Allergens from Insect Stings Insect stings may result in mild to severe allergic reactions.   When insects sting, they inject some chemicals into the victim and may cause allergic reactions. Insects whose stings / bits may lead to life-threatening allergic reactions include bees, wasps, hornets, yellow jackets, and fire ants.   In other milder cases, sensitivity is resulted from the salivary secretions of biting insects (such as mosquitoes, flies, lice and fleas) or the irritating substances left on the skin by some crawling insects.   Local allergic reactions involve swelling at the site of the sting, accompanied by severe itching and sometimes a few hives near the sting. Any amount of swelling, even if it involves the entire limb, is considered local if it is continuous with the sting area and if not in other parts of the body.   Systemic allergic reactions are those which affect any parts of the body, in addition to the portion that is stung. The symptoms of a moderate systemic allergic reaction involve at least two of the following:   Edema (swelling) of areas distant from the sting site   Sneezing   Chest constriction   Abdominal pain   Dizziness and nausea   A severe systemic reaction may be recognized by the above symptoms plus two of the following:   Difficulty in swallowing   Laboured breathing   Hoarseness and thickened speech   Weakness   Confusion   Feelings of impending disaster   Onset of allergic reactions The onset of allergic reactions can be immediate or delayed. In most cases, the shorter the time between the sting and the start of symptoms, the more severe the reaction will probably be. Most systemic allergic reactions begin 10 to 20 minutes after the sting. A delayed reaction, occurring several hours to 2 weeks after a sting, is similar to a drug reaction known as serum sickness. In this situation, the patient would experience painful joints, fever, hives or other skin rashes, and swollen lymph glands may develop.   Anaphylaxis The most serious reaction to a sting is closing of the airways or anaphylactic shock, in which the patient suffers not only from the above symptoms but also turns blue or shows evidence of a drop in blood pressure, collapse, or unconsciousness. These reactions may develop within minutes or hours after a sting, and the patient may die if treatment is not given promptly. (more info on anaphylactic shock)