Contact with medusa



Bathing in the sea, swimming, playing or doing sports in your free time or on vacation are activities that have positive effects on the well-being of those who practice them.

Regardless of their quality, in the waters there can be fascinating, elegant and mysterious aquatic organisms, but unfortunately equipped with stinging systems, such as jellyfish, which can cause more or less serious effects on health.

Jellyfish are simple, invertebrate organisms, members of the phylum Cnidaria, which includes beautiful and colorful creatures such as sea anemones, gorgonians and corals; they have a life cycle in which a free form in the water alternates (the real, planktonic jellyfish) and the form that lives anchored to substrates such as rocks or algae (the so-called polyps).

The jellyfish have a bell shape, like an 'inverted octopus', which encloses a digestive cavity that functions both as a stomach and as an intestine, around the base of which threadlike tentacles start.

They are made up of three layers: an external one, called the epidermis; an intermediate consisting of a dense, elastic and gelatinous substance (mesoglea) composed of approximately 95% water; an inner layer, called the gastroderma.

They have a basic nervous system that allows them to smell, detect light, and respond to other stimuli. A jellyfish's body parts radiate from a central axis (radial symmetry) which allows jellyfish to detect the presence of food or respond to danger from any direction.

From an ecological point of view, jellyfish are important components of the marine food web and are the food of herbivorous fish in coral reefs, sea turtles and large fish in open water (pelagic environment).

In the last 20-30 years, phenomena of great proliferation of jellyfish (blooms) alternating with periods of fewer sightings have also been observed in our seas.

Although articles appear every year as summer approaches, indicating a progressive increase in jellyfish blooms, there is no complete agreement that jellyfish are increasing steadily and continuously, much less a shared explanation. on the reasons for this hypothetical increase. Various factors have been considered, such as the rise in sea temperature due to climate change, the phenomenon of overfishing which significantly reduces the predators of jellyfish, the increase in acidity of the water as a result of the increase in carbon dioxide. in the air. But also physical phenomena such as the presence of strong underwater currents that convey the jellyfish and bring them to the surface, where they concentrate and give rise to large blooms, or the presence of strong winds that help to group the organisms.

Jellyfish generally move vertically: from the surface they can descend to the bottom even for hundreds of meters and are carried away by currents, whose movement they cannot oppose.

Jellyfish are feared by bathers because their contact causes reactions on the skin, but they are not the ones to attack: generally it is the bathers who get too close to the animal and involuntarily bump into it.

We speak improperly of jellyfish sting: the jellyfish does not sting, nor does it bite, but in response to a potential danger its tentacles emit a stinging substance for the skin.

In fact, on the part of the tentacles farthest from the body there are highly specialized defense cells called cnidocytes inside which there are "bags" containing the stinging liquid (nematocysts), and small pointed spiral formations (spicules) kept under pressure and which function like small arrows.

Following the collision between a tentacle and a person, the nematocysts remain attached to the skin and the spicules release the stinging substances. Jellyfish with long tentacles (in some species they reach 10 meters in length!) Can have millions of nematocysts which subsequently to contact may remain on the skin of the victim, without immediately discharging the poison contained in. Do not remove them, it can cause irritation even after hours of contact.


The liquid of nematocysts contains substances consisting of amino acids such as tetramine, 5-hydroxytryptamine, histamine and serotonin, and heat-sensitive proteins, which can trigger allergic processes of varying severity.

When the tentacles touch the skin there is a sensation of strong burning and pain; Immediately after contact, the skin becomes irritated and signs such as red and swollen crossed lines (erythema and edema) form with the formation of small blisters.

The burning is not associated with a "burn, because the manifestations are the result of the irritating action of the toxins and begins to subside after 10-20 minutes, but an intense itching sensation remains.

In general, however, most of the effects due to contact with the jellyfish present in our seas are resolved in a few hours, with a simple skin reaction and a little pain.

The severity of the effects is highly variable and depends on:

  • by the affected person, the severity of the event may be related to age (children and elderly people are generally more sensitive), the extent of the affected body area, the person's health conditions and potential allergic reactions
  • the extent and duration of the contact, if greater than 50% of the surface of the body, the intensity of pain and burning can be so strong as to require medical attention
  • from the species of jellyfish, depending on the species, the effects can be more or less serious because the concentration and composition of the stinging liquid vary between species

Effects that can occur include:

  • local reactions, pain, irritation, dermatitis, which in the long term can cause pigmentation, scarring and thickening of the skin
  • allergies
  • persistent pain and internal organ effects, if the stinging substances enter the bloodstream (systemic effects). Although rare in our seas, pulmonary edema, blurred vision, vomiting, muscle aches and convulsions can occur.

