During a sting, bees, wasps, bumble bees and hornets inject venom into the skin. A normal local reaction to a sting is limited to the sting site and consists of pain, swelling, and redness. However, local reactions can also result in massive swelling of an entire extremity, and may last for several days. In such a case, these reactions are called large local reactions. Up to 25% of the general population may suffer from such large local sting reactions.

In up 3.5% of the population, stings may induce systemic anaphylactic reactions. A systemic reaction is not limited to the sting site. Within a few minutes, usually within half of an hour, general symptoms may occur, which may be limited to the skin (itching, redness, rash), or which may affect internal organs and induce cardiovascular symptoms (palpitation, low blood pressure), shortness of breath, abdominal cramps or loss of consciousness. Life-threatening reactions (anaphylactic shock) or even fatal reactions may occur. Elicitors of such systemic anaphylactic reactions are mainly stings from bees and wasps, rarely also from bumble bees or hornets.