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The first report of an allergic reaction was written by the ancient Egyptians: King Menses died about 5500 years ago after being stung by a bee.

So, what exactly is an allergy?

Richard III

An allergy is the state of being hypersensitive to a substance (an allergen) that is harmless to most people. The Romans knew about allergies; in fact, one allergy may have changed the course of Roman history. The emperor Claudius had a son called Brittannicus. He suffered from an allergic reaction to horses causing his eyes to swell up to the point where he was effectively blind. This allowed Claudius’s adopted son, Nero, to be chosen to succeed as emperor. Nero turned out to be not a very nice guy having Britannicus and is his own mother murdered and generally proving to be a bit of a disaster for Rome.

Also, King Richard III, the 15th century King of England and by all accounts not a very nice man, was known to be allergic to strawberries. This is probably why he never visited Wimbledon!

Many, many more famous people have allergies. These include Beethoven, Dickens, Alice Cooper, Drew Barrymore and Bill Clinton.

Famous people with allergies

What is an allergic reaction?

An allergic reaction happens when the body’s immune system is triggered by a substance that it thinks is foreign or dangerous but is in fact harmless.

The immune system is brilliant at defending the body from invaders like unfriendly bacteria and viruses (germs...otherwise know as pathogens). Every day you breathe in thousands of them; they are in the air around us all the time. Your immune system identifies and destroys them all. Very occasionally a virus or bacteria will be missed and you catch a cold, get a sore throat or worse. You will soon recover from your cold because the immune system never gives up. Once it realises it has missed an invader it responds to destroy it. That is why you will always recover from a cold. Your immune system will get it in the end!

Immune System Response

If you are bitten by an insect you will develop a red itchy lump. This is a sign that your immune system is doing its job killing any germs that may have got into your body.

The immune system is really valuable piece of kit. Without it people die. This is what happens when a person gets AIDS (Acquired Immunodeficiency Syndrome). The HIV virus attacks the immune system and disables it. It’s not the HIV virus that kills the patient it is all the other germs in the victim’s environment that do the damage because the immune system can no longer fight them.

How does the immune system work?

This a very good question. The body has many ways of fighting infection and new mechanisms are still being discovered but the main response goes like this:

Macrophages are white blood cells whose job is to eat and digest foreign bodies and the remainder of old cells. The name comes from ancient Greek and means big eaters (macro = big, phagein = eat). Some of these foreign objects will be germs (viruses and bacteria:a virus causes things like HIV while bacteria causes things like a sore throat). These will be consumed and destroyed. Bits of the pathogen are however kept and displayed on the surface of the macrophage cell. A pathogen is anything that causes a disease.

T-helper cells are also present in the blood, these interact with the macrophage and pick up the message that there are pathogens of this particular type around in the body. The T-helper cell then releases a chemical messenger (interleukin) which causes the body to produce two new kinds of cells: cytotoxic B-cells and T-cells.


T- cells are the hunter killers of the immune system. The T - cells produced will now recognise any cell infected with a pathogen. They will bind to it and release a toxic chemical that kills the infected cell and the pathogen.

The B-cells can also recognise this particular antigen (an antigen kick starts the immune response). They go on to differentiate into plasma cells. These produce millions of antibodies specific to the antigen. An antibody is basically a label that will automatically stick to any pathogen that it finds. It basically says, ‘come and get me boys, I’m dangerous’.

Macrophages then hunt down the labelled pathogens and destroy them. What’s more, some of the B cells change into ‘memory B-cells’. These can hang around in the system for decades carrying millions of antibodies specific to that pathogen.

If the body is ever re-infected with the same pathogen the immune response is very quick and savage. This is why it is so rare to get the same disease twice! Every cold you catch is a new one, as you get older you build up a stock of memory B cells of lots of different types, so tend to get fewer colds!

There is another immune response that is also important. This is the one that can go wrong and cause allergic responses. This one involves mast cells. Mast cells are present mostly in tissue not in the blood stream. Mast cells contain cytoplasmic granules which store chemicals which produce inflammation. The release of these chemicals is known as degranulation and may be caused by injury to the tissues by, impact, cutting, burning, or exposure to chemical toxins like venom. Inflammation is, again, a way the body protects itself.

