Tremor is a normal phenomenon which is experienced by everyone. Normal tremor is referred to as "physiological tremor" and it is the slight tremor that any person will see when they, for instance, put out their hands. This tremor can be exaggerated in certain situations such as those associated with anxiety and fatigue. This is usually referred to as "exaggerated or enhanced physiological tremor".

In general, many members of the National Tremor Foundation (NTF) have pathological tremors. That is, their tremor or tremors are inappropriate in size and may interfere with normal functioning or present as a "cosmetic nuisance".

Tremor can be a common symptom of neurological disease and may be due to trauma, tumor, stroke or degenerative disease. The most common tremor condition is idiopathic or essential (cause unknown) or hereditary tremor. In fact, essential tremor is one the most common of all neurological conditions. It is estimated that four to five million people in the United States alone have such tremor. In most cases the disease runs in families. The condition is transmitted as an autosomal dominant inheritance, which means that the offspring of an affected individual will have a fifty percent chance of also having the illness.

Essential tremor is a neurological disorder in which patients exhibit a rhythmic trembling of the hands, head, legs, trunk and/or voice, which is more visible during movement or with arms outstretched, than at rest. It is recognisable when seen in postural (voluntarily maintaining a position against gravity) and kinetic (performing any kind of movement) positions. Thus, essential tremor is considered an "action" tremor. It is not believed to be associated with any disease or condition.

It can affect persons of any age, gender (both genders are equally affected) and race, it can start in adolescence or adulthood and in the majority of cases, it is inherited. The mean age at onset is 45 years. While more commonly seen in older individuals, ET can begin as early as birth. The age of onset, body part(s) affected and the severity of the tremors, typically differ from patient to patient, even within the same family. This difference from patient to patient holds true for benefits received from drug therapy as well. When tremor begins in the very elderly it has sometimes been called senile tremor The condition is slowly progressive and tremors will worsen overtime. Some individuals may have to change occupations (i.e. dentists and draftsman) or have to take early retirement.

Tremor may involve different body parts. Most often the hands are affected. Usually the dominant hand is first affected and eventually both hands may be involved. Handwriting becomes less legible and drinking liquids is difficult to manage. The individual may have to use both hands or use a straw to drink. Eating soup may become impossible. It may no longer be possible to sign a cheque in a bank or serve coffee at a luncheon. Dysfunction with fine manipulation and embarrassment are also problems. Tremor of the head may also occur. The shakiness may be a 'yes-yes" or a "no-no" movement. Embarrassment and social withdrawal may result from head tremor. Shakiness of the voice may occur which gives a quavering intonation to speaking. Tremor of the trunk and legs is seen in some patients.

Tremor is the sole symptom of this disorder and other neurological problems rarely occur. Stress and social interaction usually worsen the tremor. Small amounts of alcohol may be helpful. Unfortunately physicians who may misdiagnose it as anxiety or Parkinson's disease do not often recognise the tremor. There is also the misconception that nothing medically can be done to relieve the tremor.

Little is known about what causes this tremor, hence the eponym essential or idiopathic, which means that the cause is unknown, as with essential hypertension. Essential tremor is certainly a disorder of the central nervous system. However, it is not known what area of the brain is involved. It is also unclear why the disease occurs and how it affects the brain. A better understanding of these mechanisms would lead to better treatment and/or preventive therapy.