A systemic allergic reaction is a potentially fatal allergic reaction that is most often triggered by food, medications and insect bites, with symptoms appearing within a very short period of time. Such allergic reactions are often unpredictable, and some people who experience them know what triggers their allergy and have had one or more episodes, while others may suddenly have a severe allergic reaction without even knowing they have an allergy. I. Common symptoms of a systemic allergic reaction Symptoms of a systemic allergic reaction usually appear within minutes to an hour after exposure to the allergen. The most common symptoms are hives and angioedema (e.g., swelling of the skin of the mouth, lips, and eyes), and about 80 to 90 percent of patients will have skin symptoms. Respiratory symptoms occur in 70% of patients, especially in those who also have asthma or other chronic respiratory disease. Dizziness, blurred vision or loss of consciousness due to decreased blood pressure will occur in 70% of patients. The following are the symptoms that commonly occur in various organs during a systemic allergic reaction: Skin: itching, large flushing, urticaria (hives), localized skin swelling (angioedema) Eyes: itchy, watery eyes, red, bloodshot eyes, swollen skin around the eyes Nose and mouth: sneezing, runny nose, nasal congestion, hard or swollen tongue, metallic taste in the mouth Lungs and throat: inspiratory or expiratory effort, recurrent coughing, chest tightness Heart and circulation: dizziness, weakness, fainting, fast or slow heartbeat or irregular heartbeat, lower blood pressure Digestive system: nausea, vomiting, abdominal cramps, diarrhea Nervous system: anxiety, unresponsiveness or near-death feeling II. Sometimes the causes of allergic reactions may be obvious, sometimes it is difficult to identify. Food: In children, eggs, milk, peanuts, nuts, fish, wheat and soy are the most common food triggers. In adolescents and adults, peanuts, nuts, fish, and crustaceans (shellfish such as shrimp) are the most common triggers. Any food, including fruits, vegetables, plant seeds and some spices and food additives, can cause an allergic reaction. Medications: such as antibiotics (penicillin and cephalosporins) and antipyretics and analgesics (aspirin, ibuprofen). Insect venom: including bees, wasps and fire ants. Latex from natural rubber: present in some latex gloves, balloons, condoms, sports equipment and medical supplies. Allergen immunotherapy (desensitization): used to treat allergic rhinitis (hay fever) and asthma. Exercise or exercise after ingesting certain foods (such as wheat, celery, shrimp or other foods) or medications (such as aspirin, ibuprofen); this is called exercise-induced systemic allergic reaction or food-dependent exercise-induced systemic allergic reaction. Less common triggers include airborne allergens (e.g., horse dander), human semen, cold water, or cold air. Risk factors for systemic allergic reactions Some people are more likely than others to have an allergic reaction or to develop severe symptoms after an allergic reaction has occurred: Previous severe allergic reactions: People who have had an allergic reaction to a specific substance in the past are at increased risk of having another allergic reaction. However, the severity of previous allergic reactions does not predict the severity of future reactions, and even people who have had mild reactions in the past may have severe allergic reactions in the future. Asthma and other chronic lung diseases: People with asthma or other chronic lung diseases are more likely to have severe respiratory symptoms during an allergic reaction. Other diseases: People with cardiovascular disease and coronary artery disease are also at higher risk of severe allergic reactions. IV. What should I do if I have a sudden systemic allergic reaction? If you have ever had a generalized allergic reaction, you should try to find and determine the cause of the allergic reaction with the help of an allergist. However, sometimes the cause of an allergic reaction is difficult to find, and due to the unpredictability of allergic reactions, sometimes the symptoms may be mild and subside on their own, and sometimes they may be severe, with severe respiratory and cardiovascular symptoms within a few minutes to an hour, or even life-threatening. Therefore, it is necessary to develop an “emergency action plan” for systemic allergic reactions. The most important part of this emergency action plan is to carry an epinephrine auto-injector with you and to know when to use it and how to use it. Emergency Action Plan Step 1: Immediately call the emergency number. Emergency Action Plan Step 2: Immediately self-medicate with an epinephrine auto-injector (also called an epinephrine pen). Epinephrine is the best drug of choice to treat allergic reactions and is most effective when given immediately before symptoms become severe. Antihistamines used to relieve hives and itching or asthma inhalation medications to relieve wheezing symptoms are not sufficiently effective to control the symptoms of an allergic reaction. Emergency Action Plan Step 3: Remove the trigger, such as stopping the consumption of suspect foods and removing any residual insect stings from the skin. Emergency action plan step 4: Visit a hospital emergency room. Some patients whose symptoms do not completely resolve after one epinephrine injection need to continue monitoring and treatment in the hospital. V. How to use an epinephrine pen An epinephrine auto-injector (also called an epinephrine pen) is a pre-filled syringe in which 0.3 mg of epinephrine (0.15 mg for children) is pre-filled and is easy to use by patients or other lay people. Currently, EpiPen® from the US and Jext® from the UK are more commonly used abroad. Jext® Epinephrine Pen is registered in Hong Kong and is therefore available at certain designated pharmacies in Hong Kong. The Chinese epinephrine pen (anaphylaxis resuscitation kit), which integrates the epinephrine injection (1mg/1ml/stem), abrasive wheel, syringe and sterile cotton pad used in hospitals into a portable medication box, has the disadvantage that it is more cumbersome to use than an auto-injector and requires repeated training to ensure that 0.3-0.5ml of medication can be extracted smoothly for injection in the event of an allergic reaction. For patients who have had systemic allergic reactions, it is recommended to carry at least one epi-pen per day, and some experts recommend carrying two, as one medication often does not provide relief for some patients with severe allergic reactions. Six. So when do I need to use an epinephrine pen? For a person who has had a previous allergic reaction, the injection is needed immediately if he/she experiences the following symptoms: difficulty breathing: feels tightness in the throat: feels dizzy or near death. In case of an allergic reaction in a child, the epinephrine pen should be administered immediately in the following cases: unresponsive or non-responsive to calls from other people during an allergic reaction, history of food allergy, recurrent vomiting shortly after eating a food accompanied by flushing of the skin or hives, recurrent coughing during an allergic reaction. Previous systemic allergic reactions, widespread urticaria after consuming a food to which you are suspected to be allergic, previous definite food-induced severe allergic reactions, inadvertent ingestion of an allergic food, and the use of an auto-injector before the onset of symptoms.