Ataxia describes poor muscle control that causes clumsy movements. It can affect walking and balance, hand coordination, speech and swallowing, and eye movements. Ataxia usually results from damage to the part of the brain called the cerebellum or its connections. The cerebellum controls muscle coordination. Many conditions can cause ataxia, including genetic conditions, stroke, tumors, multiple sclerosis, degenerative diseases and …

Atelectasis (pronounced at-uh-LEK-tuh-sis) is the collapse of one or more parts of the lung. It specifically affects the small air sacs called alveoli. When you breathe in, your lungs fill up with air. The air travels to sacs in your lungs (alveoli), where the oxygen moves into your blood. The blood delivers the oxygen to organs and tissues throughout your …

Athlete’s foot is a common fungal infection (caused by a fungus). Athlete’s foot causes an itchy, stinging, burning rash on the skin on one or both of your feet. Athlete’s foot is most common between your toes, but it can also affect the tops of your feet, the soles of your feet and your heels. Your skin may become scaly …

Atopic dermatitis is a chronic condition that causes itchy skin that gets dry and scaly. It tends to come and go and may only be in childhood or may affect you your entire life. In people with light-colored skin, atopic dermatitis looks like red rashes. People with darker skin may develop brown, purple or gray rashes. Atopic dermatitis vs eczema: …

Atrial flutter is a common type of supraventricular arrhythmia. This means it’s an abnormal heart rhythm that starts in the upper chambers of your heart. With atrial flutter, your heart beats in a fast but consistent pattern. Faulty electrical signals cause this to happen. A normal heart rate is 60 to 100 beats a minute when you’re at rest. Atrial flutter can make your heart’s upper …

Ascariasis is an infection in your intestines caused by a roundworm called Ascaris lumbricoides (A. lumbricoides). Like other parasites, these worms use the body of a host (like a human) to mature into egg-laying adults. The more the worms thrive, the more harm they can cause the host. A. lumbricoides is a kind of soil-transmitted helminth (STH). The worms living in someone’s gut lay eggs …

An atrial septal defect (ASD) is a hole in the atrial septum, which is the wall that separates your heart’s two upper chambers (atria). An ASD is a congenital heart defect (something you’re born with) that happens when the septum doesn’t form properly. It’s also called a “hole in the heart.” An ASD allows an abnormal shunt, meaning an abnormal passageway for blood that …

Aspergillosis is a term for an infection caused by several types of Aspergillus fungi (plural of fungus). Aspergillus is usually found outdoors, in dead leaves, plants, soil or compost. It’s occasionally found in moist environments indoors. Most people breathe in Aspergillus spores every day without getting sick. But in certain people, Aspergillus can cause allergic reactions, chronic lung conditions and invasive disease that spreads to your brain, kidneys, lungs …

Asthma, also called bronchial asthma, is a disease that affects your lungs. It’s a chronic (ongoing) condition, meaning it doesn’t go away and needs ongoing medical management. Asthma affects more than 25 million people in the U.S. currently. This total includes more than 5 million children. Asthma can be life-threatening if you don’t get treatment. What is an asthma attack? …