Symptoms from jellyfish or Portuguese man-of-war stings may develop right away or be delayed for several hours or days.

The pain from jellyfish or Portuguese man-of-war stings may be intense and may last for several hours. Itching at the site is common and may last for a week. The skin at the site of the stings may have a line of red, brown, or purplish raised bumps that may last for 1 to 2 weeks. Blisters and deep sores (ulcers) may develop. Healing is generally a slow process that may take many weeks. Permanent scars may occur at the site of a sting.

Small children are at risk for stings in the mouth if they put a jellyfish or portion of a tentacle in their mouths. A sting to the mouth or throat can cause sudden and severe swelling, which can be life-threatening.

A severe allergic reaction (anaphylaxis) is rare and would need emergency medical care right away.

The reaction that you have to a jellyfish or Portuguese man-of-war sting depends on many things. The strength of the venom changes with the type of jellyfish and the time of the year. Other things that affect the severity of your reaction include:

• Your size, age, and general health.
• The location of the sting and how much of your body was stung.
• The size or number of jellyfish or tentacles that stung you.