If you see someone with shaking hands or other bodily tremors, you might assume he or she has Parkinson's disease, which is a high-profile condition with tremor as a common symptom. However, many conditions cause tremor. One of the most common causes of tremor—essential tremor—is seven times more common than Parkinson's disease, affecting about 7 million Americans. Several types of tremor exist, with a wide variety of causes. Diseases That Can Cause Tremor Tremor is a rhythmic muscle contraction that you can't control. Most often, it strikes the hands. But it can also affect other parts of the body, such as the arms, head, torso, legs and even the vocal cords, resulting in a shaky voice. Some tremors occur when a person is at rest; others, when someone tries to make movements. Tremor can come and go, or be constant, depending on the type; it can occur at any age (though middle-aged and older adults are more likely to have it); and affects both genders equally. The underlying reason the body shakes is due to a problem in the brain's ability to control movement. But why does the brain fail? Sometimes this is due to medical conditions, which include neurological disorders and other illnesses. Among them: Multiple sclerosis Stroke Parkinson's disease Ataxia (an inherited degenerative disease of the nervous system) Fragile X syndrome (a relatively rare genetic syndrome that can cause developmental delays) Overactive thyroid (hyperthyroidism) Liver or kidney failure Anxiety or panic disorder Hypoglycemia (low blood sugar) Another cause for tremor is a condition called essential tremor. This common neurological disorder is so named because it has tremor as its primary symptom. The disorder—often confused in its early stages with Parkinson's—is caused by a genetic mutation in about half the people who suffer from it. For these people, the disorder is called familial tremor. It's unknown why the other half of people with essential tremor develop it. Researchers believe the cause is a defect in the thalamus or cerebellum in the brain, but so far, imaging studies haven't borne this out. Other Causes of Tremor Tremor can be triggered by other factors besides illness. For example, caffeine has been shown to cause shaking hands in 2% of coffee-drinkers who didn't otherwise have tremor. Caffeine also can make tremor worse if someone already has a condition such as Parkinson's disease. Similarly, these other factors can also potentially trigger or worsen tremor: Stress Emotion Sleep deprivation Physical exhaustion Taking certain medications (such as some antidepressants, corticosteroids, and drugs used to treat neurological disorders) Alcohol withdrawal Tremor is a complicated syndrome with many causes. In some cases, it is inherited. If you have a family history of tremor, or experience uncontrollable shaking in any part of your body, bring this to your health provider's attention. Treatment may be available, depending on the cause of your tremor.