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Why is my wasp sting swollen and hot?

If you’ve been stung by a wasp, it’s common to experience swelling, redness, pain, and heat at the site of the sting. This inflammatory reaction is the result of your body’s natural response to the toxins in the wasp’s venom. While uncomfortable, it’s generally not cause for alarm and will usually resolve on its own within a few days. However, in some cases, a more severe reaction can occur.

What causes the swelling and heat from a wasp sting?

When a wasp stings, it injects a tiny amount of venom through its stinger into your skin. This venom contains several chemicals including:

  • Histamine – Causes swelling due to increased blood flow and fluid leakage from blood vessels
  • Acetylcholine – Leads to increased pain and inflammation
  • serotonin – Induces pain and itching sensations
  • Melittin – Breaks down cell membranes and damages tissues
  • Wasp kinins – Increase swelling and cause pain

These chemicals trigger an immediate immune reaction at the site of the sting characterized by:

  • Swelling – Due to increased blood flow and fluid accumulation
  • Redness – From enlarged blood vessels dilating near the surface of the skin
  • Heat – Caused by increased blood flow and inflammatory chemicals
  • Pain – From the direct irritation and inflammation of tissues

This combination of swelling, redness, warmth, and pain following a wasp sting is known as a local reaction. It’s the normal response of your body’s immune system to isolate and neutralize the toxins.

What determines the severity of the reaction?

Several factors contribute to the severity of swelling and inflammation from a wasp sting including:

  • Number of stings – Getting stung multiple times can worsen the reaction
  • Location of sting – More sensitive areas like the face or neck tend to react more
  • Toxin dose – Amount of venom injected from larger species of wasps
  • Allergic status – Those with wasp venom allergies react more severely
  • Previous stings – Increased sensitivity may develop after repeated stings

Additionally, the natural variation in immune response from person to person can influence the degree of swelling and inflammation. Those with more reactive immune systems tend to develop more pronounced reactions.

When is swelling and heat normal after a wasp sting?

It’s very common for a wasp sting to cause localized swelling up to several inches across, redness, warmth, and throbbing pain within the first 24 hours. This represents a typical immune reaction and doesn’t necessarily indicate a serious problem or allergy.

Here are some general guidelines on normal swelling and heat following a wasp sting:

  • Swelling less than 3 inches (7.5 cm) across – Very common and not worrisome as long as confined to sting site
  • Mild-to-moderate redness – Also very common and expected
  • Warmth around the sting – Result of increased blood flow to the area
  • Tenderness, itching, throbbing – Annoying but normal sensations
  • Symptoms peak within 48 hours – Inflammation shouldn’t worsen after this time

As long as the swelling, redness, and heat remain localized around the sting site and start improving within a couple days, it can be considered a normal reaction. Using ice and over-the-counter pain medications can help manage discomfort during this time.

When to seek medical care

In some cases, swelling and inflammation from a wasp sting can become more serious or signal an allergic reaction. Seek prompt medical care if you experience:

  • Swelling spreading beyond the sting site
  • Swelling lasting more than 3-5 days without improvement
  • Increasing pain or swelling
  • Dizziness, fainting, trouble breathing
  • Hives, itchy rash, or swelling in areas beyond the sting
  • Nausea, vomiting or abdominal pain
  • Red streaking from the sting site

These signs may indicate a whole-body allergic reaction, infection, or other complication requiring medical treatment. People with a known allergy to wasp stings should seek immediate care after being stung.

How to treat swelling and heat from a wasp sting

For routine swelling, redness, and warmth around a wasp sting, these self-care measures can help ease discomfort:

  • Wash the sting area with soap and water to remove any remaining venom
  • Apply a cold compress or ice pack wrapped in cloth for 10-20 minutes several times a day
  • Keep the area elevated above the level of your heart when possible
  • Take over-the-counter pain medication like acetaminophen or ibuprofen
  • Avoid scratching or picking at the sting site to prevent infection
  • Use calamine lotion and oral antihistamines to relieve itching
  • Consider applying hydrocortisone cream to lessen inflammation

Within 3-5 days, the swelling, pain, and heat should gradually dissipate. See your doctor if your symptoms are worsening or haven’t improved after about a week.

How to prevent complications and severe reactions

You can take these measures to avoid complications and more serious reactions to wasp stings:

  • Have epinephrine auto-injectors on hand if you have a known wasp venom allergy
  • Avoid areas where wasps are active like nests, food, and garbage
  • Wear protective clothing like long sleeves and pants outdoors
  • Avoid swatting at wasps and stay calm if one approaches
  • Speak to your doctor about allergy testing if you’ve had severe reactions before
  • Monitor the sting site for signs of infection like pus, increasing redness, or streaking redness
  • Call 911 immediately if you experience any difficulty breathing, dizziness, or swelling of the throat

Being aware of the signs of allergic reaction and treating even minor stings appropriately can help prevent complications and more involved swelling reactions.

When to seek emergency care

Anaphylaxis is a potentially life-threatening allergic reaction that can occur with insect stings. Seek emergency care immediately if you experience any of the following signs after a wasp sting:

  • Difficulty breathing, wheezing
  • Swelling of the lips, tongue, throat
  • Dizziness, confusion, fainting
  • Nausea, vomiting, diarrhea
  • Skin reactions like hives, itching, swelling
  • Heart palpitations, racing pulse
  • Loss of consciousness

Anaphylaxis is a medical emergency that requires epinephrine and emergency medical treatment. Call 911 or emergency services right away if you develop any concerning symptoms after being stung by a wasp.


Swelling, redness, pain, and warmth around a wasp sting are common and represent a normal reaction as your body fights off the venom. However, multiple stings or allergic sensitivity can result in more severe swelling and consequences. Seek prompt medical attention if swelling spreads, gets worse after 2-3 days, or is accompanied by worrisome symptoms like trouble breathing. With proper first-aid and awareness of possible complications, most routine wasp stings can be managed safely at home.