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.
It's usually not a dangerous condition, but essential tremor typically worsens over time and can be severe in some people. Other conditions don't cause essential tremor, although it's sometimes confused with Parkinson's disease.
Essential tremor can occur at any age but is most common in people age 40 and older.
Essential tremor care at Mayo Clinic