Infected insect bites and stings
The vast majority of insect bites and stings heal spontaneously without problems. They may be intensely itchy and inflamed for a few days and require some symptomatic treatment.
Inflamed, often excoriated skin presents an opportunity for infection and a small number of insect bites or stings will become infected a few days after the initial injury. These require treatment to prevent the development of more serious infections (e.g. cellulitis, sepsis).
There is no need for prophylactic antibiotic treatment of insect bites and stings. Rapid-onset reactions to bites or stings are more likely to be allergic or inflammatory reactions rather than infection.