Diseases & Symptoms

Abdominal pain is a symptom felt between the lower chest and pelvis, with causes ranging from digestive, urinary, reproductive, and vascular problems to structures outside the abdomen.

Acne (acne vulgaris) is a common chronic inflammatory disease of the pilosebaceous unit, most visible on the face, back and chest.

An IgE-mediated inflammation of the nasal lining triggered by inhaled allergens, causing sneezing, congestion, and itching; also called hay fever.

Allergy is an immune-mediated reaction to a substance that is ordinarily harmless, producing symptoms ranging from localized irritation to life-threatening anaphylaxis.

Alzheimer's disease is a progressive neurodegenerative disorder and the leading cause of dementia, marked by memory loss early on, with no cure but some drugs that slow early progression.

A rapid-onset systemic hypersensitivity reaction that can cause life-threatening respiratory or circulatory compromise.

Anemia is a reduction in blood hemoglobin that limits oxygen transport and may result from blood loss, impaired red-cell production, or excessive red-cell destruction.

An aneurysm is an abnormal localized widening of a blood vessel, usually an artery, that may cause bleeding, compression, or impaired circulation.

A group of mental disorders marked by excessive fear or worry that impairs daily functioning; this entry covers their classification, types, causes, epidemiology, diagnosis and treatment.

Aphasia is an acquired neurological impairment of language comprehension and production, most commonly resulting from focal brain injury such as stroke.

A rare bone marrow failure disorder causing reduced blood cell production, with risks of infection, bleeding, and anemia.

Appendicitis is acute inflammation of the vermiform appendix, usually caused by luminal obstruction, and it is one of the most common surgical emergencies worldwide.

A chronic inflammatory airway disease marked by variable airflow obstruction, wheezing and breathlessness, affecting hundreds of millions of people worldwide.

Atherosclerosis is a chronic inflammatory disease in which lipid-rich plaques build up in the arterial wall, and it is the leading underlying cause of heart attacks and strokes.

Atrial fibrillation is the most common sustained cardiac arrhythmia, marked by disorganized atrial electrical activity that raises the risk of stroke and heart failure.

A lifelong neurodevelopmental condition defined by differences in social communication and by restricted, repetitive behaviors.

An autoimmune disease results from immune responses against the body’s own tissues, causing damage or impaired function in one or more organs.

Autoimmunity is immune recognition of the body’s own constituents, which can cause disease when it produces tissue damage or impaired function.

Back pain is pain in the back arising from varied or unidentified causes, ranging from short-lived discomfort to persistent symptoms and disability.

Benign prostatic hyperplasia is a non-malignant enlargement of the prostate, common in older men, that becomes clinically important when it narrows the urethra or affects bladder function.

A chronic mood disorder marked by alternating episodes of mania or hypomania and depression, usually managed with long-term medication and psychological support.

Breast cancer is a malignant growth of breast cells, the most common cancer in women worldwide, with major variation in subtype, treatment and outcome.

Cancer is a group of diseases characterized by uncontrolled growth of abnormal cells, invasion of surrounding tissues, and potential spread to distant organs.

Cardiomegaly is enlargement of the heart, usually identified by imaging, that may reflect structural disease, increased workload, or physiological adaptation.

Cardiovascular disease covers disorders of the heart and blood vessels, including coronary heart disease, stroke, and peripheral arterial disease. It is the leading global cause of death.

A clouding of the eye's crystalline lens that blurs vision. It is the leading cause of blindness worldwide and is most often treated by surgical lens replacement.

Chest pain is discomfort felt in the front of the thorax. It is a symptom with many possible causes, from life-threatening cardiac, vascular and pulmonary conditions to musculoskeletal and digestive ones.

Chickenpox is a highly contagious viral infection characterized by an itchy rash and preventable through vaccination.

Cholera is an acute diarrhoeal disease caused by Vibrio cholerae that can kill within hours without treatment, and it remains a major public-health threat.

A long-term disorder of kidney structure or function, most often caused by diabetes or hypertension, that can progress to kidney failure.

