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The term anaphylaxis essentially means the opposite of "prophylaxis", a word used to describe the protection provided to the immune system through immunisation. Anaphylaxis can vary from a mild episode to a life-threatening allergic reaction. What differentiates anaphylaxis from other types of allergic reactions is that it is a sudden systemic condition that affects the entire body. If, for example, you received an insect sting but the swelling only occurred around the site of the sting then you are unlikely to experience anaphylaxis because the allergic reaction is localised. A systemic anaphylactic reaction can affect the respiratory tract, gastrointestinal tract, cardiovascular system and skin.

Anaphylaxis is relatively rare, with only approximately 30 people in every 100,000 being affected by it to varying degrees each year. Anaphylaxis can be a life-threatening complication but the annual death rate consists of only about one person in every two and a half million people. One problem concerning the nature of anaphylaxis is that some of its resulting fatalities may be mistakenly ascribed to other causes, while other conditions such as heart attacks, blood clots in the lungs, fainting, and panic attacks have correspondingly been mistaken for anaphylaxis.

Anaphylaxis affects the so-called "smooth" muscle tissue in the body that controls all the bodily functions that occur involuntarily. This includes the contraction of the gastrointestinal system and explains why abdominal cramps and vomiting can be a symptom of anaphylaxis. Anaphylaxis also causes vasodilation, dilating the walls of the blood vessels, and tachycardia, which increases the heart rate. The dilation of the blood vessels and capillaries cause a dangerous drop in blood pressure during anaphylactic shock. As fluid leaks from the blood stream into the tissues, the volume of blood is subsequently lowered.

As with other allergies, anaphylaxis results when the body's immune system overreacts to a substance in the body that is mistaken for a threat and this can be caused by a variety of allergens. Insect stings, foods like peanuts or shellfish, and medications such as penicillin can all be triggers. It is the antibody IgE (Immunoglobulin E) that sensitises the body to react this way in response to re-exposure to a particular allergen. For this to occur, you must first be sensitised to an allergen, even if you may be unaware that this process has occurred. The mast cells and basophils are coated by IgE and react chemically when the allergen is reintroduced into the body. Sometimes only a minute trace of the substance is required to provoke an allergic response.

Those with pre-existing asthma, eczema or allergic rhinitis (hayfever) may also have a relatively higher chance of experiencing anaphylaxis than those without these conditions. Some anaphylactic episodes are considered idiopathic and have been attributed to dysfunctional mast cells. Idiopathic anaphylaxis means that no specific cause could be discerned, although the patient may have an underlying allergy or asthma condition.

There is a different type of reaction called an anaphylactoid reaction that does not require the action of IgE, as prompted by prior sensitisation. Although it is not caused by IgE, the effects of an anaphylactoid reaction are the same as anaphylaxis. Anaphylactoid reactions are caused by direct stimulation of the mast cells and basophils and can occur during initial exposure to an allergen. A prior history of allergic conditions may mean that someone is relatively more susceptible to an anaphylactoid reaction than someone without these allergies. An anaphylactoid reaction can be caused by things as diverse as physical exertion, X-ray dye, and medications, including Aspirin or morphine.

The relative timeframe for anaphylaxis to occur after exposure to a particular allergen or antigen can vary from seconds to hours. It could take from 30 minutes to an hour before the problem develops. As a general rule, the sooner the symptoms of anaphylaxis appear after exposure then the more severe the reaction is likely to be. Those symptoms relating to the surface of the skin may be the first evidence of the reaction, including a tingling sensation or itchiness. During episodes of extreme anaphylactic shock, it is possible that cardiac arrest or unconsciousness could occur in less than ten minutes.

The actually severity of the reaction will vary from person to person. Some people experience relatively mild symptoms that only persist for a short duration. Others find that, after an initial improvement in their symptoms, they are prone to a delayed reaction, which causes a reoccurrence of the same symptoms hours later. This is called a "bi-phasic reaction". This only occurs in an estimated 10% of cases but it is important that caution is taken while this condition remains a possibility.

There are a diverse range of allergens that may be possible causes of anaphylaxis. Foods that have a higher incidence of causing anaphylaxis include peanuts, seafood, especially shellfish and fish, wheat, eggs, and milk. Some people are so sensitive to foods like peanuts or tree nuts like cashews, almonds, or walnuts that it takes only a trace of the allergen to cause a severe reaction. Insect stings are another type of common trigger, as is latex. Latex allergy is much more likely to be experienced by someone who had regular exposure to latex, such as healthcare workers. Certain medications, especially penicillin, hormone-based medications like insulin, and vaccines containing horse serum can also initiate IgE anaphylaxis. Another form of anaphylaxis is referred to as "exercise-induced food-dependent anaphylaxis". Usually this reaction is prompted by exercising within three or four hours of eating a specific type of food.

