Tremor is a rhythmic motion of a body part, to include the head, neck, body, arms, hands, legs and feet. Tremor is sometimes confused with fast-jerking movements that can happen when muscles become overly tired. The body part affected depends on the cause or source of the tremor. Tremor can onset early, middle or late age and affects women equally as often as men.

Cause

Tremor can be caused by medications, toxins, medical conditions, brain disorders and injury.  Tremor runs in some families. When tremor is noticed, a Neurologist can help determine the cause of the tremor and suggest treatment if needed. 

The most common cause of tremor is Essential tremor. It is sometimes referred to as familial tremor because more than one family member may have this in up to 40% of cases. This tremor is usually in the hands but can also occur in the head, voice and rarely legs. Tremor is usually worse when using you hands and improves with hands and arms at rest by your side. Because of this, find coordination of the hands is affected making activities such as writing, eating and dressing difficult. This is different than the rest tremor found in Parkinson's disease (link). In this condition tremor actually improves with action. Treatment includes medications and in some cases Deep Brain stimulation (link). An occupational therapist (link) can also help you with daily activities that are worsened by tremor. 
 
Other common causes of tremor include:

Brain Disorders:  Parkinson’s disease or atypical parkinsonism, Dystonia and Wilson’s disease.

Medical Conditions:  thyroid disorders, liver disorders, anxiety, low magnesium, calcium or blood sugar, and neuropathy.

Injury: stroke or other damage to the brain, spinal cord, neck, arms or legs can cause tremor.

Medications:  some medications are known to cause or worsen tremor to include medications used for mood disorders, lung disorders, heart disorders and any stimulant. 

Toxins that can cause tremor include mercury, arsenic, manganese, cyanide, lead.

Other causes include alcohol use, caffeine, and nicotine. Tremor can also occur from excessive stress.