Conditions

The aorta is the largest blood vessel in the body: it leaves the heart, runs down through the chest into the abdomen and from there distributes blood to every…

Acanthosis nigricans is the appearance of dark, thickened, velvety patches of skin in the body's folds.

Achalasia is a disorder of the oesophagus in which the muscular ring at the junction with the stomach stops opening on cue, while the oesophagus itself loses…

A chemical burn happens when a corrosive substance reaches the skin, the eyes, the mouth or the airways.

Acne develops when a hair follicle becomes blocked with sebum and dead cells and the bacteria that normally live on the skin multiply inside it.

An acoustic neuroma is a benign tumour that grows from the sheath of the nerve responsible for hearing and balance.

Acromegaly is a rare endocrine condition in which the body produces an excess of growth hormone over a period of years.

Actinic keratosis, also called solar keratosis, describes dry rough patches of skin that develop where sunlight has been accumulating for years.

Actinomycosis is a rare, slow-burning infection caused by bacteria that live permanently in the mouth, the gut and the genital tract.

The gallbladder is a small pouch tucked under the liver that works as a holding tank: it collects bile, concentrates it and squeezes it into the gut when a…

Almost everyone has a painful lower back at some point in life. Nearly always it means neither that the spine is falling apart nor that you should take to…

Bacterial vaginosis is the most common reason for a change in vaginal discharge in women of reproductive age.

A Baker's cyst, also called a popliteal cyst, is a soft bulge in the hollow behind the knee.

Balanitis is inflammation of the head of the penis, often together with the inner surface of the foreskin.

On either side of the vaginal opening, within the outer lips, lie two small glands. Their ducts open outwards and release fluid that keeps the tissue moist.

Bed bugs are insects that feed on blood at night and hide during the day in mattress seams, bed frames, skirting boards and furniture.

Behçet's disease is a rare inflammatory condition in which the immune system attacks the walls of a person's own blood vessels for no apparent reason.

Bell's palsy is the sudden weakness of the muscles on one side of the face caused by inflammation of the facial nerve.

The bile ducts are the thin tubes that carry bile down from the liver and the gallbladder into the bowel.

Bird flu is a disease of birds caused by influenza A viruses. They are poorly suited to people: the receptors the virus latches on to in a bird's airways and…

Cancer is not one disease but a large family — more than two hundred of them — sharing a single mechanism: a cell stops obeying the body's instructions and…

The womb has two parts: the body, inside which a baby is carried, and the cervix, the narrow opening into the vagina.

Carbon monoxide forms wherever fuel burns without enough air: in a faulty water heater, in a stove whose damper was shut too early, in a barbecue carried…

Cardiomyopathy is a disease of the heart muscle itself, not of the vessels or the valves. The wall of a heart chamber stretches, thickens or loses its give…

This is not one illness but a family of conditions sharing a single stage: the heart and the arteries.

The hand goes numb at night, you wake up and shake it to bring the feeling back — that is how compression of the median nerve at the wrist usually begins.

Behind the pupil sits a clear lens. It focuses light onto the retina and changes shape as we look up from a book to the window.

Catarrh is an old word and not a very precise one. It names not a disease of its own but a state: the lining of the nose, the sinuses and the throat swells…

A cavernoma is a small tangle of abnormally built blood vessels sitting inside nervous tissue.

This is one of those conditions almost nobody has heard of until they meet it, and one worth knowing about in advance, because the clock runs in hours.

Dandruff is scale from the scalp shedding faster than normal. It is not caused by poor hygiene or by dryness, as is commonly assumed: in most cases there is…

Deafblindness is the combination, in one person, of hearing loss and sight loss. Reports and translations also call it dual sensory loss or multisensory…

Deep vein thrombosis is a blood clot in a deep vein, most often in the calf or thigh and less often in the arm.

Dehydration is not an illness in itself but a state: the body has lost more water and salt than it has taken in.

