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Lupus

 

Lupus is an uncommon, complex and poorly understood condition that affects many parts of the body and causes many different symptoms ranging from mild to life-threatening. Some common symptoms of lupus include:

  • fatigue
  • skin rash
  • joint pain and swelling

Autoimmune condition

Lupus is an autoimmune condition, which means that it is caused by problems with the immune system (the body's natural defence against illness and infection).

In people with lupus, for reasons that are not clearly understood, the immune system starts to attack healthy cells, tissue and organs. As with other more common autoimmune conditions, such as rheumatoid arthritis, it is thought that a combination of genetic and environmental factors are responsible for triggering the onset of lupus in certain people.

Types of lupus

There are several types of lupus. The main types are:

  • discoid lupus erythematosus
  • drug-induced lupus
  • systemic lupus erythematosus

These are briefly outlined below.

Discoid lupus erythematosus

Discoid lupus erythematosus (DLE) is a mild form of lupus that only affects the skin. It causes symptoms such as:

  • red, circular, scaly marks on the skin that can thicken and scar
  • hair loss
  • permanent bald patches

DLE can usually be successfully controlled using medication and by avoiding exposure to direct sunlight. DLE usually only affects the skin but, in some cases, it can progress to the body's tissues and and organs (systemic lupus erythematosus - see below).

Drug-induced lupus

There are over 100 medications that are known to cause lupus-like side effects in certain people. Lupus caused by medication is known as drug-induced lupus.

Stopping the course of medication will usually help to resolve the symptoms of drug-induced lupus.

If you are concerned that your medication may be causing lupus-like side effects, discuss the issue with your GP. However, do not suddenly stop taking any prescribed medication without first checking with your GP.

Systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a type of lupus that can affect most of the body's tissues and organs. SLE is what most people mean when they use the term "lupus".

The rest of this article will focus on SLE.

How common is lupus?

SLE is an uncommon condition, with 90% of cases occurring in women. Most cases of SLE first begin in women who are of childbearing age (between the ages of 15 and 50).

There are marked differences in how widespread SLE is among different ethnic groups. For example, i:

  • one in every 5,000 white women will develop SLE
  • one in every 1,000 women of Chinese origin will develop SLE
  • one in every 625 Afro-Caribbean women will develop SLE

There is currently no cure for SLE, but there are a range of different medications that can help to relieve many of the condition's symptoms.

Outlook

The outlook for SLE varies widely as the symptoms can range from mild to severe. Many people will experience long periods of time with few or no symptoms before suddenly experiencing a sudden flare-up where their symptoms are particularly severe.

However, even mild cases of SLE can have a considerable impact on a person's quality of life because many of the symptoms, particularly chronic fatigue, can be distressing and cause feelings of depression and anxiety.

With good levels of support from friends, family and healthcare professionals, many people with SLE learn to manage their condition effectively.

SLE can sometimes cause a range of serious complications, such as kidney and heart disease, and the treatment may make a person vulnerable to serious infections. This is why 50 years ago SLE was regarded as a terminal condition, as most people would die of a complication in the first 10 years after being diagnosed.

Thanks to advances in treatments, now most people with SLE have a normal, or near normal, life expectancy.

The symptoms of systemic lupus erythematosus (SLE) can vary from person to person. Some people with the condition may only experience a few mild symptoms, whereas others may be more severely affected.

The symptoms of SLE can also appear in "flare-ups". This means that although you may always have mild symptoms, during a flare-up your symptoms may become more severe. 

Primary symptoms

The three primary symptoms of SLE are:

  • fatigue
  • joint pain
  • skin rashes

These are described in more detail below.

Fatigue

Fatigue is one of the most common symptoms of SLE. You may feel very tired even though you get plenty of sleep. Carrying out everyday tasks, such as household chores or office work, can leave you feeling exhausted.

Many people with SLE have reported that fatigue is the most distressing and disruptive aspect of SLE because it has a negative impact on their work and social life.

Joint pain

If you have SLE, you are most likely to experience joint pain in your hands and feet. You may find that the pain changes from one set of joints to another quite quickly. However, unlike some other conditions that affect the joints, SLE is unlikely to cause your joints to become permanently damaged or deformed.

