The jellyfish says: a caress of mine will burn you but if I am from the tropics it can kill you
(by Nicola Simonetti) They don't sting, they don't bite, they don't scratch but they caress. A uritating caress, that of the jellyfish. Just touch the fascinating tentacles to feel pain, skin irritation, swelling and redness. Sometimes they don't even caress but they send their own message that "burns" through the liquid released through their filaments.
What to do? The pediatricians of the Bambin Gesù hospital in Rome provide suggestions regarding the children but - they say - that also apply to the adults ("Beware of jellyfish" - Argon media). The first thing to do is to calm the child and let him breathe normally. If you are close to the shore, get it out of the water. If you are out of the way, support the child and call attention to help, especially if the carer has come into contact with the jellyfish. Check that there are no parts of jellyfish remaining attached to the skin and, if necessary, gently remove them with your hands. If medications are not available, it may be useful to run sea water on the affected part to try to dilute the toxic substance not yet penetrated. 
The correct dressing of the irritated part consists in the application of astringent aluminum chloride gel. The astringent gel has an immediate antipruritic action and blocks the spread of toxins. This is a gel that you should bring with you and that can also be useful for mosquito bites. In the absence of this ointment, a cortisone cream can be used even if it has a more delayed effect (they come into action after 20-30 minutes from the application), that is when the maximum reaction should already be off naturally. Avoid scratching or rubbing the sand on the painful area. Do not use extemporaneous dressings with ammonia, vinegar, alcohol or lemon juice: they would make the situation worse.
If the skin reaction spreads immediately after contact and there are breathing difficulties, pallor, sweating and disorientation, call the 118 and explain what it is: you will receive instructions on what to do until the emergency room staff arrives.
The area of skin affected by jellyfish remains sensitive to sunlight and tends to darken rapidly. To prevent the skin from getting stained, antihistamine ointments should be avoided and the affected area should be covered, or well protected by a sunscreen, until the inflammatory ration has disappeared (no more than two weeks).
Particular attention to the most dangerous tropical species that can also release even lethal poison. Their tentacles contain, within specific cells, millions of nematocysts, which are deposited on the victim's skin following contact. The rupture of these cysts releases a mixture of proteins that, penetrating into the tissues, can give different effects, depending on the type of jellyfish. The dangerous "sea wasp" (jellyfish class) releases a poison with hemolytic, cardiotoxic, dermoneurotic effects. The contact with the tentacles immediately causes stinging pain, swelling, erythema, vesicles and very intense bubbles, figures that often have the appearance of lashes and can result in skin necrosis. Like some small Australian jellyfish, sea wasps can cause systemic effects on the heart and cardiorespiratory apparatus. Even the "caravel of the sea", with which one can run into, rarely, even in the Mediterranean (they move in procession tens of meters long and are easily identifiable so as not to end up near us), can cause relevant skin symptoms and to the expense of others organs up to the risk of death. Do not be alarmed and wet the skin with VINEGAR and seawater and remove any tentacle residues (preferably with tweezers). Do not be afraid, however, to use your bare hands (perhaps wet with vinegar) as they will have, at the most, "marginal" symptoms. Then, administer local or oral painkillers, ice packs or baking soda to apply to the skin. Better not to use vinegar in our seas that can cause adverse effects.