Dementia is not one illness but an umbrella term for conditions in which memory, thinking, language and the ability to manage everyday life gradually decline.

Dengue is caught in one way only, from the bite of a mosquito; it does not pass from person to person.

An abscess is a pocket of pus that bacteria have made inside a tooth, in the bone beside its root, or in the gum.

Diabetes is a group of conditions that share one feature: too much glucose in the blood. It is not a single disease.

Diabetes insipidus is an uncommon condition in which the kidneys stop holding on to water.

Ketoacidosis is where a shortage of insulin ends up when nobody notices it in time. Glucose stops reaching the cells, the body falls back on burning fat, and…

The words "my ear hurts" cover at least three different illnesses, and each is treated in its own way.

Puberty begins in girls between 8 and 13 and in boys between 9 and 14. If signs appear earlier or, conversely, do not arrive on time, it is worth having the…

Menopause arrives on average at around 51. If periods stop before 45 it is called early menopause, and before 40, premature ovarian insufficiency.

The ear does not need cleaning out. Wax is not dirt but the working lubricant of the ear canal: it is acidic, so germs do badly in it, it traps dust and it…

Ebola is a rare, severe infection whose outbreaks arise in particular districts of central and western Africa.

After fertilisation the egg has a few days to travel down the fallopian tube and settle inside the womb.

Ectropion is what happens when the lower eyelid falls away from the eyeball and turns outwards.

Edwards' syndrome is a rare genetic condition in which the cells carry an extra, third copy of chromosome 18.

Connective tissue is what holds the body together from the inside: ligaments, tendons, the walls of blood vessels, the coverings of internal organs, the deep…

Ejaculation seems a simple, automatic business right up to the day it stops working the way it should.

Anyone can fall, but past sixty a fall stops being mere clumsiness. At that age a bone breaks from standing height, and a few hours spent on the floor…

A seizure during a high temperature is one of the most frightening things a parent can be handed.

A fibroid is a firm lump of muscle and fibrous tissue that grows in the wall of the womb. It is not a tumour in the usual sense: it does not turn into cancer…

Fibromyalgia is the situation where almost everything hurts for a very long time while the tests find nothing: the blood work is clean, the scans show no…

A flat foot is one whose inner arch has dropped, so that when you stand the sole meets the floor along almost its whole length.

Flu is not a bad cold but a different infection with a different character altogether. A cold creeps up on you: the throat prickles today, the nose runs…

This name covers the whole range of effects a child is left with because their mother drank alcohol during pregnancy.

A food allergy is a mistake made by the immune system: it reads the protein in an ordinary food as a threat and answers it the way it would answer an infection.

Food intolerance is what happens when the body cannot cope with digesting a particular food, or a substance inside it.

Food poisoning is the illness caused by food contaminated with germs or with the toxins they produce.

The gallbladder is a small pouch under the liver that stores bile and releases it into the bowel when fatty food arrives.

The gallbladder is a small pouch tucked under the liver where bile is stored between meals.

A ganglion cyst is a soft, mobile little ball that turns up under the skin, most often on the wrist, on a finger or on the top of the foot.

Gangrene is the death of a part of the body inside a living organism. Tissue dies when blood, and with it oxygen, stops reaching it: with nothing to live on…

The inside of the stomach is lined with a mucous membrane that spends all day sitting in an acid strong enough to dissolve a piece of meat.

A healthy stomach does not merely store food: it grinds it down and pushes it onward into the duodenum in measured portions.

Gender dysphoria is the name not for a gender identity that fails to match the body, but for the distress that mismatch causes. The distinction matters.

Of all the sexually transmitted infections, this is the one that frightens people most, and almost always more than it deserves.

These are ordinary warts that have grown in the one place nobody wants to find them. They are caused by human papillomavirus, the same HPV that gets talked…

This is a diagnosis that almost always arrives out of the blue: a woman feels perfectly well, has no complaints at all, and then a test result tells her she…

Haemophilia is an inherited shortage of one of the proteins that turn a soft clot into a firm plug.

