Rhizostoma pulmo is a widely distributed scyphozoan in the Mediterranean Sea. Their stings result mainly in erythema, small vesicles, or/and pain, and cause a high number of bathers to seek assistance from first-aid services during the summer season. Despite the threat that jellyfish stings represent to public health, there is disagreement in the scientific community on first-aid protocols, with the dispute largely centered around the effectiveness of vinegar. In the present research, we investigated the effect of commonly used rinse solutions on nematocyst discharge in R. pulmo and the effect of vinegar on three more scyphozoans (Aurelia sp., Cassiopea sp., and Rhizostoma luteum). Scented ammonia, vinegar, and acetic acid triggered nematocyst discharge in R. pulmo. Vinegar also caused nematocyst discharge in Aurelia sp., Cassiopea sp., and R. luteum. In contrast, seawater, baking soda, freshwater, urine, and hydrogen peroxide were considered neutral solutions that did not induce nematocyst discharge. These results indicate that the use of vinegar, acetic acid, or commercial products based on these compounds is counterproductive. Their use can worsen pain and discomfort caused not only by R. pulmo stings but also by those of any scyphozoan. The use of seawater is recommended for cleaning the R. pulmo sting site until an inhibitor solution that irreversibly prevents nematocyst discharge is discovered.
Keywords: Scyphozoa class; cnidarian; cnidocyst; cnidocyte; first-aid protocol; nematocyst discharge; pain; venom.