What does anaphylaxis mean?
Anaphylaxis is a noun referring to an acute, severe, and potentially life-threatening allergic reaction that affects the entire body. It occurs when the immune system overreacts to a normally harmless substance — most commonly certain foods (such as peanuts or shellfish), insect stings, or medications — releasing a flood of chemicals like histamine that can cause hives, swelling of the throat, difficulty breathing, vomiting, and a precipitous drop in blood pressure. Symptoms typically begin within minutes of exposure, making anaphylaxis a medical emergency requiring immediate treatment with an injection of adrenaline (epinephrine), often followed by hospital care. The word derives from Greek roots meaning 'excessive protection', a deliberate contrast with prophylaxis, which means protection against disease. Because it names a dramatic and widely discussed phenomenon — food-allergy warnings, school policies, and emergency preparedness all reference it — anaphylaxis is an important term in both medicine and public health discourse.
nounAn acute, potentially life-threatening allergic reaction that occurs rapidly after exposure to an allergen, involving widespread release of histamine and other mediators and typically causing symptoms such as hives, swelling, airway constriction, and a dangerous drop in blood pressure.
- A rapid, severe, whole-body allergic reaction to an allergen (such as food, insect venom, or medication) that can be fatal without prompt treatment with adrenaline.
"After eating a single cashew, she went into anaphylaxis and was rushed to the emergency room for an adrenaline injection."
"Peanut allergies are among the most common triggers of anaphylaxis in children."
"The hospital keeps adrenaline auto-injectors on hand because anaphylaxis can develop within minutes of a bee sting."
The plural follows standard English -is → -es alternation (as with 'analyses'). It is rarely needed, since the word usually refers to a single episode; clinicians more often speak of recurrent episodes than use the plural form.
"Patients who have experienced repeated anaphylaxes are advised to carry multiple auto-injectors."
The word 'anaphylaxis' was coined by scientists who were trying to create immunity in dogs — and accidentally discovered its deadly opposite instead.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of anaphylaxis
The term anaphylaxis was coined at the turn of the twentieth century by French physiologists Charles Richet and Paul Portier, who observed that dogs previously exposed to sea anemone toxin reacted fatally to a later dose — the opposite of the protective immunity they had expected. They built the word from Greek roots: 'ana-' meaning 'backward' or 'against', combined with 'phylaxis', meaning 'guarding' or 'protection', so the term literally signifies 'without protection'. Richet received the Nobel Prize in Physiology or Medicine in 1913 partly for this work. The same Greek root gives us prophylaxis, meaning preventive protection, making the two words deliberate opposites.
Word family
Usage notes
Anaphylaxis is a formal, medical term used in clinical settings, health education, and news reporting; it is not part of casual everyday speech. It always carries serious connotations, as it describes a medical emergency. The related adjective 'anaphylactic' is common in phrases such as 'anaphylactic shock' and 'anaphylactic reaction'.
Don't confuse with
Anaphora is a rhetorical or linguistic term for repetition of a word or phrase at the beginning of successive clauses, whereas anaphylaxis is a severe allergic reaction.
Prophylaxis refers to preventive treatment taken to ward off disease, while anaphylaxis is an acute, harmful allergic reaction — they share a Greek root but are near-opposites in meaning.