NHS information about sudden confusion (delirium), with links to other useful resources.
Read about oedema (dropsy), which is the medical term for fluid retention in the body. Oedema often causes swelling in the feet and ankles.
Read about salivary gland stones (calculi), which are small stones in the salivary glands in your mouth. Find out what you can do to try to remove them and when to get medical help.
Sarcoidosis is a rare condition that causes small patches of red and swollen tissue, called granulomas, to develop in the organs of the body.
Read about severe acute respiratory syndrome (SARS), a highly contagious, serious and potentially life-threatening form of pneumonia.
Find out about scarlet fever, including the symptoms, what to do if you or your child has it, how it's treated, how long it lasts and how it's spread.
Read about schistosomiasis, also known as bilharzia, an infection caused by a parasitic worm that lives in fresh water in subtropical and tropical regions.
Read about scleroderma, including the different types, symptoms, causes and treatments.
Find out about selective mutism, a severe anxiety disorder that prevents people from speaking in certain social situations.
Read about septic arthritis, which is inflammation of a joint caused by a bacterial infection. It's also known as infectious or bacterial arthritis.
Read about sexually transmitted infections (STIs), including possible symptoms, common types of STI and when to go to a sexual health clinic.
Find out what shin splints are, how they happen, and what you can do about them.
NHS information about shortness of breath, or breathlessness, including when to get medical help and what the cause might be.
Shoulder impingement is a common cause of shoulder pain. Find out about the symptoms, causes and treatments for it.
Sick building syndrome (SBS) is a set of symptoms you get while you're in a particular building. It usually happens in an office, but you can get it in any building.
Read about silicosis, a long-term lung disease caused by inhaling large amounts of crystalline silica dust, usually over many years.
Read about skin cysts, which are fluid-filled lumps underneath the skin. They're common and harmless, and may disappear without treatment. Holding a warm flannel against the cyst can help it heal.
Read about skin tags (small flesh-coloured growths), including why they occur, when they can be a problem and how they can be removed.
Find out about slapped cheek syndrome (also called fifth disease or parvovirus B19), a viral infection that mainly affects children but can affect people of any age. Read about the symptoms and when to see a GP.
Read about sleepwalking, including why it might happen, what you can do about it and when to seek medical advice.
Read about smelly urine, which on its own is not usually a cause for concern. Find out what can cause smelly pee and how to keep it clear and smelling mild
Read more about what to do if you or someone you know is bitten by a snake.
Find out about social anxiety (social phobia), including the symptoms, getting treatment and what you can do yourself to help overcome it.
Find out what soft tissue sarcomas are, what symptoms they can cause and how they're treated.
Find out how to look after your lips when they're exposed to the sun, wind and cold. Applying a lip balm that contains petroleum or beeswax will help treat and prevent dry lips.
Find out how to treat a sore or white tongue. Also, read about the possible causes of a painful tongue, which can include geographic tongue, oral thrush and aphthous mouth ulcers.
Find out what can cause a sore throat, how you can soothe it and when to get medical advice.
Read about what a spirometry test involves and why it's carried out.
Find out NHS information on spleen problems, splenectomy and living without a spleen.
Read about spondylolisthesis, where a bone in the spine (vertebra) slips out of position, either forwards or backwards.
Read about some of the main types of Staphylococcal infections, including how they're spread and how they're treated.
Find out about steroid inhalers, including why they're used, who can use them, and what side effects they can cause.
Steroid injections, also called corticosteroid injections, are anti-inflammatory medicines used to treat a range of conditions. They can be used to treat problems such as joint pain, arthritis, sciatica and inflammatory bowel disease
Find out about steroid nasal sprays, including why they're used, how to use them and possible side effects.
Find out what steroids (corticosteroids) are, when they're used, how they work, and what different types are available.
Steroid tablets, also called corticosteroid tablets, are a type of anti-inflammatory medicine used to treat a range of conditions.
Read about Stevens-Johnson syndrome, which is a rare but serious disorder that affects the skin and mucous membranes.
Read about a stomach ache and abdominal pains, including stomach cramps or an ache in the tummy (abdomen).
Read about the causes of stopped periods and when to seek medical help.
Find out about the medications that can help if you want to stop smoking, including nicotine replacement therapy (NRT), bupropion (Zyban) and varenicline (Champix).
Find out about stretch marks, including where, when and how they occur, what causes them, and how they can be treated and prevented.
Find out about styes, including what causes them, what you can do to treat them and when to see a GP.
Sudden infant death syndrome (SIDS) – sometimes known as 'cot death' – is the sudden, unexpected and unexplained death of an apparently healthy baby.
Sunburn is red, hot and sore skin caused by too much sun. It may flake and peel after a few days. You can treat it yourself. It usually gets better within 7 days.
Find out about the history of swine flu (H1N1) and what the current situation is.
Read more about swollen lymph glands, which are usually a sign of infection.
Read more about melanoma which is a type of skin cancer that can spread to other organs in the body. The most common sign of melanoma is a new mole or a change to an existing mole.
