Jellyfish strings come from the tentacle, which is a long stringy hanging from the fish. The cells contain nematocysts found the long tentacles that trail the bell-shaped jellyfish, and in some species on the bell itself. These cells inject a protein-based venom. The most dangerous reaction to jellyfish strings is the possibility of a severe allergic reaction. However, some species of jellyfish have venom strong enough to kill you even if you are not allergic.
The most common symptoms of a jellyfish sting include sharp pain, red skin marks, swelling, itching and throbbing pain in the infected area. Jellyfish stings are common for people while swimming, wading or diving. The venom, which is a neurotoxin, causes the burning sensation.