Reactions to box jellyfish stings can be immediate or delayed by several days or even weeks. Complications may include the following.
Some box jellyfish stings cause Irukandji syndrome, a group of symptoms that begin 20–30 minutes after the sting and progress over a few days.
- Muscle cramping and spasms
- Nausea and vomiting
- Rapid heart rate
- High blood pressure
In very serious cases, a person may experience cardiogenic shock or a pulmonary edema.
Irukandji syndrome often requires hospitalization, so if you have been stung by a jellyfish, pay close attention to symptoms that may arise sometime afterward.