Acanthosis nigricans is the term for darkened, thickened patches of skin in the armpit and around the groin and neck. Find out about the main causes and treatments.
Achalasia is a disorder of the gullet (oesophagus) where it loses the ability to move food along. The valve at the end of the gullet also fails to open
Find out about first aid and treatment for acid and chemical burns, including burns from acid attacks.
An acoustic neuroma is a type of non-cancerous (benign) brain tumour. Find out about the symptoms, treatments and outlook for this condition.
Acromegaly is where the body produces too much growth hormone, leading to the excess growth of body tissues over time.
Actinic keratoses are scaly patches of skin caused by damage from years of sun exposure. Find out why they shouldn't be ignored and how they're treated.
Read about acupuncture, a treatment derived from ancient Chinese medicine in which fine needles are inserted at certain sites in the body to relieve or prevent health problems
Read about acute cholecystitis, which is inflammation of the gallbladder. It usually occurs when a gallstone blocks the cystic duct.
Acute kidney injury (AKI) is sudden damage to the kidneys that causes them to not work properly. It can range from minor loss of kidney function to complete kidney failure.
Read about acute respiratory distress syndrome (ARDS), which is a life-threatening condition where the lungs can't provide the body's vital organs with enough oxygen.
Read about an adenoidectomy, a surgical procedure to remove the adenoids. Find out what the adenoids do, when they need to be removed and how the procedure is carried out.
An air or gas embolism is a serious problem that can affect scuba divers. Read about the causes, symptoms and treatments.
Read about alcohol poisoning, which occurs when a person drinks a toxic amount of alcohol, usually over a short period of time. This is often known as binge drinking.
The Alexander technique teaches improved posture and movement, which is believed to help reduce and prevent problems caused by unhelpful habits.
Read about alkaptonuria, or "black urine disease", a rare inherited disorder that can turn urine and parts of the body a dark colour and lead to a range of other problems over time.
Information about amputation, including why and how it's carried out, recovery and rehabilitation, prosthetics, stump care and possible complications.
Amyloidosis is a group of rare but serious conditions caused by deposits of abnormal protein called amyloid found in tissues and organs throughout the body.
Anabolic steroids are prescription-only medicines that are sometimes taken without medical advice to increase muscle mass and improve athletic performance.
Find out about different types of anaesthetics, how they work, and the potential side effects. Also, read about the role of the anaesthetist.
Read about the symptoms of anal cancer, how it's diagnosed and treated, plus what causes the condition.
Find out about common and less common causes of anal pain (pain in the bottom), and when to get medical advice.
Read about Angelman syndrome, a genetic disorder that affects the nervous system and causes severe physical and intellectual disability
Read about what to do if you have been bitten by an animal or person, what treatment you may need, and how to reduce your chances of being bitten.
Anosmia is the medical term for loss of the sense of smell. It's usually caused by a nasal condition or brain injury, but some people are born without a sense of smell (congenital anosmia)
Find out about antacids, a type of medication used to control the acid levels in your stomach.
Antihistamines are a type of medicine often used to treat allergies. Find out about the different types, who can take them and what side effects they can cause.
Find out what antisocial personality disorder is, what the signs are, and how it's diagnosed and treated.
NHS Choices information on anxiety disorders in children and teenagers, with links to other useful resources
Arrhythmias or heart rhythm problems are experienced by more than 2 million people a year in the UK. Most people with an abnormal heart rhythm can lead a normal life if it is properly diagnosed.
Arterial thrombosis is a blood clot in an artery. Find out why it happens and how it can be treated.
Asbestosis is a long-term (chronic) lung condition caused by prolonged exposure to asbestos. Asbestos is a soft, greyish-white material that does not burn.
Find out about aspirin, including what it's used for, who can take it, and what the main side effects are.
Find out about atherosclerosis, a potentially serious condition where arteries become clogged with fatty substances. Read about the problems this can cause and who's at risk.
Read about athlete's foot, a common fungal infection of the foot. Find out about the symptoms, what causes it, and how it's treated.
Find out about auditory processing disorder, a hearing problem where the brain is unable to process sounds in the normal way.
Read about age-related cataracts. In older people, changes can occur in the lens of the eye, making it less transparent and causing cloudy or misty vision.
Find out what an abdominal aortic aneurysm (AAA) is, what symptoms it can cause, who's at risk of getting one, and how it can be treated.
Find out who is offered abdominal aortic aneurysm (AAA) screening, why it's done and what it involves.
Read about skin abscesses and internal abscesses. An abscess is a painful collection of pus, usually caused by a bacterial infection.
Acne is a common skin condition that affects most people at some point. It causes spots, oily skin and sometimes skin that's hot or painful to touch.
Actinomycosis is a rare type of bacterial infection caused by actinomyces bacteria. The four main types are oral cervicofacial, thoracic, abdominal and pelvic.
Information about acute lymphoblastic leukaemia including symptoms, causes, treatment, complications and outlook.