Haemophilus influenzae type b is a bacterium that lives quietly in the nose and throat of a proportion of perfectly healthy people.

The back of the thigh is made up of three muscles running from the sitting bone down to the bones of the lower leg, which means they work across two joints at…

This is one of the most ordinary childhood infections: ulcers in the mouth, spots and small blisters on the palms and soles, a modest temperature and a child…

The old name misleads on both counts: hay has nothing to do with it and there is no fever. This is an allergy to pollen.

You can bang your head almost anywhere: on ice, on a staircase, on the corner of an open cupboard door.

Head lice are insects that live on the scalp and feed on blood. They are very common in school-age children and have nothing to do with cleanliness — if…

Hearing leaves quietly. Almost nobody wakes up deaf one morning: what usually happens is that over the years the television creeps louder, you ask people to…

A heart attack happens when one of the arteries feeding the heart is blocked by a clot. The patch of muscle that depended on it is left without oxygen and…

The heartbeat does not start on its own. Each contraction begins with an electrical signal that arises in the upper chambers and travels down dedicated…

Ichthyosis is a group of inherited conditions in which the renewal and shedding of the outer layer of skin is disrupted.

The lung works like a sponge made of hundreds of millions of tiny air sacs called alveoli.

Impetigo is a superficial bacterial infection of the skin. It is caused by staphylococci and streptococci — bacteria that sit quite peacefully on the skin…

Indigestion is the name for a cluster of unpleasant sensations in the upper abdomen and behind the breastbone that come on while eating or shortly afterwards.

A piercing is a wound that takes weeks or months to close, and during that time infection is a real risk.

Endocarditis is inflammation of the inner lining of the heart, and it almost always settles on a valve.

Infertility is the word used when pregnancy does not happen after a year of regular sex without contraception.

Behind this name, usually shortened to IBD, sit two different illnesses: Crohn's disease and ulcerative colitis.

An ingrown hair is a hair that fails to emerge as it grows and curls back into the skin. The body treats it as a foreign body, and a red, painful bump…

An ingrown toenail is a nail edge that digs into the skin at the side of the toe. It hurts, becomes inflamed and frequently gets infected.

Japanese encephalitis is a viral infection carried by mosquitoes across Asia and the western Pacific.

Jaundice is not a disease but a sign: the skin and the whites of the eyes turn yellow when bilirubin builds up in the blood.

Most encounters with stinging sea life come down to a few hours of burning pain and a stripe of rash that fades within a week.

Jet lag is the mismatch between your body clock and local time after a fast flight across several time zones.

Hypermobility means joints that move beyond their usual range. On its own it is not an illness: a sizeable share of people have unusually loose joints…

Kawasaki disease is acute inflammation of the walls of the small and medium arteries, and it starts in childhood, most often under the age of five.

A keloid is a scar that grows more than it should and extends beyond the boundaries of the original wound.

Keratosis pilaris is the small rough bumps that give the skin a sandpaper feel or a permanent goose-pimple look.

The kidneys sit deep inside the body, one on each side of the spine beneath the lower ribs, and a tumour there can grow for a long time in silence: there is…

A kidney infection, or pyelonephritis, is an inflammation that began not in the bladder but higher up, in the kidney itself.

A kidney stone is a hard lump of crystals that grows in urine the way salt drops out of a saturated solution.

Klinefelter syndrome means one extra X chromosome in a boy: instead of the usual XY the make-up is XXY.

Knock knees, or genu valgum, describes the position in which the knees come together while the ankles stay apart with a gap between them.

A tooth that comes right out of its socket after a blow or a fall is one of the few dental emergencies where the clock really matters.

Kyphosis is the backward curve of the spine in the chest region — the one that makes the upper back look rounded.

Labial fusion, also called labial adhesions, is when a girl's inner labia stick together along the midline.

