Symptoms

Symptoms of an allergic reaction to insect stings vary from mild to life-threatening. The severity of your allergic reaction depends on your sensitivity to the allergens in the venom—not necessarily on the number of stings or how often you have been stung in the past.

Normal reaction to insect stings

It is normal to have some immediate swelling, redness, pain, and itching at the site of an insect sting—poisons and other toxins from the insect's venom enter the skin when you are stung. Normal symptoms from insect stings may last from a few hours to a few days, don't spread beyond the area of the bite, and include:

• Pain.
• Redness.
• Swelling.
• Itching.

Your normal reaction to fire ant stings will be slightly different. Fire ants sting numerous times in a cluster or ring, usually on a person's feet and legs because these are closest to the ground. The stings cause pain, redness, itching, and swelling at the site of the stings. Also, within several hours of being stung, small clear blisters appear and fill with fluid within 24 hours.¹

Large local allergic reactions

A large local reaction is when redness and swelling from an allergic reaction spread outward from the site of the sting. The reaction may affect only the area around the sting itself (such as your hand or forearm), or it may involve an entire limb or a broad area of the body. A large local reaction does not affect the entire body. It often will spread to cross the major joints on either side of the sting, such as the elbow and shoulder if stung on the upper arm. You may also experience a low fever, nausea, or fatigue. Symptoms usually occur within 12 to 24 hours after you are stung, peak within 48 hours, and go away within 5 to 10 days.^{2, 1}

People who have large local reactions to stings sometimes have a more severe local reaction each time they are stung. But for both children and adults, the risk of having a systemic (whole-body) reaction is relatively low, from 1% to 10%.²

Systemic reactions

Symptoms of a systemic allergic reaction develop in a different location than where you were stung and range from moderate to life-threatening. A severe systemic reaction is called anaphylaxis and requires immediate medical treatment.

Common systemic allergic reaction symptoms include:²

• Red, warm skin (flushing).
• Itching.
• Hives.
• Swelling in the deep layers of the skin (angioedema) or mucous membranes (such as the nose and throat). The swelling may occur in the lips, tongue, mouth, throat, ears, eyelids, palms, or soles of the feet.

Serious, life-threatening systemic allergic reaction (anaphylaxis) symptoms can include the symptoms above, as well as:¹

• Swelling and tightness in the throat or chest.
• Wheezing, coughing, and constriction or swelling in the throat that makes it difficult to breathe.
• Dizziness.
• Confusion, agitation, lightheadedness.
• Abdominal cramps, nausea, vomiting, or diarrhea.
• Abnormal heartbeat (arrhythmia).
• A drop in blood pressure.
• Shock that can lead to death.

Systemic reactions usually develop within 15 to 30 minutes or, occasionally, up to an hour after being stung. In some cases, anaphylaxis may continue or recur within 6 to 24 hours after being stung, and continued intensive treatment may be needed.²

If you had a previous systemic allergic reaction to a sting, you are at great risk of having a similar reaction if you are stung again.

Every systemic reaction to an insect sting should be considered a medical emergency. If you have a systemic allergic reaction, you should be observed in a clinic or emergency room afterwards to make sure you do not develop severe symptoms. If you have symptoms of a severe allergic reaction, seek immediate medical care by calling 911 or other emergency services.

You may also have another reaction to an insect sting that is not an allergic reaction (such as a toxic reaction or serum sickness).