What should you know about slow reacting substance of anaphylaxis?

The older term describes a group of substances released by immune cells after an allergen triggers the body. Leukotrienes are among the chemicals involved. They act more slowly than histamine and may keep airway muscles tightened, increase mucus, and contribute to swelling in the throat or lungs. This can lead to wheezing, cough, chest tightness, hoarseness, or difficulty breathing. The chemical process is part of anaphylaxis; it is not a separate diagnosis.

Food can trigger anaphylaxis, but medicines, insect stings, latex, and other allergens can also be responsible. Symptoms may involve the skin, breathing, circulation, or digestion, and they can progress quickly.

If anaphylaxis is suspected, use the person’s prescribed adrenaline auto-injector immediately, if available, and call emergency services. Follow the device instructions and use a second injector if the emergency plan advises it. Lay the person down with legs raised unless breathing is easier sitting up; do not let them stand or walk. Even if symptoms improve, urgent medical assessment is needed because symptoms can return. Learn more about [Anaphylaxis Emergency Treatment](/treatments/acute-and-urgent-care/anaphylaxis-emergency-treatment/) and [Anaphylaxis](/conditions/anaphylaxis/).

Call emergency services for sudden breathing difficulty, wheezing, throat or tongue swelling, faintness, confusion, collapse, or widespread symptoms after possible allergen exposure. Do not wait to see whether an antihistamine works; it does not replace adrenaline for airway or circulation problems. A clinician can review suspected triggers and arrange [Allergy Testing](/treatments/diagnostics-and-screening/allergy-testing/).

Ask which symptoms should prompt adrenaline, whether you need an emergency action plan, how to check and use your injector, and whether [Food Allergy](/conditions/food-allergy/) or another trigger needs assessment. Mention any episodes of [Wheezing](/symptoms/wheezing/) or delayed symptoms after exposure.