Anaphylaxis

Anaphylaxis is a severe, potentially fatal allergic reaction that progresses very rapidly. It is a systemic event, meaning it affects many different parts of the body at once. This reaction can lead to life-threatening situations if it is not treated immediately. It typically involves more than one body system, such as the skin and the respiratory system. Symptoms usually begin within minutes to hours after exposure to a trigger.

Because it can escalate so quickly, urgent medical care is always required. Even if a person uses an epinephrine autoinjector, they must still see a doctor.

The biological mechanism of anaphylaxis involves a rapid cascade of chemical releases. The process is primarily driven by certain white blood cells called mast cells and basophils. In most cases, the reaction is immunologic, meaning it is triggered by immunoglobulin E, or IgE. When an allergen enters the body, it binds to these IgE antibodies. This binding activates specific receptors on the surface of the mast cells and basophils. Once activated, these cells release inflammatory mediators, such as histamine, into the body.

These chemicals cause blood vessels to leak fluid and cause smooth muscles in the airways to contract. This can lead to swelling and a dangerous drop in blood pressure.

There are two main ways this reaction is triggered in the body. The first is the immunologic mechanism described above, where IgE antibodies recognize a specific antigen. The second is a non-immunologic mechanism. In these cases, substances trigger the mast cells directly without using IgE. Examples of non-immunologic triggers include certain medications, contrast media, or even changes in temperature. Some people experience a mixed type of anaphylaxis that includes both types of features. This can occur during certain medical treatments, such as some types of chemotherapy.

Triggers for anaphylaxis are incredibly diverse and vary by age and culture. For children and young adults, food is the most common trigger. Common foods include peanuts, milk, eggs, fish, wheat, and shellfish. In Western cultures, these are very prevalent, while in Asia, rice and chickpeas are frequent sources. In older adults, insect stings and medications are more common causes. Insect venom from bees, wasps, or ants can trigger a reaction in susceptible people. Medications like penicillin or non-steroidal anti-inflammatory drugs (NSAIDs) are also frequent culprits.

Some people even experience reactions due to physical exercise or extreme temperatures.

Anaphylaxis affects different body systems in predictable patterns. The skin is the most commonly affected area, appearing in 80% to 90% of cases. This often shows up as hives, itching, or swelling known as angioedema. Respiratory issues, such as shortness of breath or wheezing, affect about 70% of people. Gastrointestinal symptoms, including vomiting and abdominal pain, occur in 30% to 45% of cases. Cardiovascular effects, such as low blood pressure or a fast heart rate, affect 10% to 45% of patients. Finally, the central nervous system is involved in 10% to 15% of cases, sometimes causing confusion or anxiety.

Medical professionals diagnose anaphylaxis based on presenting symptoms after exposure to a trigger. The primary and most important treatment is the injection of epinephrine into a muscle. Epinephrine helps to reverse the symptoms by acting on the body's systems.

Doctors may also provide intravenous fluids to help stabilize blood pressure. It is also helpful to place the person in a reclining position with their feet elevated. This position helps to restore normal blood flow to the body. While antihistamines and steroids are sometimes used, they are considered complementary to epinephrine. People with a history of these reactions are advised to carry an epinephrine autoinjector.

Globally, the impact of anaphylaxis is significant and widely studied. It is estimated that between 0.05% and 2% of the world's population will experience it at some point. The condition occurs most frequently in females and young people. Despite the seriousness of the reaction, survival rates are high in certain settings. In the United States, approximately 99.7% of people hospitalized with anaphylaxis survive. Researchers have noted that as reporting became more accurate in the 2010s, the recorded rate appeared to increase. Understanding these patterns helps doctors better prepare for and treat these rapid emergencies.