A wasp sting that’s getting worse after five days, rather than better, is the clearest signal of infection. Normal sting symptoms and infection symptoms look almost identical in the first few days: redness, swelling, warmth, and pain. The key difference is timing. A normal venom reaction peaks within the first 48 hours and then steadily improves over 5 to 10 days. An infection sets in around that same 5-to-10-day mark, which is exactly why it’s so easy to confuse the two.
What a Normal Sting Looks Like
Right after a wasp sting, you’ll feel a sharp, burning pain. Within minutes, a small red welt forms at the site with minor swelling and itching. This is your body reacting to the venom, not to bacteria, and it typically fades within a few hours to a couple of days.
About 10% of people develop what’s called a large local reaction. The swelling can spread up to 4 inches beyond the sting site, and the area looks alarmingly red and puffy. These reactions usually start 6 to 12 hours after the sting, get worse over the next day or two, and then gradually resolve over 5 to 10 days. A large local reaction can look serious, but it’s still a venom response, not an infection. The hallmark is that it peaks and then improves on a predictable schedule.
Signs the Sting Is Infected
Infection from a wasp sting is uncommon, but it does happen. Bacteria enter through the puncture wound, especially if you scratch or rub the area and push microbes from your skin’s surface into the opening. The resulting infection is usually cellulitis, a bacterial skin infection that spreads through the tissue around the sting.
Here’s what to watch for:
- Worsening after day five. A normal sting should be noticeably better by this point. If redness, swelling, or pain are increasing instead of decreasing, that pattern flip is the single most reliable indicator of infection.
- Expanding redness. The red area around the sting keeps growing rather than shrinking. With cellulitis, the redness spreads outward from the original site and doesn’t stay contained.
- Increasing warmth. Some warmth at the sting site is normal early on. Warmth that intensifies days later, or skin that feels noticeably hotter than the surrounding area after the first few days, points toward infection.
- Pus or cloudy fluid. Any discharge draining from the sting site is not part of a normal venom reaction. Clear fluid from a blister can be normal, but pus or milky fluid is a sign of bacterial activity.
- Fever or chills. A normal sting doesn’t cause a fever. If you develop one alongside a worsening sting site, the infection may be spreading beyond the skin.
- Skin dimpling or blistering. The skin around the sting may develop a pitted, dimpled texture or new blisters that weren’t there in the first couple of days.
Red Streaks Are a Serious Warning
If you notice red streaks extending away from the sting site toward your armpit or groin, that’s a sign the infection has reached your lymph vessels. This condition, called lymphangitis, means bacteria are moving through your lymphatic system and can potentially enter your bloodstream. The streaks may be faint or obvious, and you might feel a throbbing pain along their path. This needs prompt medical attention because it can become life-threatening if bacteria spread further.
Infection vs. Allergic Reaction
Timing is the easiest way to tell these apart. An allergic reaction happens fast, usually within minutes to hours of the sting. An infection develops slowly, showing up days later. Their symptoms also differ in important ways.
An allergic reaction tends to cause itching and hives that spread well beyond the sting site, sometimes across your whole body. You might notice facial swelling, difficulty breathing, wheezing, or stomach pain. These are signs of anaphylaxis and require emergency treatment immediately.
An infection stays more localized, at least initially. It centers on the sting site and the surrounding skin, producing pain, warmth, and swelling that worsen gradually over days. You won’t get full-body hives from an infection, and you won’t get pus from an allergic reaction. If you’re unsure which you’re dealing with, the timeline tells the story: hours after the sting points to allergy, days after the sting points to infection.
Why the Confusion Happens
The tricky part is that the 5-to-10-day window where infection starts overlaps with the tail end of a normal large local reaction. Both involve redness, swelling, and warmth. The difference is direction: a normal reaction is winding down during this period, while an infection is ramping up. This is why it helps to track your symptoms over time rather than evaluating them at a single moment. If you notice the sting looked better on day four but worse on day six, that reversal is meaningful.
Drawing a line around the edge of the redness with a pen can help you track whether it’s expanding or shrinking. If the redness moves past your mark within a day, the area is still spreading, which is not typical of a healing sting.
How to Reduce Your Infection Risk
The biggest thing you can do is keep your hands off the sting. Scratching feels irresistible when a sting itches, but it drags bacteria from your skin’s surface into the wound. Wash the area gently with soap and water, apply a cold pack to reduce swelling, and leave it alone as much as possible.
Keep the site clean and dry over the following days. Covering it with a simple bandage can help if you’re prone to scratching, especially at night. If you notice any of the infection signs listed above, particularly after day five, or if you develop red streaks or a fever at any point, that’s your signal to get it evaluated by a healthcare provider. Bacterial skin infections from stings are treated with antibiotics, and they respond well when caught early.