Gamma globulin
A blood product containing antibodies, including antibodies to various bacteria and viruses; used to prevent certain infectious diseases such as hepatitis and measles, and to treat other conditions including Kawasaki disease and immune deficiency states.

Gangrene
Death and decomposition of tissue as a result of poor blood supply; often caused by infection, but also can be caused by frostbite.

Gastroenteritis
Inflammation of the lining of the stomach and intestines; can lead to stomach pain, vomiting, diarrhea and, in some cases, fever; typically caused by viral infection, but also can be caused by bacterial or parasitic infection, or by a variety of other factors.

Gastroesophageal reflux
Regurgitation of stomach contents into the esophagus; can lead to heartburn, vomiting and aspiration of stomach contents into the lungs.

Giardia
A parasitic organism (Giardia lamblia) that causes an intestinal infection marked by diarrhea and/or abdominal pain and weight loss (giardiasis); usually acquired from contaminated food or drinking water.

Glaucoma
Abnormally increased pressure within the eyeball; can cause damage to the optic nerve; if untreated, can lead to blindness.

Gynecomastia
Excessive development of the male breasts; a mild form which resolves by itself is often seen in adolescents.

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Haemophilus influenzae
Bacteria that are capable of causing a variety of infections in young children ranging from mild (conjunctivitis and ear infection) to life-threatening (sepsis and meningitis); serious infections have become much less common in some parts of the world, including North America, because of infant immunization against one type of this organism, Haemophilus influenzae type b or Hib.

Hay fever
An allergic syndrome characterized by congestion, runny nose, sneezing and watery eyes; recurs the same time every year; often caused by a sensitivity to pollen.

Heart murmur
A whooshing sound made by blood as it flows through the heart; commonly heard in normal, healthy people, but may be caused by an abnormality in the structure of the heart.

Heat stroke
Severe illness resulting from exposure to excessively high temperatures; marked by headache, confusion and/or slightly warm skin; serious cases result in collapse, coma, and very high body temperatures and heart rate; usually caused by excessive exertion in hot weather.

Hemangioma
An abnormal cluster of blood vessels, usually present at birth; can be found anywhere on the body, but most commonly in the skin; often will increase in size during the first year of life; depending on size and/or location, may require treatment, but most resolve on their own by age 4 to 5 years.

Hematocrit
The percentage of the blood occupied by cells (mostly red blood cells); in anemia, the hematocrit is low.

Hematuria
Blood in the urine originating from anywhere in the urinary tract, including the kidneys or bladder; may be detectible by laboratory tests even when not visible to the naked eye.

Hemoglobin
An iron-containing protein within red blood cells; carries oxygen from the lungs to the tissues.

Hemophilia
A set of hereditary diseases almost always seen in boys; marked by the inability to effectively clot the blood and a permanent tendency to bleed excessively.

Hemoptysis
Coughing or spitting up blood from the lungs.

Hemorrhage
To bleed; commonly used to describe profuse bleeding.

Hemorrhoids
Swollen enlarged veins in the rectum causing pain, itching, and occasional bleeding.

Hepatitis
Inflammation of the liver, usually caused by a viral infection, or a chemical or drug that is toxic to the liver; may result in jaundice, nausea, lack of appetite, weakness, fever, abdominal pain and/or vomiting.

Hepatitis A
A vaccine-preventable virus causing hepatitis that almost always goes away without treatment; usually transmitted from person to person by exposure to infected stool; prevented by hepatitis A vaccine which is required in some states.

Hepatitis B
A vaccine-preventable virus causing hepatitis that can range from very mild to fatal; chronic hepatitis B infection is more common following infection in infants than adults, and can lead to liver failure or cancer in later life; usually transmitted through blood or body fluids; readily prevented by routine immunization beginning in infancy (hepatitis B vaccine).

Hepatomegaly
An enlarged liver.

Hernia
The protrusion of a structure through an abnormal opening in the tissues which usually contain it; typically seen in the navel area (umbilical hernia) or in the groin (inguinal hernia).

Hip dislocation
Displacement of the top of the femur (thigh bone) from its normal location in the hip joint; occurs when the femur does not fit into the joint properly and/or securely; may be present at birth but usually develops after birth; can lead to serious hip problems if not treated.

Hirsute
Excessively hairy.

HIV
Human immunodeficiency virus; the causative agent of AIDS.

Hives
Urticaria; a short-lived skin rash characterized by itchy red, pink or white welts of various sizes, often with a pale area in the middle; may be triggered by factors including infection, stress, or allergy to food or drugs.

Hydrocele
A collection of fluid around the testicles that causes swelling of the scrotum; usually resolves spontaneously.

Hydrocephalus
An abnormal accumulation of fluid in specific areas (ventricles) of the brain; when left untreated, can cause increased pressure within the skull and destruction of brain tissue; sometimes treated by using a piece of tubing (a shunt) to drain the fluid from the brain to the abdomen or chest.

Hypertension
Abnormally high blood pressure.

Hyperthyroidism
Uncontrolled or excessive secretion of thyroid hormone by the thyroid gland, typically resulting in fast heart rate and breathing rate, weight loss, shakiness, irritability, hyperactivity, and/or bulging of the eyeballs (exophthalmos); effective treatment is available.

Hypospadias
A congenital abnormality of the penis in which the opening of the urinary tract (urethra) is found along the underside of the penis, or even below the penis, instead of at the tip; may require surgical repair.

Hypothyroidism
Abnormally low production of thyroid hormone by the thyroid gland causing a tendency to weight gain, poor muscle tone, constipation and low energy level; can cause severe brain damage in infants if left untreated; screening at birth allows this condition to be identified and treated before damage occurs.

Hypotonia
Abnormally low muscle tension (tone) or activity when at rest; infants with poor muscle tone are sometimes referred to as "floppy babies".

Hypoxia
Decreased amount of oxygen in the blood or body tissues.

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Impetigo
A contagious bacterial infection of the skin marked by small fluid filled blisters which break and form yellow or "honey-colored" crusts; usually caused by staphylococci or streptococci.

Inflammation
The body's response to injury, irritation or infection; a complicated process marked by pain or tenderness, warmth, redness, and swelling.

Influenza
The "flu"; illness marked by high fever, chills, extreme weakness, muscle aches, headache and cough; commonly occurring in epidemics; caused by influenza viruses; preventable by influenza vaccine.

Ischemia
Insufficient flow of blood to a localized area of tissue.

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Jaundice
Yellowish coloring of the skin, mucous membranes and whites of the eyes; caused by an excess of bilirubin in the blood.