These are two closely related conditions of the inner ear in which a person suddenly loses all sense of steadiness: the room starts to spin, nausea sets in…

Lactose is the sugar in milk. To absorb it, the small intestine has to produce an enzyme called lactase, which splits it into two simple sugars.

This is an uncommon condition in which the command travelling from nerve to muscle fails to get through properly.

The larynx is the short stretch of airway between the throat and the windpipe, and the vocal cords are stretched across the inside of it.

Laryngitis means inflammation of the voice box and, in most cases, swelling of the vocal cords.

A lazy eye, or amblyopia, is when one eye sees less well than the other not because of any disease of the eye itself, but because in the earliest years of…

A cramp is a sudden, involuntary tightening of a muscle that you cannot release by willpower.

This is a severe pneumonia you catch from water rather than from another person. The bacterium Legionella multiplies in lukewarm pipework, hot water…

This is an infection caught from water, soil and animals: the leptospira bacterium is shed in the urine of rodents and livestock, reaches fresh water and damp…

A macular hole is a full-thickness defect right at the centre of the retina, in the very spot we use to read, recognise faces and pick out fine detail.

Malaria is a parasitic disease passed on by mosquitoes in the tropics and subtropics. A single bite is enough.

The skull is a closed box of fixed volume, and anything extra growing inside it sooner or later gets in the way.

A ball catches the tip of the finger, or the finger snags on a bedsheet or on a sock while getting dressed, and from that moment the last bone of the finger…

This is not only about hunger or poverty, although it is about those too. Far more often a person is eating and still getting less than the body needs…

Connective tissue is what holds the body together from the inside: the walls of arteries, the ligaments of joints, the suspension of the lens in the eye, the…

Mastitis is inflammation of the breast tissue. It is met most often by women in the first months of breastfeeding: an area of the breast turns firm, hot and…

Mastocytosis is a rare condition in which too many mast cells build up in the tissues. The body needs these cells, but when there are too many they empty…

Mastoiditis is a pus-forming infection of the bone you can feel as a small lump just behind the ear.

Measles is a viral infection that spreads more easily than almost anything else people catch.

A healthy brain keeps a firm border between sleep and wakefulness. In narcolepsy that border blurs: sleep rolls in during the day and cannot be resisted…

Behind the nose and around it lies a whole system of cavities: the nasal cavity itself and four pairs of air-filled sinuses — in the cheeks, in the forehead…

A nasal polyp is not a tumour and not a lump that sprang up out of nowhere. It is a piece of lining that has been inflamed for years, filled with fluid and…

The nasopharynx is a small space just behind the nose, above the soft palate. Air passes through it, and the tubes that ventilate the middle ear open into it.

This is a rare infection in which the microbes settle not in the skin but underneath it, in the thin sheets of tissue that wrap the muscles.

Neonatal herpes is infection of a newborn with the herpes simplex virus — the same virus that in adults causes a cold sore on the lip or sores on the genitals.

Nephrotic syndrome is the condition in which the kidneys stop holding on to protein, so that large amounts of it are lost in the urine.

NF1 is a condition you are born with, caused by a gene that normally keeps the growth of nerve sheath cells in check and no longer does its job.

NF2 is a rare inherited condition in which benign tumours grow on nerves inside the skull and the spine.

This is a rare autoimmune condition in which the immune system attacks the body's own nervous tissue — above all the optic nerves, the spinal cord and certain…

Obesity is not a cosmetic matter and not a failure of willpower. It is a state in which so much body fat has built up that it starts interfering with the…

This is a rare birth defect: the oesophagus never formed as a continuous tube. Its upper part ends in a blind pouch and does not join the stomach, while the…

The oesophagus is a muscular tube about twenty-five centimetres long that runs from the throat down to the stomach; the throat itself is a different organ…

The candida fungus lives in the mouth of roughly one healthy person in two and gives no sign of itself: saliva, the neighbouring bacteria and the immune…

Orf is a skin infection caught from sheep and goats. Medical notes call it contagious ecthyma or contagious pustular dermatitis, and people who work with…

Osteoarthritis is the commonest joint disease. It develops slowly: the cartilage covering the ends of the bones loses its springiness and thins, the bone…

Osteomyelitis is infection of the bone and the bone marrow. Bone looks impregnable, yet germs reach it by three routes: through the bloodstream, from a…

An osteophyte is a hard bony projection that grows at the rim of a joint or at the edge of a vertebra.

