Unlike some tropical jellyfishes, the jellyfish which populate our seas cannot kill a person. In the case of a jellyfish sting you should prevent further spread of the injected toxin: do not scratch the irritated area, do not wash with fresh water, do not apply cold water or ice, do not apply vinegar, ammonia or alcohol compresses, do not remove any splinter of the tentacles with tweezers, it is better to use your hands.
To reduce the pain, wash the affected area with sea water and disinfect it with baking soda. The best remedy is the application of an astringent gel made with aluminum chloride, which has an immediate antipruritic action and blocks the spread of toxins. In extreme cases, use some cortisone cream and, if necessary, contact the clinic on the beach or the first aid station.