Systemic mastocytosis
Overview Systemic mastocytosis (mas-to-sy-TOE-sis) is a rare disorder that results in too many mast cells building up in your body. A mast cell is a type of white blood cell.…
Systemic capillary leak syndrome
Overview Systemic capillary leak syndrome is a rare disorder characterized by repeated flares of massive leakage of plasma from blood vessels into neighboring body cavities and muscles. This results in…
Syringomyelia
Overview Syringomyelia cyst (syrinx) in the spinal cord Syringomyelia (sih-ring-go-my-E-lee-uh) is the development of a fluid-filled cyst (syrinx) within your spinal cord. Over time, the cyst can enlarge, damaging your…
Syphilis
Overview Syphilis is a bacterial infection usually spread by sexual contact. The disease starts as a painless sore — typically on the genitals, rectum or mouth. Syphilis spreads from person…
Soft tissue sarcoma
Synovial sarcoma Synovial sarcoma is a rare type of cancer that tends to arise near large joints, particularly the knee, in young adults. Despite its name, it typically doesn’t affect…
Swollen lymph nodes
Overview Lymph node locations Swollen lymph nodes Swollen lymph nodes usually occur as a result of infection from bacteria or viruses. Rarely, swollen lymph nodes are caused by cancer. Your…
Swollen knee
Overview A swollen knee occurs when excess fluid accumulates in or around your knee joint. Your doctor might refer to this condition as an effusion (ih-FYU-zhen) in your knee joint.…
Swimmer’s itch
Overview Swimmer’s itch Swimmer’s itch is an itchy rash that can occur after you go swimming or wading outdoors. Also known as cercarial dermatitis, swimmer’s itch is most common in…
Swimmer’s ear
Overview Outer ear infection Swimmer’s ear is an infection in the outer ear canal, which runs from your eardrum to the outside of your head. It’s often brought on by…
Sweet’s syndrome
Overview Sweet’s syndrome Sweet’s syndrome, also called acute febrile neutrophilic dermatosis, is an uncommon skin condition. It causes fever and a painful skin rash that appears mostly on the arms,…
Sweating and body odor
Overview Sweating and body odor are common when you exercise or you’re too warm. They’re also common when you’re feeling nervous, anxious or stressed. Unusual changes in sweating — either…
Suspicious breast lumps
Overview A breast lump is a growth of tissue that develops within your breast. Finding a lump in your breast can be frightening and provoke anxiety. Most breast lumps aren’t…
Supraventricular tachycardia
Overview Supraventricular tachycardia (SVT) is as an abnormally fast or erratic heartbeat that affects the heart’s upper chambers. An abnormal heartbeat is called an arrhythmia. SVT is also called paroxysmal…
Sunburn
Overview Sunburn is red, painful skin that feels hot to the touch. It usually appears within a few hours after too much exposure to ultraviolet (UV) light from sunshine or…
Sun allergy
Overview Sun allergy is a term often used to describe a number of conditions in which an itchy red rash occurs on skin that has been exposed to sunlight. The…