In most cases, the disorders (symptoms) disappear within a few hours and there is no need for medical assistance.

Tropical jellyfish

It is important to know that in the tropical seas, the Australian coral reef, the Red Sea, some typical jellyfish (not present in the Mediterranean) can cause very serious effects, with severe pain, not necessarily localized at the point of contact with the jellyfish, which begins about a half an hour after being hit.

This reaction can be dangerous and requires immediate medical attention (first aid).

In rare cases, allergic reactions may occur, which require specific intervention.

In these areas, following contact with jellyfish some people have died from cardiac and respiratory arrest, renal failure and anaphylaxis: although these are very rare events, it is important, however, to remember that not all jellyfish are the same, especially when traveling. and take a beach holiday in exotic places.

Stinging jellyfish in the Mediterranean Sea

Most of the jellyfish found in the Mediterranean Sea are either harmless or very little irritating.

The following are the stinging ones:

  • Pelagia noctiluca, so called for its ability to emit luminescence, is the most widespread species in the Mediterranean. It is abundant in the Tyrrhenian and Adriatic and is typical of warm waters, but can easily survive in the more temperate and cold seas. It is mostly distributed vertically between 150 m depth and the surface, but during the day it can be found even further down (up to 1,400 m). It is a small pelagic jellyfish usually pink, mauve brown or light brown, with a phosphorescent bell measuring 3 to 12 cm in diameter in adults. In this species, nematocysts are widespread not only on the tentacles but also on the entire surface, therefore it can cause irritation even through contact with the bell, even once beached. It is very stinging but the effects are generally limited to the surface of the skin and cause only erythema, edema and blisters, with local pain that may persist for 1-2 weeks; complications to internal organs (systemic) are rare, while cases of severe allergy can occur with bronchospasm, itching and inflammation. At the point of contact, scars or spots (hyper-pigmentation of the skin) may remain even for a few years
  • Portuguese caravel (Physalia physalis), typical of the Atlantic Ocean, is now increasingly found also in the Mediterranean (for example off the coast of Sicily, Calabria and Sardinia) and is the most dangerous species.It is always found on the surface because in reality it is not a real jellyfish, but a colony of polyps attached to a floating chamber filled with air. In the presence of this jellyfish you should always get out of the water! Contact with P. physalis it usually causes severe pain and skin irritation, with redness and sores in the area of ​​the skin that comes into contact with the tentacles of the polyps. The pain usually subsides or stops after 1-2 hours, and the sores may fade after a few days. Systemic effects are rarely observed with abdominal pain, nausea, vomiting and spasms. It is important to note that even when beached, after several days of dehydration in the sun, polyps are still able to cause effects on the skin following contact.
  • Chrysaora hysoscella, a very irritating species, is frequent in spring but rarely gives rise to extensive blooms. The umbrella can reach 30 cm in diameter
  • the cubomeduse, so called for their physical form, they are particularly dangerous. Of the approximately 50 species of cubomedusa, also called sea wasps, only a few have venom that can be lethal to humans, and those are not found in the Mediterranean. The only Mediterranean species (Carybdea marsupialis) has an umbrella with a maximum diameter of 5 cm, it is however very irritating and frequent in summer and autumn. During the day, it swims along harbor and sandy bottoms, and rises to the surface at night to feed
  • Olindias phosphorica, it is another small (the umbrella reaches a maximum of 8 cm) and transparent jellyfish, horticultural but not very widespread, which is encountered in summer and autumn. It quickly rises to the surface and then slowly descends to the bottom, to catch the plankton it feeds on

What to do in case of contact

The treatment of ailments resulting from contact with a jellyfish generally aims at reducing pain, eliminating the nematocysts left on the skin, with a local treatment of the affected skin areas. It is suggested to:

  • stay calm, breathing normally; if a child has hit a jellyfish, it is good to reassure him. If you are close to the shore, get out of the water, otherwise call attention for help
  • to check, once out of the water, that no parts of the jellyfish remained attached (nematocysts), remove them if possible without touching them, for example with a spatula, a knife (not on the blade side) or a rigid plastic card (credit card type) by scraping the skin to carefully remove as much as possible
  • srinse the affected area with sea water, do not use fresh water because it would cause the nematocysts still intact to rupture and release more stinging liquid
  • after removing the jellyfish residues and rinsing the part, make cold compresses, which have an analgesic effect, however, preventing ice, made up of fresh water, from coming into contact with the skin
  • apply an astringent aluminum chloride gel, which serves to soothe itching and block the spread of toxins. It is found in pharmacies and is also used to soothe itching from mosquito bites
  • cover the affected area and do not expose it to the sun, because being sensitive to sunlight it tends to darken causing unsightly spots / scars

If complications arise such as widespread redness and / or swelling of the skin, difficulty breathing, sweating, paleness, headache, nausea, vomiting, dizziness, confusion, go to the emergency room or call 911, explaining what happened.

If you are able to recognize the jellyfish you have come into contact with, it is better to follow the following specific indications:

  • Physalia physalis, Portuguese caravel, make compresses of hot water (40-45 ° C) for 10-20 minutes
  • Charibdea marsupialis, the cubomedusa, you can use a little vinegar to neutralize any fragments of tentacles left on the body, before rinsing with sea water; make compresses of hot water (40-45 ° C) for 10-20 minutes
  • Olindias phosphorica, you can use a little vinegar to neutralize any jellyfish cells left on the body, before rinsing with sea water; proceed with cold water compresses

What NOT to do in case of contact

  • do not scratch, before removing the nematocysts, which could rupture, making the situation worse
  • do not touch the nematocysts (the parts of tentacles left on the skin) with your hands, to avoid transferring part of the stinging liquid to particularly sensitive areas such as eyes and mucous membranes
  • do not rinse the affected area with fresh water, it would cause the rupture of the nematocysts still intact and the release of other stinging liquid
  • do not rub the affected area with sand or a hot stone, even if the toxins are inactivated by heat, the temperature required to do so is over 50 ° C
  • do not use remedies such as ammonia or urine (containing ammonia) alcohol or vinegar (unless you know the species you are with got in touch) because they have no action on the stinging liquid of jellyfish and could further irritate the affected part (read the Hoax)
  • do not expose the affected area to the sun for a few days, or use total sunscreen creams, to avoid the formation of spots

Antihistamine creams or creams with a low cortisone content are of little use in the immediate term (they take effect after about 30 minutes, when in normal conditions, the disorders have already disappeared).


Prevention and proper management of bathing activities play an important role in minimizing contact with jellyfish.

  • inquire about the characteristics of the typical jellyfish of the area, in case of trips to exotic places, remembering that jellyfish are not all the same: what is valid on our coasts is not necessarily valid in different areas
  • pay attention to the presence of warning signs and signs positioned on the beach, and follow the instructions
  • avoid playing or bathing in the sea during the period when jellyfish invade its waters
  • also avoid touching the beached jellyfish, even if with exposure to the sun they dehydrate (more than 95% are made up of water), the stinging liquid often remains
  • in case of diving, wear a lycra suit, or equivalent, able to cover the whole body to protect itself
  • if you use protective nets for the bathing area, should be large enough to provide protection against the tentacles of small jellyfish

The application of a water-resistant sunscreen containing zinc oxide (a substance that mimics the mucous coating used by clownfish to inhibit the stings of sea anemone tentacles) may be beneficial for swimmers, as it has been shown that significantly reduces contact and the severity of ailments (symptoms).


Ministry of Health. Water Portal. Dangerous aquatic organisms

Higher Institute for Environmental Protection and Research (ISPRA). Project "Sea And ... stay healthy - Jellyfish in the Mediterranean Sea"

Encyclopedia Treccani. Jellyfish

In-depth link

Guide to the identification of jellyfish and other gelatinous organisms of the Mediterranean

Marevivo. Jellyfish

National Oceanic and Atmospheric Administration (NOAA). What are jellyfish made of? (English)

healthdirect. Jellyfish stings (English)

Wikimedia commons. Physalia physalis, Tayrona national park, Colombia (Image)

Wikimedia commons. Box jelly (Picture)

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