Skin rashes

In people with SLE, skin rashes most commonly develop on the face, wrists and hands. A rash over the cheeks and the bridge of the nose is particularly common and is known as a "butterfly rash". Skin rashes that are caused by SLE may be permanent and can be made worse with exposure to sunlight. This is known as photosensitivity.

Other symptoms

As well as the primary symptoms listed above, SLE can also cause a number of other symptoms. However, if you have SLE it is unlikely that you will have all of the symptoms listed below, and many people with the condition will only experience the primary symptoms.

Other symptoms of SLE may include:

  • high temperature (fever) of 38C (100.4F) or above
  • swollen lymph glands (small, bean-shaped glands that are found throughout your body, including in your neck, armpits and groin)
  • recurring mouth ulcers
  • hair loss (alopecia)
  • high blood pressure (hypertension)
  • depression
  • dry eyes
  • memory loss
  • migraine
  • anaemia - a condition where a lack of red, oxygen-carrying blood cells can cause fatigue and shortness of breath
  • Raynaud's phenomenon - a condition that limits the blood supply to your hands and feet when it is cold 

Glossary

Aches
An ache is a constant dull pain in a part of the body.
Anxiety
Anxiety is an unpleasant feeling when you feel worried, uneasy or distressed about something that may or may not be about to happen.
Brain
The brain controls thought, memory and emotion. It sends messages to the body controlling movement, speech and senses.
Depression
Depression is when you have feelings of extreme sadness, despair or inadequacy that last for a long time.
Fatigue
Fatigue is extreme tiredness and lack of energy.
Inflammation
Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.
Joints
Joints are the connection point between two bones that allow movement.
Kidney
Kidneys are a pair of bean-shaped organs located at the back of the abdomen, which remove waste and extra fluid from the blood and pass them out of the body as urine.
Pain
Pain is an unpleasant physical or emotional feeling that your body produces as a warning sign that it has been damaged.
Ulcers

An ulcer is a sore break in the skin, or on the inside lining of the body.

 

Useful Links

Systemic lupus erythematosus (SLE) is an autoimmune condition, which means it is caused by problems with the immune system.

The immune system is the body's natural defence against illness and infection. When the immune system detects the presence of an infectious agent, such as a virus or bacteria, it sends specialist cells called antibodies to kill the agent.

However, in cases of SLE, antibodies released by the immune system start to attack healthy tissue, cells and organs.

Most experts think that SLE does not have just one cause. They argue that there may be a number of genetic factors that make people more susceptible to developing SLE. However, it also takes one or more environmental factors to trigger the onset of SLE in people with an existing genetic susceptibility.

Possible genetic and environmental factors are discussed in more detail below.

Genetic factors

It is believed that the genes that you inherit from your parents make you more susceptible to SLE for two main reasons:

  • If you have an identical twin with SLE you have an estimated one-in-four chance of developing the condition yourself.
  • Rates of SLE vary widely among different ethnic groups.

Researchers have identified a number of different genetic mutations that seem to make people more susceptible to developing SLE.

A genetic mutation occurs when the normal instructions that are carried in certain genes become "scrambled", resulting in the body's processes not working normally.

Most of the mutated genes are associated with regulating certain functions of the immune system, which may explain why the immune system in people with SLE starts to malfunction.

Also, some of the mutated genes are contained in the X chromosome. Chromosomes are large blocks of genetic information. Men only have one X chromosome (and one Y chromosome) whereas women have a pair of X chromosomes.

Therefore, women are twice as likely to receive one of the mutated genes. Along with hormonal factors, this may partly explain why SLE is much more common in women than men.

Environmental factors

A number of environmental factors may be responsible for triggering the onset of SLE in vulnerable individuals.

There is limited to moderate evidence to suggest that the following factors may be responsible:

  • exposure to sunlight
  • hormonal changes that occur during a woman's lifetime, such as during puberty or pregnancy
  • medications can trigger drug-induced lupus

The Epstein-Barr virus (EBV) has also been suggested as a possible cause of SLE. However, EBV is a common viral infection that does not usually cause any symptoms at all and in some people can cause glandular fever. 

Genetic
Genetic is a term that refers to genes - the characteristics inherited from a family member.