In osteoporosis, bone loses density and internal scaffolding: from the outside it looks the same, but inside it comes to resemble a sponge with large holes.

Otosclerosis is abnormal bone growth in the middle and inner ear that locks one of the tiny hearing bones in place so it can no longer pass sound on.

Dyshidrotic eczema is a type of eczema affecting the hands and feet, with deep blisters that itch intensely.

In Paget's disease the machinery that constantly renews bone goes wrong in a few particular bones.

Paget's disease of the nipple is a cancerous change in the skin of the nipple and areola, and behind it there is almost always a cancer inside the milk ducts.

The pancreas sits deep in the upper abdomen, behind the stomach. It produces the enzymes that digest food and hormones including insulin.

In Parkinson's disease the nerve cells in a small area of the brain that make dopamine gradually die off.

Patau's syndrome is a rare chromosomal condition in which a baby's cells carry a third copy of chromosome 13.

Pelvic inflammatory disease (PID) is an infection of the upper female genital tract: the womb, the fallopian tubes, the ovaries and the tissue around them.

Pelvic organ prolapse is when the bladder, the bowel or the womb slips downwards and pushes against the wall of the vagina, and sometimes appears outside it.

Pemphigus vulgaris is a rare autoimmune condition in which the immune system destroys the connections between cells within the upper layer of the skin and…

This is one of the rarest cancers in men. It almost always starts in the skin — a patch, a small lump or a sore on the glans or on the inner surface of the…

Q fever is an infection people catch from animals. It is caused by the bacterium Coxiella burnetii, which lives mainly in sheep, goats and cattle.

Rabies has a feature that sets it apart from other infections: while there are no symptoms it can be prevented with almost complete reliability, and once…

In the cold the fingers turn white and go numb, then turn blue, and as they warm up they flush red, tingle and hurt.

Millions of people colour their hair for years without the slightest trouble. In some, though, dye eventually provokes a reaction: from mild itching of the…

Reactive arthritis is joint inflammation that begins a few weeks after a gut or genitourinary infection.

Almost every baby brings milk back up, and almost always it means nothing at all. A newborn's stomach is tiny, the food is entirely liquid, feeds are…

RSI is not a diagnosis but a collective name for pain that comes on from monotonous work with the hands: at a keyboard, behind a counter, with a tool, with…

RSV is one of the most ordinary winter viruses, and almost every child has had it by the age of two.

The name covers every infection of the organs we breathe with: the nose and sinuses, the throat and voice box, the airways and the lungs.

In the evening, once you finally sit down or lie down, something hard to describe starts up in the legs — not quite pain, more a heavy stirring deep inside…

Being short is not, in itself, an illness. It is a feature of the body that people live with, work with, drive with, raise children with and grow old with…

Small stones made of calcium salts can build up inside the salivary glands and the ducts that drain them.

In sarcoidosis the immune system starts gathering dense clusters of cells, called granulomas, in the tissues.

Scabies is an infestation of the skin by a microscopic mite that burrows into the surface layer.

Scarlet fever is a throat infection caused by group A streptococcus, with a characteristic rash added on top.

A scar is new tissue the body makes to close a wound. It is never identical to the original skin: it has no follicles or glands and its collagen is organised…

Schistosomiasis is caused by tiny worms that live in fresh water in warm countries. There is only one way to catch it: by being in that water.

Sciatica is pain that runs from the lower back or the buttock down the leg because the sciatic nerve is irritated or compressed.

