Health A to Z

This is a comprehensive encyclopedia of over 500 conditions and diseases, with over 800 illustrations. Created by the faculty at Harvard Medical School, entries offer an overview of the condition along with a description of symptoms, diagnosis, tips for prevention, treatment options, prognosis, and advice about when to call a professional.

Abdominal Adhesions
Abdominal Aortic Aneurysm
Absence Seizures (Petit Mal Seizures)
Achalasia
ACL (Anterior Cruciate Ligament) Injuries
Acne
Acoustic Neuroma
Acute Bronchitis
Acute Lymphocytic Leukemia (ALL) in Adults
Acute Lymphocytic Leukemia (ALL) in Children
Acute Myeloid Leukemia (AML)
Acute Pancreatitis
Acute Prostatitis
Acute Sinusitis
Adenocarcinoma of the lung
Adrenocortical Carcinoma
Age Spots (Solar Lentigo, Liver Spots)
Aging Overview
Alcohol Use Disorder (Alcoholism)
Alcohol Withdrawal
Allergy Overview
Allergy Shots (Allergen Immunotherapy)
Alopecia Areata
Altitude Sickness
Alzheimer's Disease
Amenorrhea
Amyloidosis
Amyotrophic Lateral Sclerosis (ALS)
Anal Cancer
Anal Disorders
Anal Itch (Pruritus Ani)
Anaphylaxis
Anemia Overview
Angina
Ankle Fracture
Ankle Sprain
Ankylosing Spondylitis
Anorexia Nervosa
Antibiotic-Associated Diarrhea
Antiphospholipid Antibody Syndrome
Antisocial Personality Disorder
Aplastic Anemia
Appendicitis
Arm Fracture
Arthritis Associated With Inflammatory Bowel Disease
Asthma
Astigmatism
Asymptomatic Bacteriuria
Atherosclerosis
Athlete's Foot (Tinea Pedis)
Atrial Fibrillation
Attention-Deficit Hyperactivity Disorder (ADHD)
Autism (Autism Spectrum Disorder)
Back Pain
Bacterial Vaginosis (Gardnerella Vaginitis)
Balanitis
Barium Enema
Barotrauma
Bartholin's Gland Cyst
Basal Cell Carcinoma
Bedsores (Decubitus Ulcers)
Bedwetting (Enuresis)
Behcet's Disease
Bells Palsy
Bile Duct Diseases
Biliary Colic
Bipolar Disorder (Manic Depressive Illness or Manic Depression)
Black Eye
Bladder Cancer
Bladder Infection (Cystitis)
Blepharitis
Blisters (Overview)
Body Lice
Boils and Carbuncles
Borderline Personality Disorder
Botulism
Bowel Obstruction
Bradycardia
Brain Abscess
Brain Tumor Overview
Breast Cancer
Broken Jaw
Broken Nose (Nasal Fracture)
Bulimia
Bunion
Bursitis
Campylobacteriosis
Cancer Overview
Candidiasis
Carbon Monoxide Poisoning
Carcinoid Tumors of the Lung
Cardiac Arrhythmias
Cardiomyopathy
Carpal Tunnel Syndrome
Cataracts
Celiac Disease (Non-Tropical Sprue)
Cellulitis
Cerebral Palsy
Cervical Cancer
Cervical Polyps
Cervicitis
Chemical Injury to the Eye
Chickenpox (Varicella)
Chlamydia
Cholecystitis
Chondromalacia
Chondrosarcoma
Chorionic Villus Sampling
Choroidal Melanoma
Chronic Fatigue Syndrome
Chronic Hepatitis
Chronic Laryngitis
Chronic Lymphocytic Leukemia (CLL)
Chronic Obstructive Pulmonary Disease (COPD)
Chronic Otitis Media, Cholesteatoma and Mastoiditis
Chronic Pancreatitis
Chronic Prostatitis
Chronic Sinusitis (in Adults)
Cirrhosis
Cluster Headache
Cogan's Syndrome
Collarbone (Clavicle) Fracture
Colon Polyps
Colorectal Cancer
Coma and Persistent Vegetative State
