Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Emergency care is needed for breathing difficulty, throat or tongue swelling, collapse, confusion, a rapidly worsening reaction, or symptoms involving several body systems.
Multiple stings may also require emergency assessment.
Contact a clinician promptly for possible infection, especially if there is fever, pus, increasing tenderness, or red streaking.
A sting to the eye, inside the mouth, or near the throat also needs prompt assessment.
Routine follow-up is usually unnecessary when mild pain and swelling steadily improve.
Seek medical advice if local symptoms are severe, continue to worsen, interfere with movement, or do not begin resolving as expected.
After any reaction involving widespread hives, breathing symptoms, dizziness, fainting, or symptoms away from the sting site, arrange follow-up with a clinician or allergist.
This visit may include allergy testing, an epinephrine prescription, training on auto-injector use, and discussion of venom immunotherapy.
The article also says
People prescribed epinephrine should check expiration dates, store the device as directed, carry it as advised, and make sure family members or close contacts know where it is and how to use it.
Every sign above is quoted from the sofidex article on Bee, wasp, hornet, or yellow jacket sting. If you are not sure, err upward — it is always reasonable to be checked.