The symptoms of a severe anaphylactic response exhibit a variety of indicators. These include difficulty breathing, swallowing or speaking, usually caused by swelling in the tissue of the throat and mouth. This, combined with the constriction of the smooth muscle tissue of the lungs, is a reason why a pre-existing asthma condition may complicate anaphylaxis. Swelling and angioedema may occur over the entire body or only in an isolated area. The throat, tongue, lips, eyelids, face, hands and feet are all prone to visible swelling. Raised reddish bumps, or "hives", that cause itching can become visible over a widespread area of the body. Abdominal cramps may be experienced. A person's pulse may also quicken or become irregular due to tachycardia. This is why beta-blockers taken because of pre-existing heart conditions or high blood pressure can worsen any anaphylactic shock by weakening the body's ability to deal with it. A sense of uneasiness or anxiety is another possible indicator. Anaphylactic shock lowers the blood pressure and dizziness, weakness, or unconsciousness may result. In the most extreme cases, circulatory collapse, coma and death can occur.

If the anaphylaxis is only mild then the symptoms will be much more subdued. A localised rash or tingling in the mouth may be the only real indicators. While some people may recover by treatment with antihistamines, the risk is that the condition may develop into a more severe episode over time. This is why caution must be taken if the sufferer has difficulty breathing or swallowing, or they experience a feeling of weakness. The problem with antihistamines in these emergency situations is that they take too long to be absorbed into the bloodstream to be effective during a life-threatening reaction. Also, histamine is not the only substance released during anaphylaxis because there are other mediators involved, such as leukotrienes.

Adrenaline, or epinephrine, is an effective treatment that works to reduce the swelling in the throat, reversing the narrowing of the airways and helping to relax the bronchial tubes. It also reduces the swelling around the face and lips. Adrenaline restores the blood pressure, stimulates the heartbeat and causes the blood vessels to contract, preventing the further leakage of fluids. Adrenaline is a quick-acting hormone that is normally produced by glands above each kidney, enabling the body and mind to produce a 'fight or flight' response in an emergency.

If you know that you are at risk from an anaphylactic response, you should carry adrenaline in the form of a self-administered injection in case of an emergency. The EpiPen auto-injector is specifically designed for this purpose. The injection of adrenaline is only an emergency measure that will stabilise the patient's condition until they can get further treatment, usually at a hospital. In extreme cases, cardiopulmonary resuscitation (CPR) may have to be performed to revive a victim of severe anaphylaxis.

If you have previously experienced anaphylaxis then you will know what symptoms to look for because the same allergen will typically recreate the same symptoms during anaphylaxis. However, just because previous attacks have only been mild does not mean that future episodes of anaphylaxis will not be more severe. Anyone who has previously had an anaphylactic reaction is at risk of a severe allergic reaction. It is important to recognise the symptoms of anaphylaxis and act quickly when a reaction occurs. Even if the anaphylaxis appears to be mild, the patient should be closely observed in case there is any deterioration in their condition. Selected blood or skin tests can be administered by an allergist or doctor, who will also require a detailed discussion of the patient's medical history, in order to help identify what triggered the anaphylaxis.

Prevention is the best way to deal with anaphylaxis. For example, if you know that you are allergic to insect stings then you can wear clothing that completely covers your limbs and extremities and always wear shoes when outdoors. Avoid wearing anything that may attract insects, such as bright colours, perfume, scented cosmetics, or hair spray. If you are allergic to a specific type of medication, always make health workers aware of this and check to make sure that any prescribed medication does not contain what you are allergic to. It has been postulated that frequent or excessive exposure to a particular drug can increase the chances of developing an allergic reaction to it. There is also evidence that this is more likely to result from medicine administered by injection rather than taken orally. If you are hospitalised and have a latex allergy, you should inform your hospital staff of your condition. If it is a particular type of food that you are allergic to, always carefully read the labels of products that you intend to eat. If you are dining out, ask what the ingredients of the meal you are thinking of ordering if you are unsure if it is safe. Be aware that some foods such as bananas, avocado, figs, and kiwifruit may cross react with latex allergy.

The only way to manage a potentially life-threatening allergy like anaphylaxis is to reduce the risks and be prepared in case of an emergency. Get to know all the possible triggers for your condition and learn how to recognise the early warning signs of anaphylaxis. Try to avoid exposure to the relevant allergens. Stay prepared by having an emergency adrenaline auto-injection with you during times when you may potentially be at risk.