Find out about non-melanoma skin cancer, including the different types of non-melanoma, what causes it, and how it's treated.
Find out about scabies, including symptoms, causes and treatments.
Read about scars, including the different types, how and where they form and how they're treated.
Read about schizophrenia, a long-term mental health condition where you may see, hear or believe things that are not real.
Read about sciatica, which is pain caused by irritation or compression of the sciatic nerve. Find out about the symptoms, what you can do to ease the pain, and when to get medical help.
Find out what scoliosis is, why it happens and how it's treated.
Read about scurvy, a vitamin C deficiency caused by not eating foods (fruit and vegetables) rich in vitamin C for at least a few months.
Read about seasonal affective disorder (SAD), a type of depression that recurs on a seasonal basis. Find out about the symptoms, causes and treatments.
Self-harm is when somebody intentionally damages or injures their body. Support is available for anyone who self-harms or thinks about self-harm, as well as their friends and family.
Find out more about the symptoms of sepsis in children and adults, and where and when to get help.
Read about the signs of a severe head injury, such as seizures, unconsciousness, drowsiness, repeated vomiting, and blood or clear liquid coming from the ears or nose.
Read about shingles, including symptoms and what to do if you think you have it.
Short-sightedness, or myopia, is a very common eye condition that causes distant objects to appear blurred, while close objects can be seen clearly.
Shoulder pain is a symptom rather than a condition in itself. Shoulder disorders are the most common causes of shoulder pain.
Find out about sickle cell disease, a serious inherited blood disorder where the red blood cells develop abnormally. Find out about the symptoms, causes and treatments.
Read about Sjögren's syndrome, which affects parts of the body that produce fluids, like tears and spit (saliva). Find out what the symptoms are, what causes it, how it's treated and advice about living with it.
Find out about sleep paralysis, a temporary inability to move or speak that happens when you're waking up or falling asleep.
Read about slipped disc, including what it is, what causes it, how it's diagnosed and treated, plus how to prevent it.
Read about a small bowel (intestinal) transplant, an operation to replace a diseased or shortened small bowel with a healthy bowel from a donor.
Snoring occurs when a person makes a snorting or rattling noise when they breathe during sleep.
Read about spina bifida, which is a condition where an unborn baby's spine and spinal cord does not develop properly.
Read about spinal muscular atrophy (SMA), a condition that makes the muscles weaker and causes problems with movement that get worse over time.
Information about sports injuries, including possible causes, what to do if you get injured, plus treatment and prevention advice.
Sprains and strains are common injuries affecting the muscles and ligaments. Most can be treated at home without seeing a GP.
Find out what causes a squint and how it's treated. Also, read about the signs to look for in your child and when to see a doctor.
Find out about selective serotonin reuptake inhibitors (SSRIs), including how they work, what they're used for, how long you need to take them for and the potential side effects.
Stammering, or stuttering, is a relatively common speech problem in childhood, but can also persist into adulthood.
Read about statins – medicines that lower the level of low-density lipoprotein (LDL) cholesterol in the blood. Find out why you may be offered them, how they're taken, and the possible side effects.
Read about stem cell or bone marrow transplants, including why they're used, what's involved, and what the potential risks are.
Read about stillbirth, which is where a baby is born dead after 24 completed weeks of pregnancy. Find out the causes of still birth and how to reduce the risk.
Find out more about the symptoms of stomach cancer and when to see a GP.
Stomach ulcers, also known as gastric ulcers, are open sores that develop on the lining of the stomach. Read about the possible symptoms, causes, treatments and complications.
Read about strokes, a serious and life-threatening medical condition that occurs when the blood supply to part of the brain is cut off.
A subarachnoid haemorrhage is an uncommon type of stroke caused by bleeding on the surface of the brain. It's a very serious condition and can be fatal.
Read about subdural haematoma, a serious condition where blood collects between the skull and the surface of the brain. Find out why it happens, what the symptoms are, and how it's treated.
Read more about supraventricular tachycardia (SVT), which is a condition where your heart suddenly beats much faster than normal. SVT is not usually serious but some people may need treatment.
Syphilis is a bacterial infection that's usually caught by having sex with someone who's infected. Find out what the symptoms are, how it's spread and how it's treated.
Read about soiling, which is when a child regularly poos their pants. If they are already potty-trained, the soiling is usually because they are badly constipated. Treatment from a GP can help.
Find out about sinusitis, including the symptoms, how to treat it yourself, how a pharmacist can help, when to see a GP and the treatments they may recommend.
Also called dermatillomania or excoriation disorder, skin picking disorder is where you can't stop picking at your skin. There are things you can try to help yourself, but some people may need professional treatment.
If you or someone you know needs help with day-to-day living because of illness or disability, this website explains your options and where you can get support.
Read more about the causes of swollen arms and hands, what to do about it and when to get help.
Find out about sleep apnoea, which is when your breathing stops and starts while you sleep.