Read about acute myeloid leukaemia (AML), an aggressive cancer of the myeloid cells. Information about signs and symptoms, causes, diagnosis and treatment.
Acute pancreatitis is a serious condition where the pancreas becomes inflamed over a short period of time.
Addison's disease, also known as primary adrenal insufficiency or hypoadrenalism, is a rare disorder of the adrenal glands.
Read about agoraphobia, a fear of being in situations where escape might be difficult or that help wouldn't be available if things go wrong.
Albinism is an inherited condition that affects the production of melanin, the pigment that colours the skin, hair and eyes.
Alcohol misuse is where a person consumes excessive amounts of alcoholic drinks.
Alcohol-related liver disease (ARLD) refers to liver damage caused by excess alcohol intake. There are several stages of severity and a range of associated symptoms.
Find out about allergic rhinitis, a condition where the inside of the nose becomes inflamed by allergens, such as pollen, dust, mould or flakes of animal skin.
Read all about allergies, including about the most common allergies, what the symptoms of an allergic reaction are, and what can be done to keep an allergy under control.
All you need to know about altitude sickness, including symptoms, medication, prevention and treatment.
Alzheimer's disease is the most common cause of dementia. Dementia is a group of symptoms associated with a decline in the way your brain functions, affecting your memory and the way you behave.
Read about amniocentesis, a diagnostic test carried out during pregnancy to assess whether the unborn baby could develop a genetic or chromosomal condition.
Read about anal fissures and the importance of seeing your GP if you have one. Also, read about the symptoms, causes, treatment and prevention of anal fissures.
Read about anal fistulas, small tunnels that develop in the skin near the anus. Find out about the symptoms, causes and treatments.
Find out about the symptoms of anaphylaxis, how to treat it, why it happens and how to prevent it.
Androgen insensitivity syndrome (AIS) is a rare condition that affects the development of a child's genitals and reproductive organs.
Angina is chest pain that occurs when the blood supply to the muscles of the heart is restricted. It usually happens because the arteries supplying the heart become hardened and narrowed.
Find out what angioedema is, what the symptoms are, why it happens and how it's treated.
Angiography is a type of X-ray used to examine the blood vessels. Find out why it's used, what it involves and what the possible risks are.
Read about ankylosing spondylitis (AS), a long-term (chronic) condition in which the spine and other areas of the body become inflamed.
Find out what anorexia nervosa is, what causes it, the signs to look out for, and the treatment and support available.
Antibiotics are used to treat or prevent some types of bacterial infection. Find out about the main types of antibiotics, when they are needed, how to take them and the main side effects.
Anticoagulants are medicines that reduce the ability of the blood to clot. Read about why they're used, how you take them and what you need to bear in mind while taking them.
Antidepressants are a type of medication used to treat clinical depression or prevent it recurring. They can also be used to treat some other conditions.
Antiphospholipid syndrome (APS), also known as Hughes syndrome, is a disorder of the immune system that causes an increased risk of blood clots.
An aortic valve replacement involves removing a faulty or damaged valve and replacing it with a new one made from synthetic materials or animal tissue.
Aphasia is a communication disorder that makes it difficult to read, write or speak.
Find out about appendicitis, a painful swelling of the appendix, including what causes it, when to get medical help and how the appendix is surgically removed (appendicectomy or appendectomy).
Arthritis is a common condition that causes pain and inflammation in a joint. Although there's no cure for arthritis, there are many treatments that can help slow it down.
Find out about arthroscopy, which is a type of keyhole surgery used to diagnose and treat joint problems.
Aspergillosis is the name of a group of fungal conditions caused by a mould called aspergillus.
Find out what asthma is, what the symptoms are, what causes it and how it's treated.
Astigmatism is a common and usually minor condition of the eye that causes blurred or distorted vision.
Ataxia is the term for a group of disorders that affect co-ordination, balance and speech. Find out about the main types, what causes them, and how they're treated.
Read about atopic eczema (atopic dermatitis), a condition that causes the skin to become itchy, red, dry and cracked
Atrial fibrillation is a heart condition that causes an irregular and often abnormally fast heart rate.
Read about attention deficit hyperactivity disorder (ADHD), a group of behavioural symptoms that include inattentiveness, hyperactivity and impulsiveness.
Find out about autosomal dominant polycystic kidney disease (ADPKD), an inherited condition that causes small fluid-filled sacs called cysts to develop in the kidneys.
Autosomal recessive polycystic kidney disease (ARPKD) is a rare inherited childhood condition where the development of the kidneys and liver is abnormal.
Find out about age-related macular degeneration (AMD), which mainly affects people over 50 years of age and usually leads to a gradual loss of central vision.
Find out what an abortion involves, how you can get one on the NHS, and what support is available to help you make a decision.
Find out about antifungal medicines, which are used to treat fungal infections such as thrush and athlete's foot
NHS guide to autism. Find out what autism is and what the common signs are. Get help and advice if you or your child are autistic.