Obesity is a chronic disease affecting millions of people worldwide, characterized by excessive body fat that can harm health and quality of life. It goes beyond appearance, involving complex interactions between genetics, behavior, environment, and metabolism, and requires comprehensive, long-term management strategies.

Obliterative bronchiolitis is a rare but serious lung disease where the smallest airways become inflamed, damaged, and scarred. This scarring causes permanent narrowing of these airways, making it progressively harder to breathe. While the disease cannot be cured, treatments can help manage symptoms and slow its progression.

Obsessive-compulsive disorder is a mental health condition where unwanted, intrusive thoughts drive people to perform repetitive behaviors over and over again, often consuming hours each day and interfering with normal life activities.

Obstructive airways disorder affects millions of people worldwide, making it difficult to breathe and limiting daily activities. Understanding this condition and its management can help improve quality of life and reduce serious complications.

Obstructive pancreatitis is a form of chronic pancreatitis that develops when something blocks or narrows the main pancreatic duct, causing inflammation and damage to the pancreas over time.

Obstructive sleep apnoea syndrome is a common sleep disorder that causes you to stop breathing repeatedly throughout the night, leaving you exhausted during the day and putting your health at serious risk if left untreated.

Ocular hypertension means the pressure inside your eye is higher than normal, but without damage to the optic nerve. While it often causes no symptoms, this condition affects millions of people and requires careful monitoring to prevent vision loss from glaucoma.

Ocular lymphoma is a rare cancer that originates in white blood cells and can affect any part of the eye and surrounding tissues, often mimicking common eye conditions and making diagnosis challenging.

Ocular melanoma is the most common eye cancer in adults and the second most common type of melanoma after skin melanoma, yet it remains largely unknown to the public despite affecting approximately 2,000 adults each year in the United States.

Ocular myasthenia is a form of myasthenia gravis where muscle weakness affects only the eyes and eyelids, causing symptoms like drooping eyelids and double vision that can vary throughout the day.

Oedema is swelling caused by excess fluid trapped in the body’s tissues, most commonly affecting the feet, ankles, and legs, though it can occur anywhere in the body.

Peripheral oedema is swelling in the lower legs, ankles, feet, or hands caused by a buildup of fluid in the body’s tissues, ranging from minor discomfort after prolonged sitting to a sign of serious heart, kidney, or liver disease.

Oesophageal achalasia is a rare swallowing disorder where damaged nerves prevent the muscles of the food pipe from working properly, making it difficult to swallow food and drink. Though there is no cure, symptoms can usually be managed with treatment options ranging from medication to surgery.

Oesophageal adenocarcinoma is a type of cancer that begins in the glandular cells of the lower part of the food pipe, where it meets the stomach. This cancer has become more common in recent decades, especially in the United States and western Europe, and most often affects men over the age of 50.

Stage 2 oesophageal adenocarcinoma is a type of cancer that begins in the gland cells of the oesophagus and has grown into deeper layers of the oesophagus wall, sometimes spreading to nearby lymph nodes, but has not reached other parts of the body.

Stage 3 oesophageal adenocarcinoma is a serious form of cancer where the disease has grown deeper into the oesophagus and may have spread to nearby lymph nodes, but has not reached distant parts of the body. Understanding this stage helps patients and their families prepare for treatment and know what to expect.

Oesophageal atresia is a birth defect where a baby’s food tube doesn’t connect properly to the stomach, making it impossible to swallow or feed normally. Most babies need surgery shortly after birth to repair this condition.

Metastatic oesophageal cancer means that cancer which started in the food pipe has spread to distant parts of the body. This advanced stage affects around half of all patients at the time of diagnosis and presents complex challenges that require comprehensive care and support.

Oesophageal carcinoma is a cancer that starts in the oesophagus, the muscular tube that carries food from your throat to your stomach. Most people don’t notice symptoms until the disease has progressed, making early detection challenging but crucial for better outcomes.

Oesophageal disorders are a collection of conditions that affect the tube carrying food from your mouth to your stomach, with symptoms ranging from heartburn to difficulty swallowing that can significantly impact your daily life.

