Parkinson's disease (PD), or simply Parkinson's is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly and, as the disease worsens, non-motor symptoms become more common. The most obvious early symptoms are tremor, rigidity, slowness of movement, and difficulty with walking, but cognitive and behavioral problems may also occur. Parkinson's disease dementia becomes common in the advanced stages of the disease. Depression and anxiety are also common, occurring in more than a third of people with PD. Other symptoms include sensory, sleep, and emotional problems. The main motor symptoms are collectively called "parkinsonism", or a "parkinsonian syndrome".While the cause of PD is unknown, it is believed to involve both inherited and environmental factors. Those with a family member affected are more likely to get the disease themselves. There is also an increased risk in people exposed to certain pesticides and among those who have had prior head injuries, while there is a reduced risk in tobacco smokers and coffee or tea drinkers. The motor symptoms of the disease result from the death of cells in the substantia nigra, a region of the midbrain, leading to a dopamine deficit. The cause of this cell death is poorly understood, but involves the build-up of proteins into Lewy bodies in the neurons.Diagnosis of typical cases is mainly based on symptoms, with tests such as neuroimaging used to rule out other diseases. Parkinson's disease typically occurs in people over the age of 60, of whom about one percent are affected. Males are more often affected than females at a ratio of around 3:2. When it is seen in people before the age of 50, it is called early-onset PD. In 2015, PD affected 6.2 million people and resulted in about 117,400 deaths globally. The average life expectancy following diagnosis is between 7 and 15 years.There is no cure for PD; treatment aims to improve the symptoms. Initial treatment is typically with the medication levodopa (L-DOPA), followed by dopamine agonists when levodopa becomes less effective. As the disease progresses, these medications become less effective, while at the same time producing a side effect marked by involuntary muscle movements. Diet and some forms of rehabilitation have shown some effectiveness at improving symptoms. Surgery to place microelectrodes for deep brain stimulation has been used to reduce motor symptoms in severe cases where drugs are ineffective. Evidence for treatments for the non-movement-related symptoms of PD, such as sleep disturbances and emotional problems, is less strong.The disease is named after the English doctor James Parkinson, who published the first detailed description in An Essay on the Shaking Palsy, in 1817. Public awareness campaigns include World Parkinson's Day (on the birthday of James Parkinson, 11 April) and the use of a red tulip as the symbol of the disease. People with Parkinson's who have increased the public's awareness of the condition include the boxer Muhammad Ali, actor Michael J. Fox, Olympic cyclist Davis Phinney, and actor Alan Alda.