Read about male menopause, where some men develop depression, loss of sex drive, erectile dysfunction and other physical and emotional symptoms when they reach their late 40s to early 50s.
Read about phimosis (tight foreskin), which is normal in babies and toddlers. It's usually only a problem if it causes redness, soreness or swelling.
Temporomandibular disorder (TMD) is a problem affecting the 'chewing' muscles and the joints between the lower jaw and the base of the skull.
A tension-type headache is the most common type of headache and the one we think of as a normal, everyday headache.
Information about tetanus, a rare bacterial infection, including how you get it, the symptoms, how it's treated, and the tetanus vaccination.
Read about thrombophilia, a condition where the blood has an increased tendency to form clots.
Thyroiditis is the medical term for swelling (inflammation) of the thyroid gland, which can either cause unusually low or high levels of thyroid hormones in the blood.
Find out what a total iron-binding capacity (TIBC or transferrin) test measures and what high and low TIBC levels may indicate.
Find out about tongue-tie (ankyloglossia), including signs to look for, breastfeeding problems, when to get help, how it's treated, and how it affects older children and adults.
Read about the causes of toothache, when to see your dentist, and how toothache can be relieved and prevented.
Read about tooth decay (dental caries), when acids in your mouth dissolve the outer layers of your teeth.
Topical corticosteroids (steroids) are medicines that are applied directly to the skin to reduce inflammation and irritation.
Find out about the health conditions a total protein test can help diagnose. If your total protein level is too high or too low, you'll need further tests to identify the specific proteins.
Find out what toxic shock syndrome (TSS) is, what the symptoms are, how it happens and how to reduce your chances of getting it.
Read about transcutaneous electrical nerve stimulation (TENS), a method of pain relief that involves the use of a mild electrical current.
Trimethylaminuria is an uncommon genetic disorder that causes a strong body odour, usually described as like rotting fish, faeces or garbage
Information on typhus, with links to other useful resources.
Tay-Sachs disease is a very rare and usually fatal genetic disorder that causes progressive damage to the nervous system.
Read about teeth grinding (bruxism), where you rub your teeth together and clench your jaw. It's often stress or anxiety related and is treated with muscle-relaxation techniques or by using a mouth guard.
Tendonitis is the swelling of a tendon, which is a thick cord attaching a muscle to a bone. It can cause joint pain and stiffness.
Tennis elbow is a condition that causes pain around the outside of the elbow. It often occurs after strenuous overuse of the muscles and tendons of the forearm, near the elbow joint.
Lumps and swellings in the testicles are a relatively common symptom in boys and men, and can have a number of different causes.
Read about testicular cancer (cancer of the testicle), including information about symptoms, causes, diagnosis and treatment.
Read about thalassaemia, a group of blood disorders that affect a substance called haemoglobin. Find out about the symptoms, causes and treatments for the condition.
Threadworms (pinworms) are tiny worms in your poo. They're common in children and spread easily. You can treat them without seeing your GP.
Find out about the symptoms of thyroid cancer, why it happens, how it's treated, and what the outlook is.
Find out about tick-borne encephalitis (TBE), a viral infection spread to humans by the bite of a small spider-like parasite called a tick.
Tics are unintentional, fast and repetitive muscle movements. Find out how long they last, when to get medical advice and how they can be treated.
Read about tinnitus, including what problems it can cause, why it happens and how it's treated.
Tonsillitis is inflammation of the tonsils. It's usually caused by a viral infection or, less commonly, a bacterial infection.
Tourette's syndrome is a condition that causes a person to make involuntary sounds and movements called tics.
Toxocariasis is a rare infection caused by roundworm parasites. It's spread from animals to humans through contact with infected faeces.
Read about toxoplasmosis, a parasitic infection that can be dangerous for pregnant women and people with weak immune systems.
Find out what a tracheostomy is, when it's used and how it's carried out. Also, read about living with a tracheostomy and the possible risks and complications.
Find out about transient ischaemic attack (TIA) or "mini stroke", including what causes it, the symptoms, how it's diagnosed, and when to seek medical advice.
Read all about transurethral resection of the prostate (TURP), a surgical procedure used to cut away a section of the prostate gland if it's causing problems with urination.
If you're planning to travel outside the UK, you may need to be vaccinated against some of the serious diseases found in other parts of the world.
Trichomoniasis is a sexually transmitted infection (STI) caused by a tiny parasite called Trichomonas vaginalis (TV).
Trichotillomania is when someone can’t resist the urge to pull out their hair.
Find out about trigeminal neuralgia, which is sudden, severe facial pain, often described as sharp, shooting or like an electric shock.
Trigger finger is a condition that affects 1 or more of the hand's tendons, making it difficult to bend the affected finger or thumb.
Read about tuberculosis (TB), which is a curable bacterial infection spread by inhaling tiny droplets from the coughs or sneezes of an infected person.
Tuberous sclerosis, also known as tuberous sclerosis complex, is a rare genetic condition that causes mainly non-cancerous (benign) tumours to develop in different parts of the body.
Turner syndrome is a genetic disorder that only affects females. It causes a wide range of symptoms and some distinctive characteristics.
Read about type 2 diabetes, a lifelong condition that causes a person's blood sugar level to become too high.
Find out about typhoid fever, what causes it, how it's treated and what you can do to protect yourself if you're travelling to a high-risk area.
A tremor is when you're not able to control shaking or trembling in part of your body.
Temporal arteritis is a condition where medium and large arteries, usually in the head and neck, become inflamed.
Thrush is a common yeast infection that affects men and women. It's usually harmless but it can be uncomfortable and keep coming back. It is not classed as a sexually transmitted infection (STI).
Twitches are common and very rarely a sign of anything serious. They often go away on their own, but see a GP if a twitch lasts more than 2 weeks.
NHS guide to type 1 diabetes.