Common Cold (Viral Rhinitis)
Complex Regional Pain Syndrome (CRPS)
Concussion
Constipation and Impaction
Contact Dermatitis
Conversion Disorder (Functional Neurological Symptom Disorder)
Corneal Abrasion
Corns and Calluses
Coronary Artery Disease
Creutzfeldt-Jakob Disease (CJD)
Crohn's Disease
Crossed Eyes (Strabismus)
Croup
Curvature of the Penis (Peyronie's Disease)
Cystic Fibrosis
Cysts (Overview)
Cytomegalovirus (CMV)
Dandruff
Decompression Sickness
Delusional Disorder
Dementia
Depression Overview
Dermatofibroma
Detached Retina
Developmental Dysplasia of the Hip
Deviated Septum
Diabetes Mellitus Overview
Diabetic Ketoacidosis
Diabetic Nephropathy
Diabetic Neuropathies
Diarrhea
Dislocated Lens
Diverticulosis and Diverticulitis
Double Vision (Diplopia)
Down Syndrome
Drooping Eyelid (Ptosis)
Dry Eye Syndrome
Dry Skin
Dysfunctional Uterine Bleeding
Dyslexia
Dysthymia
Dysuria
Earache
Eczema
Edema
Emphysema
Encephalitis
Encopresis (Fecal Soiling)
End-Stage Renal Disease
Endocarditis
Endometriosis
Endophthalmitis
Enlarged Prostate (Benign Prostatic Hyperplasia)
Epidemic Pleurodynia
Epidermoid Cyst
Epididymitis And Orchitis
Epiglottitis
Epilepsy
Esophageal Cancer
Esophageal Rings And Webs
Esophageal Varices
Esophagitis
Essential Tremor
Ewing's Sarcoma
Extragonadal Germ Cell Tumors
Eye Socket Fracture (Fracture Of The Orbit)
Fallen Arch
Fallopian Tube Cancer
Familial Dysautonomia
Farsightedness (Hyperopia)
Febrile Seizures
Fecal Incontinence
Felon
Female Infertility
Fever
Fibroids
Fibromyalgia
Fifth Disease (Erythema Infectiosum)
Finger Dislocation
Flu (Influenza)
Food Allergy
Food Poisoning
Foot Sprain
Foot Ulcers
Foreign Body In Eye
Foreign Objects In The Ear
Fragile X Syndrome
Friction Blisters
Friedreich's Ataxia
Gallbladder and bile duct cancer
Gallstones
Gas (Flatulence)
Gastritis
Gastroenteritis In Adults
Gastroenteritis In Children
Gastroesophageal Reflux Disease (GERD)
Gastrointestinal Amebiasis
Gaucher Disease
Generalized Anxiety Disorder
Generalized Seizures (Grand Mal Seizures)
Genital Herpes
Genital Warts
Gestational Diabetes
Giant Cell Arteritis (Temporal Arteritis)
Giardiasis
Glaucoma
Glioblastoma Multiforme
Glomerulonephritis
Gonorrhea
Gout
Granulomatosis with polyangiitis
Graves' Disease
Graves' Eye Disease (Graves' Ophthalmopathy)
Guillain-Barre Syndrome
Hair Loss
Hammertoe
Hay Fever (Allergic Rhinitis)
Head and Neck Cancer
Head Injury In Adults
Head Injury In Children
Head Lice
Headache Overview
Hearing Loss in Adults
Hearing Loss in Children
Heart Attack (Myocardial Infarction)
Heart Failure
Heart Murmur
Heart Valve Problems
Heart Valve Replacement
Heat Stroke (Hyperthermia)
Heel Pain
Hematuria
Hemochromatosis
Hemophilia
Hemorrhagic Stroke
Hemorrhoids
Hepatitis A
Hepatitis B
Hepatitis C
Hepatitis Overview
Hereditary-Patterned Baldness
Hernia
Hernia Repair
Herniated Disk
Hiatal Hernia
High Blood Pressure (Hypertension)
High Cholesterol (Hypercholesterolemia)
Hip Fracture
Hirsutism
HIV/AIDS
Hives (Urticaria)
