What is allergy?

   At some time every year, certain people suffer from sneezing, running nose and watery eyes. They suffer from an allergy. It is usually called hay fever. Their bodies react badly to the pollen from plants and grasses that is blown around in the air in early summer. Some people suffer in the autumn, when there is tree pollen about.
   Pollen is not the only thing that can upset allergic people. There are a great many commonplace things like dust and fur that can start allergies. And coughs and sneezes are not the only reactions found in allergies. Rashes and itches are common also.
   The substances that produce allergies are called 'antigens' or 'allergens'. There are many different sorts. They include proteins from bacteria and pollens, and chemical substances from primulas and many other green plants.
   People may also be allergic to foods. Seasonal fruits and vegetables (particularly straw-berries), shellfish, chocolate, eggs and milk are often the cause of food allergies.
   The body reacts to antigens by producing 'antibodies'. A different antibody is produced for each different antigen. When an antibody reacts with an antigen in the blood stream, the antigen is made harmless. However, if the antigen reaches tissue cells before it meets an antibody, it causes irritation in the cells.
   The irritated tissue produces a chemical called 'histamine'. This seems to be responsible for many of the ill-effects of allergies.
   There are many ways of treating allergies. An obvious one is for the sufferer to avoid contact with the substance to which he is allergic. This is often possible if the substance can be identified. It may be that the sufferer will have to avoid contact with the family cat or change his type of pillow if it is feathers that are the root of the trouble.
   One means of identifying what substances a person is allergic to - his allergens - is called the scratch test. Small scratches are made in a row on the person's body. Tiny amounts of various suspected material like pollen and dust are placed in the scratches. If the skin around a particular scratch soon becomes red and swollen then the doctor knows which substance is the culprit.
   Sometimes it is not possible for a sufferer to avoid an allergen. For instance it is not easy to get away from pollen in the air, even in cities. In this case it may be possible to treat the patient by giving him small doses of the allergen, gradually increasing the dosage. The hope is that he will become used to the allergen and not react so badly.
   Another way is to prescribe drugs known as anti-histamines. These combat the histamine which is always released as part of the allergic reaction.
   Antibodies also protect our bodies from attack by bacteria and viruses. They can prevent illnesses such as measles and mumps. Doctors can inject antibodies to immunize people against diseases. They take great care to make sure that these injections do not cause allergy.