Most jellyfish have tendrils or oral arms coated with thousands
of microscopic nematocysts. Generally, each nematocyst has a
"trigger" (cnidocil) paired with a capsule containing a coiled
stinging filament armed with exterior barbs. Upon contact, the
filament rapidly unwinds, launches into the target, and injects
toxins.
When stung by a jellyfish, first aid may be in order. Though most
stings are not deadly, some stings, such as those of the box
jellyfish (Chironex fleckeri), may be fatal. Serious stings may
cause anaphylaxis and may result in death. Hence, people stung by
jellyfish must get out of the water to avoid drowning. In serious
cases, advanced professional care must be sought. This care may
include administration of an antivenin and other supportive care
such as required to treat the symptoms of anaphylactic shock. The
most serious threat that humans face from jellyfish is the sting of
the Irukandji, which has the most potent and deadly venom of any
known species.
There are three goals of first aid for uncomplicated jellyfish
stings: prevent injury to rescuers, inactivate the nematocysts, and
remove any tentacles stuck on the patient. To prevent injury to
rescuers, barrier clothing should be worn. This protection may
include anything from panty hose to wet suits to full-body
sting-proof suits. Inactivating the nematocysts, or stinging cells,
prevents further injection of venom into the patient.
Vinegar (3 to 10% aqueous acetic acid) should be applied for box
jellyfish stings. Vinegar, however, is not recommended for
Portuguese Man o' War stings. In the case of stings on or around
the eyes, vinegar may be placed on a towel and dabbed around the
eyes, but not in them. Salt water may also be used in case vinegar
is not readily available. Fresh water should not be used if the
sting occurred in salt water, as a change in pH can cause the
release of additional venom. Rubbing the wound, or using alcohol,
spirits, ammonia, or urine will encourage the release of venom and
should be avoided.
Once deactivated, the stinging cells must be removed. This can be
accomplished by picking off tentacles left on the body. First aid
providers should be careful to use gloves or another readily
available barrier device to prevent personal injury, and to follow
standard universal precautions. After large pieces of the jellyfish
are removed, shaving cream may be applied to the area and a knife
edge, safety razor, or credit card may be used to take away any
remaining nematocysts.
Beyond initial first aid, antihistamines such as diphenhydramine
(Benadryl) may be used to control skin irritation (pruritus). To
remove the venom in the skin, apply a paste of baking soda and
water and apply a cloth covering on the sting. If possible, reapply
paste every 15-20 minutes. Ice can be applied to stop the spread of
venom until either of these is available.
Jellyfish will not purposely attack people. They catch fish and
other marine creatures by spreading their tentacles like fishing
lines. The tentacles of some species can inflict painful stings,
especially those of the lion's mane jellyfish.