Systemic lupus erythematosus (SLE) can be a difficult condition to diagnose. This is because the symptoms of SLE are sometimes very similar to a number of other conditions, most of which are far more common than SLE.

SLE may also be difficult to diagnose because the symptoms can vary greatly from person to person. They may also change over time. For example, there may be periods where your symptoms are not very noticeable, or times when they flare up and become more severe.

Blood tests

If your GP suspects that you may have SLE after examining your symptoms, they will need to refer you for a series of blood tests to help confirm the diagnosis.

Some of the blood tests that may be carried out are listed below.

Anti-nuclear antibody test

An anti-nuclear antibody test checks to see whether there is a certain type of antibody cell in your blood, known as the anti-nuclear antibody. Approximately 95% of people with SLE have this antibody.

However, it is possible to have the anti-nuclear antibody without having SLE, so the anti-nuclear antibody test is not a definitive way of testing for the condition. Your GP will need to use other tests to confirm the diagnosis.

Anti-DNA antibody test

An anti-DNA test also checks for a certain type of antibody in your blood. If you have the anti-DNA antibody, it is highly likely you will have SLE. However, the antibody can also be present in people who do not have the condition.

The level of anti-DNA antibodies increases when SLE is more active, so during a flare-up of symptoms your reading from this test may be greater than normal.

Complement level test

Complement is a chemical in the blood that forms part of your immune system. Your GP may test the level of this chemical in your blood to check how active your SLE is. The level of complement in your blood decreases when SLE is more active.

Other tests

Once you have been diagnosed with SLE, you will normally need regular check-ups and tests to monitor how the condition is affecting your body.

If you have SLE it is possible that you may go on to develop other conditions, such as anaemia or kidney problems. Monitoring your condition will allow your doctor to check for these secondary conditions and, if necessary, provide treatment for them as soon as possible.

You may need to have a scan, such as an X-ray, ultrasound scan or a computerised tomography (CT) scan to check whether SLE is affecting your internal organs.

Antibody
Antibodies and immunoglobins are proteins in the blood. They are produced by the immune system to fight against bacteria, viruses and disease.
Blood
Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.
Heart
The heart is a muscular organ that pumps blood around the body.
Kidney
Kidneys are a pair of bean-shaped organs located at the back of the abdomen, which remove waste and extra fluid from the blood and pass them out of the body as urine.

There is currently no cure for systemic lupus erythematosus (SLE). However, treatments are available that can help to ease your symptoms and minimise the effect that the condition has on your daily life.

Protecting yourself from the sun

Exposure to sunlight can sometimes make SLE symptoms such as skin rashes worse. Therefore, it is important to make sure you protect your skin when you are out in the sun.

This means wearing clothing that covers your skin, including a wide-brimmed hat and sunglasses. When you are out in the sun, you also need to apply sun screen with a high factor (SPF 50) to help reduce your risk of having a flare-up.

If your SLE symptoms are very mild, you may not need any specific treatment. However, most people will require some sort of medication to help them to manage their symptoms.

Some of the medicines that you may need if you have SLE are described below.

Non-steroidal anti-inflammatory drugs (NSAIDs)

Non-steroidal anti-inflammatory drugs (NSAIDs) are a form of painkilling medication that reduce inflammation in the body.

If you experience joint or muscle pain as a result of SLE, you may be prescribed a NSAID to help ease your symptoms. 

Commonly prescribed NSAIDs for SLE include:

  • ibuprofen
  • naproxen
  • diclofenac
  • piroxicam

You can buy some NSAIDs, such as ibuprofen, over the counter. These NSAIDs may be suitable if your joint or muscle pain is mild. However, if your pain is more severe, you will need stronger medication prescribed by your GP.

NSAIDs may not be suitable for people who have stomach, kidney or liver problems or have had these problems in the past. They may also be unsuitable for people with asthma. Children under the age of 16 should not take aspirin. Your GP will be able to advise you about which NSAID is right for you.

If taken in high doses or over long periods of time, NSAIDs can damage your stomach lining, which may cause internal bleeding. If you need to take NSAIDs on a long-term basis, your GP will carefully monitor your condition to ensure that the medication is not causing bleeding from your stomach. However, if this occurs other options are available.