When a piece of food gets stuck in the tube that carries food from your mouth to your stomach, it creates a frightening situation that sends thousands of people to the emergency room each year. While many cases resolve on their own, some require urgent medical attention to prevent serious complications.

Oesophageal squamous cell carcinoma is a type of cancer that affects the esophagus, the muscular tube connecting your throat to your stomach. This form of cancer usually develops in the upper or middle part of the esophagus and often remains undetected until advanced stages, making early recognition and proper treatment critical.

Oesophageal squamous cell carcinoma metastatic represents the most advanced form of esophageal cancer, where cancer cells have spread beyond the esophagus to distant parts of the body such as the liver, lungs, or bones, fundamentally changing both treatment approaches and patient outlook.

Stage II oesophageal squamous cell carcinoma represents a stage where the cancer has grown deeper into the layers of the oesophagus and may have reached nearby lymph nodes, but has not spread to distant organs.

Stage III oesophageal squamous cell carcinoma is an advanced form of cancer that affects the food pipe, where the disease has spread beyond the oesophagus lining into deeper tissues or nearby lymph nodes, but has not yet reached distant parts of the body.

Oesophagectomy is major surgery to remove all or part of the oesophagus, the tube that carries food from your throat to your stomach. This procedure is most often performed to treat oesophageal cancer and requires careful preparation, extensive surgery, and a long recovery period.

Oesophagogastroscopy, also called upper endoscopy or EGD, is a medical procedure that allows doctors to examine the inside of your upper digestive system using a flexible tube with a camera. This procedure helps diagnose and sometimes treat various digestive problems affecting your esophagus, stomach, and the beginning of your small intestine.

Oestrogen receptor gene overexpression occurs when cells produce too much of the protein that responds to oestrogen hormones, affecting how genes are turned on and off in the body, with important implications for breast cancer development and treatment.

Onychomycosis is a fungal infection of the nail that can make your nails thick, discolored, and brittle. While it’s not usually painful, this common condition affects millions of people and can significantly impact daily life and self-confidence.

Open-angle glaucoma is a silent eye condition that can steal your vision without warning. Understanding this disease and getting early treatment can help protect your sight for years to come.

Ophthalmoplegia is a condition that affects the muscles controlling your eye movements, causing weakness or paralysis that can lead to drooping eyelids, double vision, and difficulty moving your eyes. Understanding this condition and its various forms is essential for proper diagnosis and treatment.

Optic atrophy is a serious condition affecting the optic nerve, which connects your eyes to your brain. It can lead to permanent vision loss and even blindness, making early detection and treatment of underlying causes critically important.

Optic glioma is a slow-growing brain tumor that develops along the optic nerve, the pathway that carries visual signals from the eye to the brain. While this is a serious condition, it has a high cure rate and primarily affects young children, with most cases diagnosed before the age of 5.

Optic ischaemic neuropathy is a serious condition that causes sudden vision loss when the optic nerve doesn’t receive enough blood flow. It most commonly affects people over 50 and requires urgent medical attention to prevent permanent damage.

Oral herpes is a very common viral infection that affects the mouth and lips, causing small blisters known as cold sores. About half of adults in the United States have this infection, often contracted during childhood through everyday contact like kissing. While there is no cure, the condition can be effectively managed with treatment.

Oral lichen planus is a long-lasting inflammatory condition that affects the tissue lining inside your mouth, appearing as white patches, red areas, or open sores, and while it cannot be cured, treatments can help manage symptoms and reduce discomfort.

Oral neoplasm, also known as mouth cancer or oral cavity cancer, affects the lips, tongue, gums, and other parts of the mouth. Early detection can make a significant difference in treatment success, but many cases are discovered only in later stages.

Organ donation offers a second chance at life to people with life-threatening diseases or injuries to their vital organs. One organ donor can save up to eight lives and enhance the lives of 75 others through organ, eye and tissue donation.

Ornithine transcarbamoylase deficiency is a rare inherited disorder that prevents the body from safely removing ammonia from the blood, potentially causing severe brain damage if ammonia levels become too high.

Oropharyngeal cancer forms in the middle section of your throat and can affect your ability to eat, drink, and speak. While the disease is relatively rare, affecting about 53,000 people in the U.S. each year, its incidence is rising—especially cases linked to human papillomavirus (HPV) infection, which now accounts for 60% to 70% of all oropharyngeal cancers.

