- H. pylori infection (helicobacter pylori)
- Hair loss (alopecia)
- Hammer toes (toe deformity)
- Hand foot and mouth disease (Coxsackie virus)
- Hand fracture (broken hand)
- Hand laceration (skin cut)
- Hand swelling
- Hantavirus infection (rare, serious viral infection)
- Head injury
- Head injury in children
- Head lice
- Head trauma
- Headache
- Hearing loss
- Heart arrhythmia (abnormal heart rhythm)
- Heart attack (acute myocardial infarction, AMI)
- Heat cramps
- Heat exhaustion
- Heat rash
- Heat stroke
- Heel spur
- Hemangioma (blood vessel birthmark)
- Hematocele (collection of blood around testicle)
- Hematoma (collection of blood)
- Hemochromatosis (excess iron disorder)
- Hemolytic anemia (red blood cell destruction disorder)
- Hemolytic uremic syndrome (HUS, red blood cell destruction, kidney disease)
- Hemophilia (inherited bleeding disorder)
- Hemoptysis (coughing blood)
- Hemorrhage of pregnancy (vaginal bleeding during pregnancy)
- Hemorrhagic stroke (CVA, cerebrovascular accident)
- Hemorrhoid (enlarged rectal veins)
- Hemotympanum (blood behind ear drum)
- Henoch Schönlein purpura (blood vessel inflammation)
- Hepatic abscess (collection of pus in the liver)
- Hepatic encephalopathy (confusion from liver failure)
- Hepatitis (liver inflammation)
- Hepatitis A
- Hepatitis B
- Hepatitis C
- Hereditary hemorrhagic telangiectasia (Osler Weber Rendu syndrome)
- Hernia
- Herniated disc (slipped disc, ruptured disc)
- Herpangina (mouth blisters)
- Herpes simplex infection (viral infection)
- Herpes stomatitis (viral mouth infection)
- Herpes vulvovaginitis (viral infection of the vagina)
- Hiatal hernia (stomach pushes through diaphragm)
- Hidradenitis suppurativa (chronic collections of pus)
- High cholesterol (hypercholesteremia)
- Hip dislocation
- Hip fracture (broken hip)
- Hirschsprung disease (pediatric large intestine paralysis)
- Histoplasmosis (fungal infection)
- HIV AIDS (Human Immunodeficiency Virus, Acquired Immune Deficiency Syndrome)
- Hodgkin's disease (cancer of the lymph system)
- Hordeolum (stye of eye)
- Horner's syndrome (disruption of facial nerve function)
- Hot tub follicullitis (hair follicle infection)
- Human papillomavirus infection (HPV)
- Humerus fracture (broken upper arm)
- Huntington disease (chorea)
- Hydrocephalus (brain fluid build-up)
- Hydronephrosis
- Hyperemesis gravidarum (severe vomiting in pregnancy)
- Hyperkalemia (elevated potassium level)
- Hyperkeratosis (skin thickening)
- Hyperlipidemia (elevated blood fat level)
- Hyperosmolar hyperglycemic state (severely elevated glucose level)
- Hyperparathyroidism (elevated parathyroid hormone levels)
- Hypersensitivity pneumonitis (allergic lung disease)
- Hypertension (high blood pressure)
- Hypertensive emergency (severely high blood pressure)
- Hyperthermia (extreme heat exposure)
- Hyperthyroidism (elevated thyroid hormone)
- Hypertrophic cardiomyopathy (thickened heart muscle)
- Hyperventilation (rapid breathing)
- Hyphema (traumatic blood in eye)
- Hypocalcemia (low blood calcium)
- Hypochondriasis
- Hypoglycemia (low blood sugar)
- Hypokalemia (low blood potassium)
- Hypokalemic periodic paralysis (inherited muscle weakness and low potassium)
- Hyponatremia (low blood sodium)
- Hypoparathyroidism
- Hypotension (low blood pressure)
- Hypothermia (extreme cold exposure)
- Hypothyroidism (low thyroid hormone)
- Hypoxia (lack of oxygen)