Diseases & Conditions
Bee stings can also cause massive allergic reactions
The sudden death of champion hurdler Ross Baillie has highlighted the dangers faced by those suffering from extreme allergies. BBC News Online examines "Anaphylactic Shock", the name for any life-threatening reaction to a seemingly innocent substance.
Anaphylactic shock is an extreme form of allergic reaction to a particular substance, and is often life threatening.
In effect, the body's immune system, which is there to tackle substances or organisms which are a threat, such as bacteria or viruses, decides that something harmless poses a great danger, and launches a massive overreaction
In extreme cases, large quantities of an antibody called immunoglobin E are produced, which cause a variety of effects on the body's cells and tissues.
In particular, it causes the body to release an excess amount of histamine, a dangerous chemical.
The resultant, and usually very swift, effects are muscle contractions and swelling, often closing the throat, making it difficult to breathe.
Sufferers may also experience abdominal pain, vomiting and diarrhoea. Immunoglobin E expands blood vessels, causing a drop in blood pressure, which leads to fainting or unconsciousness.
The most visible signs are often swelling and rashes on the skin, or on the lips and tongue if it is a food allergy.
Bites, stings, and jabs
A variety of substances can trigger this massive immune response.
Among them are insect bites or stings, food - commonly nuts, drugs like morphine or the dye injected prior to X-raying. The horse serum used in the makeup of some vaccines can also cause anaphylactic shock.
Many people suffer severe allergic reactions to certain items, such as pet fur or pollen, but these symptoms are rarely life-threatening, and can normally be treated with anti-histamines - a treatment which reduces the amount of dangerous histamine in the body.
However, these treatments take up to an hour to reach the bloodstream, and true anaphylactic shock requires immediate treatment with adrenaline injection.
Hormone makes body 'fight'
Adrenaline is the "fight or flight" hormone, which is released naturally when the body is in a stressful or dangerous situation.
It makes the heart beat faster, widens the air passages in the lungs, and reverses the widening of the blood vessels caused by immunoglobin E.
Most people who realise they have severe allergy reactions carry a ready-filled adrenaline injector with them at all times.
However, such is the speed with which anaphylactic shock takes hold, even immediate treatment with adrenaline is not guaranteed to save the victim's life.