Do you know someone who is ill? There are many types of illness. Some are vague and soon pass, such as having a headache or feeling sick or faint. These brief feelings are not usually called diseases. Injuries such as cuts, sprains or bruises are not counted as diseases either.



When the body does not work properly for a specific reason, which produces effects known as signs and symptoms, it may have a disease. There are thousands of different diseases, affecting different parts of the body. These different diseases have different causes and effects. Nearly all diseases have proper medical names. The study of diseases, how to identify and treat them, and how to prevent them, are all parts of medicine.

Animals, plants and other living things can all suffer from diseases. Some diseases affect animals as well as people. These include the skin condition called ringworm, which is caused by a fungus, and anthrax, an infection caused by a germ called Bacillus anthracis. However, most diseases are limited to just a few particular kinds of living things.


An acute disease tends to come on suddenly and usually lasts a short time. A chronic disease lasts for longer, from weeks to years. An intermittent or episodic disease comes and goes, causing trouble but then fading away for a time. A self-limiting disease is one that stops getting worse and usually gets better, by itself. A progressive disease tends to become steadily more serious. So a common cold is acute and self-limiting, while asthma is episodic and cystic fibrosis (which affects the airways and lungs) tends to be chronic and progressive.


Each disease causes a recognizable group of symptoms and signs. A symptom is something that the patient notices and can describe to a doctor. Symptoms might include tenderness or pain in body parts, swellings, soreness, skin rashes, and spots, wheezing, coughs, sneezes, trembling, loss of feeling or numbness, loss of movement or paralysis and fever (raised body temperature).

Signs tend to be the effects of the disease that the doctor finds when checking or examining the patient. They include blood pressure that is higher than normal or an unusual “murmur” sound from the heart. The doctor may send samples of body parts or fluids, such as blood, to a medical laboratory for testing. Or the patient may attend a medical centre or hospital for tests such as X-rays and scans that see inside the body.


From the symptoms, signs and test results the doctor can usually identify and name a disease. This is called diagnosis. Then the doctor advises, or prescribes, the best treatment or therapy for the disease.

Sometimes in daily life, a symptom such as a headache is regarded as a disease. However, a headache is not a disease in itself. It is a symptom that is caused by an underlying disease or other problem. If a headache is not serious and soon goes, there may be no need to search for its cause. But if it is more severe and long-lasting, the doctor may begin to search for an underlying disease.


One way of grouping diseases is by the parts of the body they affect. Cardiovascular diseases cause problems with the heart and blood vessels. Pulmonary diseases such as pneumonia and bronchitis affect the lungs and airways. Neurological diseases cause problems with the brain and nerves. Gastrointestinal diseases affect the stomach and intestines (guts).


Another way of grouping diseases is of their cause. One of the biggest groups is infections. An infectious disease is the result of the invasion of the body by germs—tiny living things or micro-organisms such as bacteria and viruses. Infectious diseases can be passed from one person to another, either directly by touch, or indirectly in different ways, such as from germs floating in the air. During the stage when a person can pass germs to others, the disease is said to be contagious. There are hundreds of infectious diseases, ranging from common colds and sore throats to very serious conditions such as rabies and AIDS (acquired immune deficiency syndrome).


Some diseases are caused by substances taken into the body. People may be exposed to these substances during work, for example, dangerous chemicals in a factory. The substances could be in the surroundings or environment, for example, harmful chemicals in the air that have been polluted by traffic fumes. Or they could be taken in by choice due to an unhealthy lifestyle. Harmful substances taken in by choice include tobacco smoke, illegal drugs, and too much alcohol.


Some diseases are known as malignancies or cancers. The human body is made up of trillions of microscopic building blocks called cells. These are continually replacing themselves, as part of normal body maintenance. In a cancerous disease, some of these cells begin to multiply out of control. They form lumps or growths known as tumours. Different types of cancer affect various body parts. For example, leukaemias are types of cancer affecting the blood. Sometimes the cause is unknown. In other cases, the cause is clear, such as the carcinogens (cancer-causing substances) in tobacco smoke, which produce lung cancer.



Some diseases can be the result of faulty genes. Genes are like a list of instructions for how a living thing grows, develops and carries out its life processes. Human genes are in the form of a chemical substance called DNA (deoxyribonucleic acid), also known as the genetic material, in each cell of the body. Sometimes genes become faulty and cause diseases that are passed from parent to offspring. An example is haemophilia, in which the blood does not clot properly to seal a cut.


The body has a self-defence or immune system to protect it against most germs and diseases. However, this system can sometimes go wrong. The body then attacks itself by mistake, causing an autoimmune disease. An example is rheumatoid arthritis of the joints.


Doctors and medical scientists continue to find out more about diseases. They study the new ones that appear now and then, such as SARS (severe acute respiratory syndrome) in 2002, and they try to develop better treatments and cures. We can also do plenty for ourselves. A healthy lifestyle, and reporting symptoms to a doctor as soon as possible, helps to reduce the illness and suffering caused by diseases.

Did you know?
• Chickenpox is not named after chickens. People used to think that the pimples caused by chickenpox looked like chick-peas that had been put onto the skin.
• More people in the UK die of cancer than of any other disease.
• You have probably suffered from acute nasopharyngitis several times. This is a name for the common cold, which can be caused by over a hundred different kinds of virus.