Hodgkin Lymphoma
Hot Flashes
Human Papilloma Virus (HPV)
Huntington's Disease (Chorea)
Hydrocephalus
Hyperkeratosis
Hyperthyroidism
Hypoglycemia
Hypoparathyroidism
Hypothyroidism
Ichthyosis
Illness Anxiety Disorder
Immune Thrombocytopenic Purpura (ITP)
Impetigo
Impotence (Erectile Dysfunction)
Infectious Arthritis
Infectious Mononucleosis
Ingrown Toenail
Inguinal Hernia
Insomnia
Interstitial Cystitis
Intracranial Aneurysms
Iron Deficiency
Irritable Bowel Syndrome (IBS)
Jet Lag
Jock Itch (Tinea Cruris)
Juvenile Arthritis
Kaposi's Sarcoma
Kawasaki Syndrome
Keloids
Keratitis
Kidney Cancer
Kidney Failure
Kidney Stones
Knee Sprain
Lactose Intolerance
Lacunar Stroke
Langerhans' Cell Histiocytosis (Histiocytosis X)
Laryngitis
Latex Allergy
Lazy Eye (Amblyopia)
Lead Poisoning
Leg Fracture
Leg Strain
Leukemia (Overview)
Liver Cancer
Long QT Syndrome
Lung Cancer Overview
Lupus (Systemic Lupus Erythematosus)
Lyme Disease
Lymphedema
Lymphoma Overview
Macular Degeneration
Major Depression
Malaria
Male Infertility
Malignant Hyperthermia
Marfan Syndrome
Maturity Onset Diabetes of the Young (MODY)
Measles (Rubeola)
Meckel's Diverticulum
Medication Allergy
Melanoma
Melasma (Chloasma)
Meniere's Disease
Meningitis
Menopause And Perimenopause
Mesothelioma
Metastatic Brain Tumors
Mid-Menstrual Cycle Pain (Mittelschmerz)
Middle-Ear Infection (Otitis Media)
Migraine
Miscarriage
Mitral Valve Prolapse
Molar Pregnancy
Moles (Nevi)
Molluscum Contagiosum
Morton's Neuroma
MRSA Skin Infection
Multiple Myeloma
Multiple Sclerosis
Mumps
Muscle Strain
Muscular Dystrophy
Myasthenia Gravis
Myelodysplastic Syndromes
Myocarditis
Myositis
Nabothian Cysts
Nail Trauma
Narcolepsy
Nasal Polyps
Nausea
Nearsightedness (Myopia)
Nephrectomy
Neuroblastoma
Neurofibromatosis
Non-Hodgkin Lymphoma
Non-Small Cell Lung Cancer
Nosebleed (Epistaxis)
Obesity
Obsessive-Compulsive Disorder (OCD)
Onycholysis
Optic Nerve Swelling (Papilledema)
Oral Cancer
Osgood-Schlatter Disease
Osteoarthritis
Osteoporosis
Osteosarcoma
Ovarian Cancer
Paget's Disease of Bone
Pain
Painful Sexual Intercourse (Dyspareunia)
Pancreatic Cancer
Pancreatitis Overview
Panic Disorders
Parathyroid Cancer
Parkinson's Disease
Paronychia
Partial Seizures (Focal Seizures)
Pelvic Inflammatory Disease (PID)
Peptic Ulcer
Perforated Eardrum
Pericarditis
Peripheral Arterial Disease
Peritonsillar Abscess
Pertussis (Whooping Cough)
Phenylketonuria (PKU)
Phimosis and Paraphimosis
Phobia
Pinkeye (Conjunctivitis)
Pituitary Tumors
Pityriasis Rosea
Plague (Yersinia Pestis)
Plantar Fasciitis
Pleurisy And Pleural Effusion
Pneumoconiosis
Pneumonia
Pneumothorax
Polio
Polyarteritis Nodosa
Polychondritis
Polycystic Kidney Disease
Polycystic Ovary Syndrome
Polymyalgia Rheumatica
Post-Polio Syndrome
Post-Traumatic Stress Disorder
Posterior Cruciate Ligament (PCL) Injuries
Postpartum Depression
Pre-Diabetes
Preeclampsia And Eclampsia
Premature Ejaculation
Premenstrual Syndrome (PMS)
Presbyopia
Priapism
Prostate Cancer
Pseudogout (CPPD)
Psoriasis
Psoriatic Arthritis
