What you should know before entering the water:
Jellyfish stings are a health hazard all-too-common for beach vacationers. Although most jellyfish stings are harmless (with some exceptions), which can be extremely painful. The results stinging sensation when stingers at the ends of the tentacles of jellyfish and other aquatic animals in contact with human skin, usually while wading or swimming in the ocean.
Jellyfish belong to different classes of invertebrates:
Hydrozoans (eg, Portuguese man of war and fire corals)
Scyphozoans, the "true" jellyfish and the most common
Cubozoans, for example, most toxic "Medusa"
Anthrozoans (sea anemones and corals, which are related to jellyfish, but they are very low toxicity to humans)
Jellyfish stings true (scyphozoans) are generally less toxic than those of the hydrozoans and cubozoans and usually result in injuries to those parts of the skin where contact with the tentacles produces. The skin is a red rash pain, itching, and suggested that may persist for days or weeks. It is possible that an allergic reaction to occur that further increase inflammation and the severity of the rash.
The sting of the Portuguese man of war is more painful than the common jellyfish. Some people have described the sting of the Portuguese man of war as a feeling of being beaten by lightning, and the sting has been responsible for two deaths. The Portuguese man of war is a major invertebrate whose tentacles can reach up to 100 feet long. Tentacles, whether in these animals are capable of causing stings to humans for up to two weeks.