This mental health condition causes extreme mood swings that include emotional highs, called mania, and lows, known as depression.
Disease
Bird flu (avian influenza)
Flu viruses in other animals, such as birds, may be a risk to people. Learn more about the symptoms, causes, prevention and treatment for bird flu in people.
Disease
Black hairy tongue
This condition gives the tongue a dark, furry look. It results from a buildup of dead skin cells on the many tiny, rounded bumps on the tongue's surface.
Disease
Bladder cancer
Blood in the urine (hematuria) sometimes is a sign of bladder cancer. Learn about other bladder cancer signs and symptoms and explore treatment options.
Disease
Bladder exstrophy
This rare condition present at birth happens when the bladder develops outside of an unborn baby during pregnancy. The condition can be repaired with surgery.
Disease
Bladder stones
Minerals in your urine can crystallize if you have trouble emptying your bladder completely, creating this potentially painful condition.
Disease
Blastocystis hominis
This microscopic organism is a parasite that can live in your digestive system. Whether it causes digestive problems isn't clear.
Disease
Blepharitis
This often chronic eyelid condition can be difficult to treat. It might be uncomfortable, but it doesn't usually damage eyesight and isn't contagious.
Disease
Blocked tear duct
Watery, irritated eyes may occur when your tears can't drain normally. Learn about this common eye condition that affects newborns and sometimes, adults.
Disease
Blood in urine (hematuria)
Lots of things can cause bloody urine. Some are serious problems, and others are harmless. Find out why it's always important to get a checkup.
Disease
Body dysmorphic disorder
This mental disorder causes persistent, intense focus, shame and anxiety over perceived body defects, often resulting in many cosmetic procedures as a fix.
Disease
Body lice
Body lice are tiny insects that live in your clothing and feed on your blood. Find out how to treat and prevent this itchy nuisance of a bug.