What is sickness?

Sickness is a very unpleasant feeling. You usually feel it in the back of your throat and in your stomach. And you might not actually be sick.

When you feel sick you might also:

• feel dizzy or lightheaded

• make more saliva (spit) than usual

• have a faster heart rate

• have cold, clammy skin

• not want to eat or drink

Being sick means that your stomach muscles tighten up, forcing any food or liquid in your stomach up your throat and out of your mouth. You could feel sick before this happens, but it's not always the case. This is also called nausea.

Retching means trying to be sick, but bringing nothing up. Your chest and stomach muscles contract as if you were going to be sick, but you aren't. You do not always feel sick before retching. It's sometimes also called heaving or dry heaves.

What are the causes of sickness?

There are lots of different causes of sickness. But as far as your body is concerned, it is trying to get rid of something that shouldn't be there.

A part of the brain called the vomiting centre controls being sick. The vomiting centre is in the brain stem.

You might be sick if the vomiting centre receives signals from:

• another part of the brain called the chemoreceptor trigger zone (CTZ)
• your stomach
• your inner ear - caused by motion or vertigo (which is a sensation of loss of balance)
• your senses - especially taste and smell
• your emotions - being frightened or anxious can make you sick

Chemotherapy drugs make your body release chemicals that signal between nerves. These are called neurotransmitters and include serotonin. These chemicals stimulate the chemoreceptor trigger zone (CTZ) and the vomiting centre. 

Anti sickness medicines can block these chemicals and stop the signals getting through. So, they can stop you being sick.

We don't know quite so much about the control of feeling sick. It's probably controlled by the part of the nervous system that regulates things we don't have to think about, like breathing.

Problems with feeling and being sick

Feeling and being sick a lot can cause:

• loss of appetite
• weight loss
• fluid changes in your body which can lead to dehydration
• feeling very tired (fatigue)
• disruption to your daily life

Help for you

Studies show that between 40 and 70 out of 100 people with cancer (between 40 and 70%) will feel sick or be sick at some point. Nausea and vomiting are the treatment side effects that many people with cancer fear most. They can make everyday life very difficult to cope with.