Pain that persists or recurs beyond three months, shaped by biological, psychological and social factors and often a condition in its own right.

Cirrhosis is the advanced stage of chronic liver disease, marked by fibrosis and regenerative nodules that can cause portal hypertension, liver failure and liver cancer.

Colorectal cancer is a malignancy of the colon or rectum that usually arises from precancerous adenomatous polyps. It is a leading cause of cancer death worldwide and is largely preventable through screening.

An acute, usually self-limiting viral infection of the upper respiratory tract, most often caused by rhinoviruses.

Inflammation of the conjunctiva, the mucous membrane covering the white of the eye and the inner eyelids, caused by infection, allergy, or irritants.

Constipation is a pattern of infrequent, difficult, or incomplete bowel movements, often involving hard stools and arising from several possible causes.

Coronary artery disease is a condition in which atherosclerotic plaque narrows the coronary arteries and reduces blood flow to the heart muscle, and it remains a leading cause of death worldwide.

A cough is a forceful expulsion of air from the lungs, produced by a reflex that protects the airways, and it is among the most common reasons for seeking medical care.

COVID-19 is an infectious respiratory disease caused by the SARS-CoV-2 coronavirus. It emerged in late 2019 and became a global pandemic.

Dehydration is a deficit of body water caused by insufficient fluid intake, excessive fluid loss, or both, with effects ranging from thirst to life-threatening circulatory and neurological disturbances.

Dementia is a group of chronic or progressive brain disorders that impair memory, thinking and daily functioning beyond normal ageing. Alzheimer's disease is its most common cause.

Dengue fever is a mosquito-borne viral disease caused by four related dengue virus serotypes, spread mainly by Aedes mosquitoes and found across tropical and subtropical regions.

Dental caries is a biofilm-driven, diet-modulated disease in which bacterial acids demineralize tooth enamel and dentin, and it is the most prevalent chronic condition in the world.

A depressive disorder affecting mood, cognition, physical functioning, and daily life, with interacting biological, psychological, and social influences.

Diabetes mellitus is a group of metabolic diseases characterized by persistently elevated blood glucose resulting from impaired insulin production or action.

Diabetic ketoacidosis is an acute complication of diabetes involving excessive ketone production, metabolic acidosis, and fluid and electrolyte disturbances.

A condition of frequent loose or watery stools, a leading cause of illness and death in young children, mostly from infection and largely preventable and treatable.

A disease is a disturbance of normal bodily or mental functioning, identified through clinical features, biological changes, or established diagnostic criteria.

Dizziness is a nonspecific term for an unpleasant sense of imbalance, disorientation or faintness, with causes ranging from inner-ear disorders to heart problems.

A genetic condition caused mainly by an extra copy of chromosome 21 (trisomy 21), associated with intellectual disability and characteristic physical features.

A group of serious psychiatric conditions defined by disturbed eating, weight- and shape-related concerns, and significant impacts on physical health and daily functioning.

Eczema is a group of chronic or recurrent inflammatory skin conditions marked by itch, redness, and a weakened skin barrier.

Edema is the swelling of body tissues caused by abnormal fluid buildup between cells, a clinical sign with many possible causes, including heart, kidney, and liver disease.

Embolism is obstruction of a blood vessel by material carried through the circulation from another site.

A chronic, estrogen-dependent inflammatory condition in which endometrial-like tissue grows outside the uterus, causing pelvic pain and often infertility.

Epilepsy is a chronic neurological disorder marked by recurrent, unprovoked seizures caused by abnormal, excessive firing of neurons in the brain.

Erectile dysfunction is persistent difficulty achieving or maintaining a penile erection sufficient for satisfactory sexual activity.

Fatigue is a subjective, persistent sense of low energy and reduced drive, physical, mental or both, which may reflect normal exertion or an underlying condition.

Fatty liver disease is excess fat stored in liver cells, now classed as steatotic liver disease; it ranges from simple steatosis to scarring, cirrhosis and liver cancer.

Fever is an elevation of core body temperature above its regulated set point, usually triggered by infection or inflammation through prostaglandin E2 signaling in the hypothalamus.