Jellyfish and corals have special stinging cells that are triggered on contact to shoot out and penetrate the skin of their prey. The intensity of these stings varies by species, and most are not harmful to humans. However, there are some species that inflict painful and possibly fatal stings to humans. Before you dive a new location, you should research the dangerous corals and jellyfish that are common in the area and avoid direct contact with them while diving.

Stinging cells cannot penetrate wetsuits, dry suits, and most diveskins, so you should wear some form of exposure suit even when it's not needed for thermal protection.