Recurrent oropharyngeal cancer means the cancer has returned after initial treatment. Despite advances in treatment and the generally favorable prognosis of oropharyngeal cancer—especially when linked to human papillomavirus (HPV)—some patients will experience recurrence, which requires specialized care and a personalized approach to treatment.

Oropharyngeal squamous cell carcinoma is a type of cancer that develops in the middle part of the throat, affecting areas like the tonsils, base of the tongue, and soft palate. While cases are rising, especially in younger people, treatment options are improving and cure rates are increasing, particularly for cancers linked to human papillomavirus (HPV).

Orthostatic hypotension is a sudden drop in blood pressure that happens when you stand up from sitting or lying down. This condition can make you feel dizzy or lightheaded, and sometimes even cause you to faint. While it can affect anyone, it becomes more common with age and can significantly impact daily life.

Osteoarthritis is the most common form of arthritis worldwide, affecting millions of people. While there is no cure, understanding this condition and knowing how to manage it can help you maintain an active, fulfilling life and slow its progression.

Osteochondrodysplasia represents a group of rare hereditary disorders that disrupt the normal development of bone and cartilage, leading to skeletal abnormalities and short stature in affected individuals.

Osteogenesis imperfecta is a genetic disorder that causes bones to break easily, often from little or no force. While some people experience only a few fractures in their lifetime, others may face hundreds of breaks, along with additional health challenges affecting the teeth, hearing, spine, and breathing.

Osteomyelitis is a serious bone infection that can affect anyone, but early diagnosis and treatment are crucial to prevent permanent damage and restore normal function.

Acute osteomyelitis is a serious bone infection that develops rapidly when bacteria or fungi spread to your bones, usually through your bloodstream. If not treated quickly, it can cause permanent bone damage and serious complications.

Osteonecrosis of the jaw is a rare but serious condition where bone tissue in the jaw dies and becomes exposed through the gums. While uncommon, it can occur in people taking certain medications for osteoporosis or cancer, particularly after dental procedures.

Osteopenia is a condition where your bones lose density and become weaker than normal, though not weak enough to be classified as osteoporosis. About 40 million Americans have osteopenia, and it typically develops after age 50, though the exact timing depends on how strong your bones were when you were younger.

Osteoporosis weakens your bones, making them fragile and more likely to break from even a minor fall or bump. Often called a “silent disease,” it develops slowly over many years without obvious symptoms, and many people only discover they have it after breaking a bone.

Postmenopausal osteoporosis is a condition where bones become weak and brittle after menopause, affecting millions of women worldwide. Understanding this condition and taking proactive steps can help protect your bone health and reduce the risk of fractures.

Osteosarcoma is a type of bone cancer that most often affects teenagers and young adults, though it can occur at any age. It typically develops in the long bones of the arms and legs, especially near the knee, and can cause pain, swelling, and limited movement.

Metastatic osteosarcoma is when bone cancer spreads from its original location to other parts of the body, most commonly the lungs. This advanced form of bone cancer presents significant treatment challenges and has a less favorable outlook than cancer that remains in one place.

Recurrent osteosarcoma is cancer that has returned after initial treatment or has not responded to therapy. It occurs in 30-50% of patients who initially had cancer confined to one area, and in 80% of patients who had cancer that had already spread at diagnosis.

Osteotomy is a surgical procedure that cuts and reshapes bones to correct alignment problems, relieve pain, and restore movement to damaged joints throughout the body.

Otitis media is an infection or inflammation of the middle ear, the space behind your eardrum. It’s the most common childhood illness after colds, affecting up to 80% of children before they reach school age. While it can be painful and worrying for parents, most ear infections clear up on their own, though some cases may need antibiotics or other treatments.

Ovarian cancer is a disease where abnormal cells in the ovaries grow out of control. It often develops without obvious symptoms in the early stages, making early detection challenging. Understanding the warning signs, risk factors, and treatment options can help you take charge of your health.

Metastatic ovarian cancer

When ovarian cancer returns after treatment, it brings new challenges—but also new possibilities for care. Understanding what recurrence means and the options available can help you navigate this next phase of your journey.