Diseases and Conditions

Find doctor-approved information about symptoms, causes, diagnosis, treatment and prevention of common diseases and conditions.

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All conditions that start with the letter O
  • Floor scale with tape measure wrapped around apple to illustrate obesity


    Obesity is a complex, and increasingly common disease that is associated with many health risks such as high blood pressure,…

  • Person washing their hands in a sink

    Obsessive-Compulsive Disorder

    Obsessive-Compulsive Disorder (OCD) is an anxiety disorder that causes unwanted thoughts and repetitive behaviors.

  • Man in an industrial factory, holding a respirator to prevent occupational respiratory disease

    Occupational Respiratory Disease

    Work can be a dangerous place if you are exposed to hazardous toxins. Certain substances put you at risk for…

  • Hydrocodone prescription bottle

    Opioid Addiction

    An opioid addiction is a powerful urge to use opioids. These are medicines that are prescribed to relieve pain, such…

  • A photo of a troubled teen meeting with his psychologist

    Oppositional Defiant Disorder

    Oppositional defiant disorder, or ODD, is a behavior condition that affects children and teens. Those who have it are angry,…

  • 3D illustration of DNA molecule

    Organic Acid Metabolism Disorders

    Organic acid metabolism disorders are a group of rare birth defects. They affect your ability to break down food into…

  • Doctor examines knee of teenage boy seated on examination bed. Osgood-Schlatter disease causes swelling and knee pain. It can be caused by pulled or overused muscles around one or both knees.

    Osgood-Schlatter Disease

    Osgood-Schlatter disease is one of the most common causes of knee pain in young children and athletes. It can affect…

  • older woman sits on bed with her hand on her hip in pain


    Arthritis is swelling of the joints. It’s painful and can limit your movement. There are many kinds of arthritis. Osteoarthritis…

  • Osteochondritis Dissecans

    Osteochondritis dissecans is a joint problem. It occurs when an area of bone under a piece of cartilage in the…

  • Osteopenia

    Osteopenia is a condition that begins as you lose bone mass and your bones get weaker.

  • Osteoporosis

    Osteoporosis is a disease of the bones and often occurs in older women.

  • Osteosarcoma

    Osteosarcoma is a bone cancer that most often affects people between the ages of 10 and 20. It usually begins…

  • Swimmer’s ear, also known as otitis externa, is an irritation, swelling or infection in your ear. It can be caused by bacteria and fungus.

    Otitis Externa (Swimmer's Ear)

    Swimmer’s ear, also known as otitis externa, is an irritation, swelling or infection in your ear. It can be caused…

  • doctor examining the ear of a young smiling girl

    Otitis Media (with Effusion)

    Otitis media with effusion means there is fluid in the middle ear. It is common in young children and usually…

  • Ovarian Cancer

    Ovarian cancer is cancer in one or both ovaries. Ovaries are small organs located on each side of a women’s…

  • Ovarian Cyst

    An ovarian cyst is a fluid-filled sac in or on a person’s ovary. It is very common. Many times, these…

  • Two young women chatting in a coffee shop

    Overactive Bladder

    Overactive bladder is a condition that causes you to lose control of your bladder without warning.