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There are many reasons why we, as humans, could experience a reaction to something in our environment – for example a food, pollen, drug, insect or mould.

One obvious reason is that the substance could be poisonous. If something is poisonous, we experience what is called a “toxic reaction”. With toxic reactions, everyone who is exposed to the substance will have a reaction.

Poisons don’t discriminate – they may be more or less severe in certain individuals, but everybody will respond in some way.

On the other hand, some people will have a reaction to a substance at an amount other people can usually tolerate. This is called a “hypersensitivity”. When you have a reaction to substances in the environment that are harmless to most other people, you’re said to have a “hypersensitivity reaction”.

This type of reaction could happen for different reasons in different people – and this is where the two terms, “allergy” and “intolerance”, come into play.

Allergy and intolerance are both hypersensitivity reactions, but they differ greatly. In an allergy, the immune system causes the reaction; in an intolerance, the reaction is caused by something else – for example, an enzyme that’s missing in your body or not active enough. This might seem like a small distinction, but because of this, the reactions are very different.

Colds and flu

Colds are viral infections of the nose and throat. Colds can go on to involve the sinuses, ears, larynx (vocal cords), trachea and bronchi directly or through secondary effects.

The presence of the virus causes inflammation of membrane linings in the nose, so that there is swelling with obstruction (stuffiness) and increased mucous secretions.

One to three days after exposure, a cold begins with a sore throat, discomfort in the nose, and sneezing. This is soon followed by a running nose and feeling unwell.

Colds are the most common type of respiratory infection. They’re usually mild illnesses that naturally come to an end, only occasionally leading to further problems.

Flu, or influenza, is a viral illness that occurs predominantly in the winter months in South Africa. It’s easily confused with the common cold, which is also a winter viral illness, although caused by other viruses.

Flu spreads easily from person to person through droplet distribution when an infected person coughs or sneezes or, quite commonly, through hand-to-hand contact.

Symptoms can occur abruptly, and it’s sometimes possible to pinpoint the exact hour of the day that symptoms began.

Influenza viruses can infect the nose, throat, sinuses, upper airways and lungs. In healthy children, young adults and middle-aged people, the disease is mostly mild


Everyone coughs from time to time. It’s a vital defence mechanism that clears unwanted material from your lungs, and so it isn’t necessarily a sign of active or approaching illness. It can be merely a once-off effort of the body to clear the air passages.

Coughs can last a few days, such as with a common cold, or be a more chronic cough that could last for months in some instances. A cough, interestingly, was the most common reason why patients went to see a primary care doctor in a recent study conducted in South Africa.

The causes of coughing are varied and many. It can also be a symptom of many different conditions, not always directly related to a lung disease. There are cough receptors located in the respiratory tract, in the oesophagus, the diaphragm and the stomach.

A cough is described as an "explosive expiratory manoeuvre that’ reflexively or deliberately intended to clear the airways". It’s aimed at clearing the throat and the air passage of inhaled irritants, such as dust or dirt particles, and excess secretions, such as mucus. A cough can also be caused by capsaicin-like compounds, such as those found in chillies. Certain chemicals, such as swimming-pool chlorine, are highly irritating to the airways and can also make some people cough.

Digestive health

The main aim of the digestive system is to process the food we eat and drink in order to provide the body with its energy and nutrient needs, and then to deal with its waste products. The energy is needed to ensure our survival and to repair our body tissues.

The digestive tract starts at the mouth and ends at the anus.

Read more here about how the whole digestive system works from start to finish.

A lack of food can lead to starvation and a lack of nutrition can lead to malnutrition. An inability or reduced ability to absorb nutrients from the diet can lead to both starvation and/or malnutrition.

Digestive disorders are the cause of ill health for millions of people the world over and the causes and symptoms of these are numerous. They range from minor, such as slight heartburn or nausea after eating a big meal, to serious, such as colon cancer.

Symptoms of digestive diseases can include diarrhoea, nausea, heartburn, vomiting, constipation, abdominal swelling, abdominal pain, flatulence, bleeding from the digestive tract, and loss of appetite.


Your blood pressure (BP) is the pressure within your blood vessels. This pressure is generated by the contraction of the heart and counteracted by the resistance of the small arteries. BP is essential to life. It keeps the blood flowing through your body and provides oxygen and energy to your organs. 

Your BP is strictly regulated, as too low pressure causes dizziness, fainting, and a lack of oxygen to your organs. In fact, when a doctor uses the term “shock”, it usually implies that there’s been a drastic drop in blood pressure, leading to inadequate blood flow through the body (perfusion) and insufficient oxygenation of vital organs like the brain and kidneys.

Starved from their life-giving source of oxygen, these organs cannot function anymore, and you’re at risk of dying – unless corrective treatment is taken.


Every single person experiences trouble sleeping at some time or another. This could be temporary, such as when the neighbours are having a party, or because you’re nervous about a job interview.

A temporary sleep disruption usually has a discernible cause, and the sleep disruption comes to an end once that particular source of stress or noise is no longer present.

If you constantly feel sleepy during the day, you have difficulty falling or staying asleep at night, you wake up very early, or feel tired when you wake up, you could be suffering from a more serious sleep disorder. You may have had this problem for a long time, so it could start feeling normal to you.

Sleep disorders refer to disturbances that occur within sleep, or in your sleep cycle, that results in daytime consequences and disturbances in occupational and/or social functioning. In other words, these are abnormalities of sleep physiology that have negative consequences.

Furthermore, these negative consequences have to be sustained for a period of time. For example, if you have insomnia symptoms for 2 or 3 days, it doesn’t constitute a disorder. For insomnia to be considered a disorder, you need to experience insomnia symptoms on most nights for a month.

It’s estimated that one in four people suffer from some form of sleep disorder that affects both their productivity and quality of life.


Although stress is something we all talk about, it can be a difficult concept to understand and define. The best place to start may be to view it from a biological perspective.

Humans, like all organisms, have to interact with their environment to fulfill their needs. Stress is what happens when we’re faced with challenges in our environment. It’s important for us to experience challenges as this is how we learn and adapt to our environment, and thus stress can be healthy and natural.

An example of the beneficial aspects of stress can be seen in the effects of exercise on muscle growth. When muscle cells are stressed, such as when we exercise, they become enlarged and the muscles become stronger and better able to perform their tasks in future.

When we’re faced with a stressful situation, pathways in our body are activated to produce a stress response.


A stroke, also known as a cerebrovascular accident (CVA), occurs when an artery that supplies oxygen-rich blood to the brain bursts or becomes blocked by a blood clot. Blood clots cause destruction and swelling and often cause immediate severe neurological deficits.

If a stroke patient survives, neurological damage may substantially improve with time as the blood clot is absorbed. More commonly, if a blood vessel is blocked, cells are deprived of oxygen and die. This is known as an infarction. As a result, the part of the body controlled by those cells can no longer function properly.

Like a heart attack, a stroke requires immediate medical treatment when symptoms are noticed. In some cases, specific treatment can reduce the number of brain cells that are permanently damaged by the stroke.

The effects of a stroke depend on a number of factors, such as the extent of the brain damage and the area of the brain that is affected.

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