Hydroxychloroquine

Hydroxychloroquine is a type of medicine that is usually used to treat malaria but it is also effective in treating some of the symptoms of SLE, such as skin rashes, joint and muscle pain and fatigue.

You will usually have to take hydroxychloroquine for 6-12 weeks before you start to notice any benefit.

Many people with SLE take hydroxychloroquine on a long-term basis as a way of controlling their symptoms and helping to prevent flare-ups.

Side effects of hydroxychloroquine are rare but may include:

  • indigestion
  • diarrhoea
  • headaches
  • skin rashes

Hydroxychloroquine has also been known to cause more serious side effects in a small number of people. For example, approximately one in 2,000 people taking this medicine may experience damage to their vision. It is worthwhile having a baseline eye check at you local ophthalmic optician but, as side effects are so rare, routine monitoring in an eye clinic is no longer recommended.

Contact your GP or specialist immediately if you experience vision problems while taking hydroxychloroquine.

If your GP or specialist feels it is necessary, you may need to have regular eye examinations to help reduce your risk of developing complications.

Corticosteroids

Corticosteroids are a type of medicine that helps to reduce inflammation quickly. They are are very effective but are usually only prescribed if you have severe SLE.

If you have severe symptoms of SLE, or if you are experiencing a flare-up, you may be given a large dose of corticosteroids to help bring your symptoms under control. As your symptoms ease, your dosage can gradually be reduced.

When prescribing corticosteroids, the lowest effective dosage is always given. This is because high doses or long-term use of corticosteroids can cause side effects. These may include:

  • thinning of your bones
  • thinning of your skin
  • weight gain
  • muscle wasting
  • high blood pressure (hypertension)
  • high blood sugar (with tendency to diabetes)  

Corticosteroids are a safe and effective form of treatment provided that they are taken correctly and under the careful supervision of your GP or specialist. They will tailor the steroid dose to your disease activity to minimise side effects while effectively controlling the condition.

Corticosteroids are not the same as anabolic steroids, which are sometimes used by athletes and bodybuilders to improve their performance.

Immunosuppressants

Immunosuppressants are a type of medicine that suppress your immune system. They can help improve your symptoms of SLE by limiting the damage that your immune system causes when it attacks the healthy parts of your body.

Commonly prescribed immunosuppressant medicines include:

  • azathioprine
  • mycophenolate mofetil
  • cyclophosphamide

Immunosuppressants are sometimes used in conjunction with corticosteroids (see above) because these medicines may ease your symptoms more effectively when used together. In addition, use of immunosuppressant medication may reduce the dose of corticosteroids that is needed.

Immunosuppressant medication is usually only prescribed if you have severe SLE. This is because this type of medication is very powerful and can cause side effects such as:

  • loss of appetite
  • nausea
  • vomiting
  • stomach pain
  • diarrhoea
  • swollen gums
  • bruising or bleeding more easily
  • convulsions
  • dizziness
  • headache
  • acne
  • extra hair growth
  • weight gain

The exact side effects will depend on which immunosuppressant is prescribed. Tell your GP if a side effect becomes particularly troublesome because your dose may need adjusting.

Mycophenolate and cyclophosphamide can cause birth defects in women, so you should use a reliable form of contraception if you are taking these medications and you are sexually active.

If you are trying to become pregnant, an alternative medication such as azathioprine can be used. Pregnancy should be planned in consultation with your specialist during a time of when SLE is in remission (a period when there is a decrease in symptoms). Close monitoring by your specialist and your obstetrician will be essential during pregnancy.

Suppressing your immune system increases your risk of developing infections. Immunosuppressants can also sometimes cause liver damage. For these reasons, you will need to have regular check-ups and blood tests when you are taking immunosuppressant medication. 

Report any symptoms of an infection to your GP immediately, because you may need prompt treatment to prevent serious complications from occuring.

Symptoms of infection include:

  • high temperature (fever) of 38C (100.4F) or above
  • new onset of cough, phlegm or breathlessness
  • burning on passing urine or blood in the urine (haematuria)
  • diarrhoea
  • headache plus fever

You should avoid contact with anyone who is known to have an infection even if it is an infection that you were previously immune to, such as chickenpox or measles. This is because your previous immunity to these conditions will probably be suppressed (lowered).