These chemicals call lots of different types of white blood cell, including B- and T-cells, to the site of the injury to help prevent infection. This increases the blood flow which causes the tissue to swell, increase in temperature and look red. This can all feel rather uncomfortable or painful. It is really a sign that your body is doing its stuff and repairing itself as quickly as possible.

So where does the allergic reaction fit in?

Well, one of the chemicals released when the mast cells degranulate is called histamine. This is a powerful chemical. Amongst other things this is designed to dilate blood vessels. This means the bloody vessels get wider so that more can get to the damaged region carrying the much needed B- and T-cells needed to fight infection. It also causes smooth muscle to contract, or go into spasm. Smooth muscle is responsible for causing contraction in the in the intestine (peristalsis) and is found surrounding all the major airways. Both effects can cause problems if the response is too strong.

Most allergic reactions are annoying but harmless. Hay fever is an allergic reaction to pollen. It affects about one fifth of the population in Britain. When plants are producing pollen in spring and summer people are most affected.

Pollen is breathed into the upper airways where an allergic reaction takes place. The mast cells present in the lining of the nose react to the pollen degranulating and dumping Histamine into these tissues. They become inflamed and produce lots of mucus as a result! Bright red eyes and a runny nose! Lovely! This can be very annoying but is not life threatening. They are fairly easily treated with antihistamine drugs which prevent the mast cells from degranulating. Thankfully most allergic reactions are of this type. Some however are not.


This is the most extreme allergic reaction known. The tinniest amounts of allergen can cause a life threatening response from the immune system. Anaphylactic shock, the most severe type of anaphylaxis, occurs when an allergic response triggers a quick release from the mast cells of large quantities of histamines. This causes the veins and arteries to widen (dilate) causing a sudden drop in blood pressure. The smooth muscle surrounding the breathing passages contracts narrowing the airways. Inflammation leads to the mucus membranes going into overdrive producing too much liquid that can block the already dilated passages. Anaphylactic shock can lead to death in a matter of minutes if left untreated.

How do you treat anaphylaxis?

The main treatment is an immediate injection of a dose of adrenalin (epinephrine). Adrenalin is a natural chemical messenger produced by the body, a hormone. Adrenalin acts against all the effects of anaphylaxis. It causes the blood vessels to get narrower (constrict) and combats inflammation. It is really brilliant stuff.

During anaphylaxis, the body tries to produce adrenalin itself but can’t make it in big enough quantities. Sufferers usually carry an EpiPen. This is an autoinjector that contains a big dose of adrenalin. A spring loaded needle shoots out and delivers a large dose of adrenalin straight into the blood stream.

Epi pens and peanuts

What are the main allergens?

Anaphylaxis can be brought on by any allergen but the most common in Britain are insect stings and food allergies. Most notably peanuts! About 1 in 50 children in Britain have some form of peanut allergy. Have you ever noticed the ‘Can contain traces of peanuts’ warning on food packaging? This doesn’t mean the product deliberately has peanuts in its recipe. It just means that it is made in a factory where peanuts have been used somewhere at sometime. Some people are so sensitive to peanuts that even a few millionths of a gram of the allergen can threaten their lives. This really is very scary for all concerned.

May contain nuts

Is there a cure?

Until recently the answer was no. But a team from Addenbrook’s Hospital in Cambridge think otherwise! The treatment may turn out to be surprisingly simple. The team exposed four children to peanuts over a period of six months gradually building up the dose. By the end the children could eat five peanuts a day without showing signs of a reaction.

This may not sound mind blowing but we need to remember that six months previously a single peanut could have put their lives at risk. Every time a person with a peanut allergy thinks about eating just about anything they worry it might kill them. This treatment could help remove the fear and make their lives much less scary. The treatment may not be a permanent cure but as long as sufferers keep on taking their daily dose they should go on remaining tolerant of peanuts.

The big questions:

What is an allergic reaction?

What is anaphalaxis?

How can we treat allergies?

Are allergies becoming more common?

What is an allergen?

Can allergies be cured?