Infected wasp sting — what to do?
By Wespenprofis.ch · Reviewed by:Fachbewilligung Schädlingsbekämpfung VFB-S · Updated: 3 July 2026
At a glance
A normal reaction to a wasp sting subsides within a few days. If redness or swelling instead keeps increasing after several days, if pus forms, if a fever develops or if a red streak runs away from the puncture site, this points to a bacterial infection — in that case, seek medical advice promptly.
This article is not a substitute for medical advice. If you experience difficulty breathing or swelling around the throat, call 144 immediately.
A certain amount of redness and swelling is part of every wasp sting. Sometimes, however, an additional bacterial infection develops. This article shows how to tell the two apart. It is not a substitute for medical advice.
Normal reaction versus infection
A normal sting reaction usually peaks within the first one to two days and then subsides steadily. With an infection, the opposite happens: redness, swelling and pain continue to increase even after two to three days instead of receding. Bacteria often enter the open wound through scratching, unclean hands or objects and trigger an infection.
Signs of an infection
- Redness that increases rather than decreases after the first few days
- Marked warmth and tenderness at the site
- Pus or weeping
- A red streak running from the puncture site towards the body (a possible sign of inflammation of the lymphatic vessels)
- Fever or a general feeling of illness
What you can do — and when to see a doctor
As long as there are no signs of infection, cooling still helps; you will find more on this in the guide “treating a wasp sting”. If the signs listed above do appear, however — in particular a red streak, fever or pus — you should see a doctor promptly. A bacterial infection may require treatment, for example an antiseptic or antibiotic measure, that only a doctor can assess. In any case, never pierce or squeeze the site yourself.
Distinguishing it from an allergic reaction
A larger swelling on its own is not necessarily a sign of an infection or an allergy: both reactions can look similar, but they differ in how they develop over time. An allergic reaction usually sets in within minutes of the sting, whereas an infection typically appears only after one to two days. There is more on assessing this in the article “wasp sting swelling”. If shortness of breath, hives across the whole body or dizziness also occur, call the emergency number 144 immediately. Basic first-aid measures after a sting can be found in the pillar guide “wasp sting — what to do?”.
Frequently asked questions
How do I know whether a wasp sting has become infected?
Warning signs are redness that increases rather than fades after two to three days, warmth to the touch, pus, fever or a red streak running from the sting site towards the body. This points to a bacterial infection.
Why does a sting become infected in the first place?
Bacteria usually enter the open puncture site through scratching or unclean hands. A bee sting that remains lodged in the skin and is not removed cleanly can also encourage an infection.
Is cooling still enough if the sting is infected?
Cooling continues to ease swelling and pain, but it does not treat the underlying bacterial infection. If there are signs of an infection, a doctor should assess the site.