Rituximab

Rituximab is a new type of medication that can treat people with SLE who don't respond to the medications listed above.

Rituximab was originally designed to treat certain types of blood cancer, such as lymphoma. However, it has since proved to be effective in treating a number of autoimmune conditions, such as SLE and rheumatoid arthritis.

Rituximab works by locking on to and killing the B-cells, which produce antibodies that are responsible for the symptoms of SLE. It is administered directly into your vein over the course of several hours. This is known as an infusion.

Common side effects of rituximab include:

  • flu-like symptoms, such as chills and a high temperature while the medication is being given
  • dizziness
  • nausea
  • vomiting

In rare cases, rituximab can cause infusion reactions. Most infusion reactions occur during or shortly after the administration of the infusion treatment. You will therefore be closely monitored once your treatment begins.

If you start to experience the symptoms of an infusion reaction, such as rash, shortness of breath or chest pain, anti-allergy medicines such as anti-histamines and corticosteroids can be used to help relieve your symptoms.

You need to talk to your doctor as to whether this drug is suitable for your condition.

People with the condition should be aware that there are uncertainties about how effective or safe rituximab is in treating SLE. However, although rituximab is unlicensed, there may be instances where your specialist may consider it to be an appropriate treatment for you.

Glossary

Anti-inflammatory
Anti-inflammatory medicines reduce swelling and inflammation.
Blood
Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.
Corticosteroids
Corticosteroid is a naturally occurring hormone produced by the adrenal gland, or a synthetic hormone having similar properties. It is used to reduce inflammation, so reducing swelling and pain.
Dose
Dose is a measured quantity of a medicine to be taken at any one time, such as a specified amount of medication.
Gut
The sac-like organ of the digestive system. It helps digest food by churning it and mixing it with acids to break it down into smaller pieces.
Immune system
The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses.  
Inflammation
Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.
Joint
Joints are the connection point between two bones that allow movement.
Pain
Pain is an unpleasant physical or emotional feeling that your body produces as a warning sign that it has been damaged.
Physiotherapy
Physiotherapy is a treatment that uses physical movements, massage and exercise to relieve illness or injury.
Remission
Remission is when the symptoms of a condition are reduced (partial remission) or go away completely (complete remission).

If your symptoms of systemic lupus erythematosus (SLE) are mild or well-controlled, you may find it barely affects your day-to-day life and you may not have complications.

You may also find your SLE symptoms significantly improve with age. Many people who are over 50 often find that their SLE symptoms have eased. In some (but not all) people, SLE may improve after the menopause (when a woman's monthly periods stop, usually at around the age of 50).

However, for some people SLE can be a more serious condition that can sometimes cause life-threatening complications. Some of the possible complications that can be experienced are outlined below.

Cardiovascular disease

Cardiovascular disease (CVD) is a general term for any type of health condition that affects the heart and arteries.

Examples of CVD include:

It is estimated that people with SLE are seven to eight times more likely to develop CVD than the general population. The reason for this is that SLE can cause inflammation of your heart and arteries, making it more likely that you will develop CVD.

By taking steps to lower other known risk factors for CVD, you can help compensate for the increased risk of developing CVD as a result of having SLE. These include:

  • quitting smoking (if you smoke)
  • eating a balanced healthy diet low in saturated fat, sugar and salt and contains plenty of fruit and vegetables (at least five portions a day)
  • maintaining a healthy weight
  • taking regular exercise - at least 30 minutes a day, three to four days a week (the exercise should be strenuous enough to leave you slightly out of breath)
  • if you drink, making sure that you stick to the recommended guidelines for alcohol consumption (see below)

The recommended daily limits of alcohol consumption are:

  • three to four units of alcohol for men
  • two to three units of alcohol for women

A unit of alcohol is equal to about half a pint of normal strength lager, a small glass of wine or a pub measure of spirits.

In some people, SLE can cause a number of other heart conditions that are usually less serious such as:

  • pericarditis - inflammation of the lining of your heart
  • myocarditis - inflammation of the muscles of your heart

Lupus nephritis

Lupus nephritis is a potentially serious kidney disease that is caused by prolonged inflammation of your kidneys as a result of SLE. Lupus nephritis is a common complication of SLE that is estimated to affect around half of people with the condition.

