Tremor is an involuntary, rhythmic muscle contraction leading to shaking movements in one or more parts of the body. It is a common movement disorder that most often affects the hands but can also occur in the arms, head, vocal cords, torso, and legs.Essential tremor is a nervous system (neurological) disorder that causes involuntary and rhythmic shaking. It can affect almost any part of your body, but the trembling occurs most often in your hands — especially when you do simple tasks, such as drinking from a glass or tying shoelaces.Tremors are usually caused by problems with areas of the brain that control movements. Neurological problems can cause tremors, but they can also be caused by metabolic problems and toxins (such as alcohol) that affect the brain and nervous system. … Shaking hands can occur at rest or during directed movements.