washed up on a beach may still release venomous stingers if touched.
Types of jellyfish
While many types of jellyfish are relatively harmless to humans, some can cause severe pain and are more likely to cause a systemic reaction. These jellyfish cause more-serious problems in people:
Aug. 09, 2014
- Box jellyfish. Also called sea wasps, box jellyfish can cause intense pain. Life-threatening reactions — although rare — are more common with this type. The more dangerous species of box jellyfish are in the warm waters of the Pacific and Indian oceans.
- Portuguese man-of-war. Also called bluebottle jellyfish, Portuguese man-of-war jellyfish live mostly in warmer seas. This type has a blue or purplish gas-filled bubble that keeps it afloat on the water and acts as a sail.
- Sea nettle. Common in both warm and cool seawaters, sea nettles live along the northeast coast of the United States and are abundant in Chesapeake Bay.
- Lion's mane jellyfish. These are the world's largest jellyfish, with a body diameter of more than 3 feet (1 meter). They're most common in cooler, northern regions of the Pacific and Atlantic oceans.
- Auerbach PS, et al. Field Guide to Wilderness Medicine. 4th ed. Philadelphia, Pa.: Mosby Elsevier, 2013. https://www.clinicalkey.com. Accessed March 27, 2014.
- Cegolon L, et al. Jellyfish stings and their management: A review. Marine Drugs. 2013;11:523.
- Purcell JE. Jellyfish in Chesapeake Bay and nearby waters. NOAA Ocean Service Education. http://oceanservice.noaa.gov/education/lessons/stinging_sea_append.html. Accessed April 2, 2014
- Li L, et al. Interventions for the symptoms and signs resulting from jellyfish stings. Cochrane Database of Systematic Reviews. http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD009688.pub2/abstract. Accessed April 1, 2014.
- Ward NT, et al. Evidence-based treatment of jellyfish stings in North America and Hawaii. Annals of Emergency Medicine. 2012;60:399.
- Auerbach PS. In reply to evidence-based treatment of jellyfish stings in North America and Hawaii. Annals of Emergency Medicine. 2013;61:253.
- Lebwohl MG, et al. Treatment of Skin Disease: Comprehensive Therapeutic Strategies. 4th ed. Philadelphia, Pa.: Elsevier, 2014. https://www.clinicalkey.com. Accessed March 27, 2014.
- Marcus EN, et al. Jellyfish stings. http://www.uptodate.com/home. Accessed March 27, 2014.