The word "scleroderma" literally means "hard skin", and it is used for two very different things.

In scoliosis the spine does not simply lean sideways: it also rotates around its own axis.

Scurvy is a severe, long-standing lack of vitamin C. Most people think of it as the sailors' disease from old books, and that is exactly why it gets missed…

The coccyx is a small bone made of several fused vertebrae at the very bottom of the spine, between the buttocks.

The temporomandibular joint links the lower jaw to the skull just in front of the ear: put your fingers there and open your mouth, and you will feel the head…

A tendon is the tough cord that ties a muscle to a bone. Every bit of force the muscle produces travels through it, which is why tendons hurt in people who…

Pain on the outside of the elbow that makes it hard to lift a mug, turn a key or shake someone's hand is nearly always the same condition.

This is the commonest headache there is: most people will have one at some point in their lives.

Testicular cancer is a tumour that grows from the tissue of the testicle itself. Among malignant tumours as a whole it is uncommon, yet in men between…

Tetanus is a severe illness in which the muscles of the whole body are gripped by painful spasms and a person can die because they stop breathing.

Thalassaemia is not one disease but a whole group of inherited conditions in which the body builds haemoglobin wrongly.

A cold is not one illness but a collective name for dozens of viruses that set up home in the nose and throat.

Between the base of the neck and the armpit there is a short, tight corridor. Through it the nerves of the brachial plexus, the subclavian artery and the…

Ulcerative colitis is long-term inflammation of the lining of the colon and rectum. For reasons that are still not fully understood, the immune system starts…

The thyroid is a small gland at the front of the neck that makes the hormones setting the pace of the whole body's metabolism.

An undescended testicle is one that is not in the scrotum because it stopped part way along the journey it should have completed before birth: in the inguinal…

Urethritis is inflammation of the urethra, the tube that carries urine out of the body. It usually announces itself with burning when you pass urine and with…

Urinary incontinence means urine leaking when you do not want it to. It is common enough to affect millions of people and awkward enough that, on average…

A UTI is an infection somewhere along the route urine takes. Most often it is the bladder, and then we are talking about cystitis; less often the infection…

Uveitis is inflammation of the uvea, the middle layer of the eye that sits between the white of the eye and the retina and supplies it with blood.

Vaginal cancer is a tumour growing in the wall of the vagina, the passage between the vulva and the neck of the womb.

Vaginismus is the involuntary tightening of the muscles around the entrance to the vagina, which makes penetration painful or impossible.

Vaginitis means inflammation of the vagina and the skin around it: itching, soreness, discharge that has changed, stinging when passing urine or during sex.

Varicose eczema is itchy, flaky, gradually darkening skin on the lower leg, most often around the ankle.

Varicose veins are swollen, twisted veins that show under the skin, usually on the calves and thighs.

Vascular dementia is a lasting decline in thinking, memory and the ability to manage everyday life, caused by parts of the brain no longer getting enough blood.

Vasculitis is not a single illness but a group of conditions sharing one mechanism: the immune system mistakenly attacks the walls of your own blood vessels.

This is an open wound on the lower leg that fails to close for weeks and months. It usually appears on the inner side of the leg, just above the ankle, and…

This page is not about feeling generally woozy. Vertigo is the sensation that you, or the room around you, is turning, tilting or drifting sideways.

Sight can vanish in a second, or it can fade so slowly that the loss is only noticed when faces on the other side of the street stop being recognisable.

Warts are caused by human papillomavirus infecting the surface layer of the skin. They are benign and, in most cases, disappear on their own: about two…

Whiplash is a neck injury caused by the head being thrown sharply back and then forward, or the other way round.

Whooping cough is a bacterial infection of the airways, spread through the air by coughing and talking, and it is extraordinarily contagious.

The heart beats on the command of an electrical signal, and that signal normally has one road to travel.

Yellow fever is a viral infection carried by mosquitoes. It exists in only two parts of the world: tropical Africa and the tropics of South and Central America.