The most common cause of shaking hands is Essential Tremor (ET) rather than Parkinson's disease (PD). With ET, the tremor usually gets worse when the muscle is in use. With PD, the tremor is worse when the muscle is at rest and decrease when you move the muscle.
Essential tremor is also the most common neurologic disorder affecting adults. It is likely caused by a disruption in the normal functioning of the cerebellum. People with essential tremor experience frequent shaking. The shaking most often occurs in the hands, arms, head, and vocal cords.
Parkinson's disease is a chronic, degenerative neurological disorder. The exact cause of Parkinson's disease is unknown, although research points to a combination of genetic and environmental factors.
Shaky hands can also be caused by seizure, overactive thyroid, cerebellar disease, Huntington’s disease, medication side effects, caffeine overdose, drinking alcohol, anxiety or low blood sugar.