Lupus nephritis tends to develop relatively early on in the course of SLE, usually within five years of receiving a diagnosis.

Symptoms of lupus nephritis include:

  • swelling of your feet
  • headaches
  • dizziness
  • blood in your urine
  • a frequent need to urinate

In many cases, lupus nephritis does not cause any noticeable symptoms. However, this does not mean that the condition is not dangerous as it can cause damage to your kidney. Lupus nephritis can also cause high blood pressure (hypertension), which if not treated can put you at risk of developing a serious CVD in the long-term, such as a heart attack or stroke.

It is likely you will be referred for regular blood tests so the condition of your kidneys can be carefully monitored.

If you develop lupus nephritis, it can usually be successfully controlled using immunosuppressants such as azathioprine, mycophenolate mofetil or cyclophosphamide.

Other autoimmune conditions

Approximately one in three people with SLE also have another autoimmune condition, such as thyroid disease, Sjogren's syndrome or Hughes syndrome (antiphospholipid syndrome).

Sjogren's syndrome

Sjogren's syndrome is a condition that damages your salivary and tear glands, causing you to have a dry mouth and eyes. It affects one in eight people with SLE. See the Health A-Z topic about Sjogren's syndrome for more information.

Hughes syndrome (antiphospholipid syndrome)

Hughes syndrome (antiphospholipid syndrome) can occur as a secondary condition to SLE or it can occur on its own.

Hughes syndrome causes an increased risk of clots developing in the arteries (leading to strokes and heart attacks) and the veins (leading to deep vein thrombosis).

Women with SLE and Hughes syndrome also have an increased risk of developing complications during pregnancy. They have an increased risk of miscarriage and premature delivery.

Diagnosis of Hughes syndrome (antiphospholipid syndrome) in cases of SLE requires the presence of either vascular and/or pregnancy-related complications together with antiphospholipid antibodies in the blood.

See the Health A-Z topic about Hughes syndrome for more information on this condition.

Pregnancy

SLE does not usually affect fertility, although many people with the condition also have Hughes syndrome (see above), which increases the risks of complications occurring during pregnancy, such as:

  • miscarriage
  • stillbirth
  • premature delivery

Treatments such as aspirin and heparin injections are available, which increase the chance of a successful pregnancy in patients with Hughes syndrome.

There is also a risk that women with lupus will experience a flare-up of their symptoms during pregnancy.

Symptoms of SLE that can develop during pregnancy include:

  • hair loss
  • swelling of the feet and hands
  • facial redness
  • anaemia
  • muscle, bone and joint pain

Some symptoms may be difficult to distinguish from those related to pregnancy itself, such as anaemia. The risk of flare-ups can usually be reduced by taking anti-malarial medications and appropriate immunosuppressants, such as azathioprine. If necessary, corticosteroids can also be given.

To reduce the risks of complications developing during pregnancy you may be advised to delay your pregnancy until you have gone for six months without experiencing a flare-up of your symptoms and your kidney functions are normal or nearly normal.

While no medication is guaranteed as being safe to use during pregnancy, the medications that are known to be safest are:

  • hydroxychloroquine - an anti-malarial medication
  • azathioprine - an immunosuppressant
  • prednisolone - a corticosteroid

Glossary

Blood
Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.
Blood vessel
Blood vessels are the tubes in which blood travels to and from parts of the body. The three main types of blood vessels are veins, arteries and capillaries.
Fatigue
Fatigue is extreme tiredness and lack of energy.
Fever
A fever is when you have a high body temperature (over 38C or 100.4F).
Heart attack
A heart attack happens when there is a blockage in one of the arteries in the heart.
Inflammation
Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.
Kidney
Kidneys are a pair of bean-shaped organs located at the back of the abdomen, which remove waste and extra fluid from the blood and pass them out of the body as urine.
Lungs
Lungs are a pair of organs in the chest that control breathing. They remove carbon dioxide from the blood and replace it with oxygen.
Oxygen
Oxygen is an odourless, colourless gas that makes up about 20% of the air we breathe.

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.