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It’s normal for an insect sting to cause a mild local reaction. This is not a sign of allergy and is not serious. It’s important to be able to tell the difference between a normal reaction and an allergic reaction. Any severe reaction, of course, requires medical attention.
Insect sting reactions can be classified as toxic or allergic, immediate or delayed, and local, large local, or systemic.
The "normal" reaction to an insect sting is an immediate local reaction. That means it happens within minutes or hours of the sting and affects only the area where the sting occurred. This is not an allergic reaction.
The symptoms of this type of reaction include:
A large local reaction involves redness and swelling over a large area surrounding the site of the sting. For example, if you are stung on your foot, your entire leg may swell. You may also experience fatigue, mild nausea, and low fever. These symptoms may be alarming but usually resolve within 10 days without treatment. A large local reaction is a type of allergic/hypersensitivity reaction. Although a large local reaction is normally self-limiting, people who have previously experienced such a reaction have a 5 to 10 percent risk of a systemic allergic reaction upon future stings. You will want to discuss these symptoms with your doctor.
A reaction is considered delayed if it begins more than four hours after the sting. Rarely, symptoms appear a week after the sting. These may produce the syndrome of serum sickness. This is a systemic immune reaction.
The symptoms may include:
You should call your doctor if you have these symptoms.
Anaphylaxis is a severe, systemic allergic reaction and a medical emergency. This reaction usually starts within minutes of the sting, though it may start as much as an hour later.
The symptoms include:
Anaphylaxis requires immediate medical attention. Give an epinephrine injection and antihistamines if available. Call 911. If not treated promptly, anaphylaxis can be fatal.
If you are stung by a poisonous insect, you may have a toxic reaction. This is not allergy but rather the effect of the poison in the insect’s venom. The severity of the reaction depends on the toxicity of the venom, the amount of venom injected, and your tolerance for the venom. Symptoms include:
A toxic reaction can be life threatening. You should call 911 for immediate medical assistance.
Written by: the Healthline Editorial Staff
Medically reviewed on: Sep 08, 2014: Kenneth R. Hirsch, MD
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