Pubic Lice Or Crab Lice
Pyelonephritis
Rash
Raynaud's Phenomenon
Reactive Arthritis
Rectocele
Respiratory Syncytial Virus
Restless Legs Syndrome
Retinal Vessel Occlusion
Retinitis Pigmentosa
Retinoblastoma
Retinopathy
Retrobulbar Neuritis
Retrograde Ejaculation
Reye Syndrome
Rhabdomyosarcoma
Rheumatoid Arthritis
Ringworm (Tinea)
Rocky Mountain Spotted Fever
Rosacea
Rotator Cuff Injury
Salivary Gland Disorders
Sarcoidosis
Scabies
Scarlet Fever
Schizophrenia
Schizotypal Personality Disorder
Sciatica
Scleritis
Scleroderma
Scoliosis
Screening for Birth Defects in Early Pregnancy (Combined Test, Integrated Test, and Quadruple Test)
Sebaceous Cysts
Seborrheic Dermatitis
Seborrheic Keratoses
Secondary Hypertension
Sedative, Hypnotic or Anxiolytic Drug Use Disorder
Seizure Overview
Sexually Transmitted Diseases (Overview)
Shigellosis
Shin Splints
Shingles (Herpes Zoster)
Shoulder Dislocation
Shoulder Sprain
Sick Sinus Syndrome
Sickle Cell Anemia
Sjogren's Syndrome
Skin Tags (Acrochordon)
Sleep Apnea
Sleepwalking and Sleep Terrors
Small Cell Lung Cancer
Smallpox
Soft Tissue Sarcoma
Somatic Symptom Disorder
Sore Throat (Pharyngitis)
Spider Veins
Spina Bifida
Spinal Cord Trauma
Spinal Cord Tumors
Sprain (Overview)
Squamous Cell Carcinoma of the Lung
Squamous Cell Carcinoma of the Skin
Stomach Cancer
Stroke Overview
Stuttering
Styes And Chalazions
Subarachnoid Hemorrhage
Subdural Hematoma
Sun Allergy (Photosensitivity)
Sun-Damaged Skin
Superficial Thrombophlebitis
Swallowed Object
Swimmer's Ear (Otitis Externa)
Syphilis
Tachycardia
Takayasu's Arteritis
Tay-Sachs Disease
Tear Duct Infection (Dacryocystitis)
Telogen Effluvium
Tendonitis
Tennis Elbow (Lateral Epicondylitis)
Tension Headache
Testicular Cancer
Testicular Torsion
Tetanus
Throat Cancer (Larynx and Pharynx)
Thrombocytopenia
Thromboembolism (Deep Vein Thrombosis and Pulmonary Embolism)
Thrombotic Stroke
Thyroid Cancer
Tick Bites
Tics
Tinea Versicolor
Tinnitus
Toenail Fungus (Onychomycosis)
Torn Meniscus
Torsional Deformity
Tourette Syndrome
Toxic Shock Syndrome
Toxoplasmosis
Transient Ischemic Attack (TIA)
Traumatic Dislocation of the Hip
Traveler's Diarrhea
Trichomoniasis
Trigeminal Neuralgia (Tic Douloureux)
Tropical Sprue
Tuberculosis
Type 1 Diabetes Mellitus
Type 2 Diabetes Mellitus
Ulcerative Colitis
Undescended Testicle
Urethritis
Urinalysis
Urinary Health
Urinary Incontinence
Urinary Tract Infection in Men
Urinary Tract Infection in Women
Uterine And Bladder Prolapse
Uterine Cancer
Uveitis
Vaginal Atrophy (Atrophic Vaginitis)
Vaginal Cancer
Vaginal Discharge
Vaginal Yeast Infection
Vaginitis
Varicose Veins
Vascular Birthmarks
Vasculitis Overview
Vertigo
Vitamin B12 Deficiency
Vitiligo
Vocal Cord Disorders
Vulvar Cancer
Waldenström Macroglobulinemia
Warts
Wax Blockage Of The Ear Canal
Wilms' Tumor
Wrist Sprain
Yaws

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As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles. No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.