Teen health
Learning Center
Hemangioma
This red mark on a baby's skin looks like a rubbery bump or flat red mark and is made up of extra blood vessels in the skin. It generally goes away by age 10. Learn more about its causes and treatment.
Hematocrit test
Learn about this red blood cell blood test, including why it's used and what to expect.
Hemophilia
In this inherited disorder, the blood lacks one of several clot-forming proteins. The result is prolonged bleeding, which can be life-threatening.
Hepatitis A
This contagious liver infection is caused by a virus. Learn more about its symptoms, treatment and prevention, including the hepatitis A vaccine.
Hepatitis B
This highly contagious virus can cause long-lasting problems if it goes untreated. Learn about the symptoms, treatment and prevention of this serious liver infection.
Hip dysplasia
In infancy, this condition often can be corrected with a soft brace. Older children and young adults might require surgery to correct the misalignment.
Hirschsprung's disease
This digestive disorder that's present at birth affects the nerves in the colon. It causes severe constipation but can be treated.
Hodgkin's vs. non-Hodgkin's lymphoma: What's the difference?
Learn how types of lymphomas are determined using lab tests to examine cancer cells.
Holter monitor
This wearable device keeps track of the heart's rhythm during daily activities. Learn when you might need one and what to expect.
Horner syndrome
Find out about Horner syndrome, an interruption in nerve signals from the brain to the eye and face on one side of the body.
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