Why do my hands shake? Most tremor is normal or essential, not Parkinson's

The shake you notice when you hold a full cup, thread a needle or stretch your hands out in front of you is, for most people, an action tremor — and the most common versions are not signs of disease. A tremor is simply an involuntary, rhythmic, oscillating movement of a body part [s1], and the two everyday causes are the fine physiological tremor that everyone has, amplified by things like caffeine and stress, and essential tremor, the commonest tremor disorder [s2]. The pattern people most fear, Parkinson's disease, characteristically does the opposite: it produces a tremor that is worst at rest and settles when the hand is used [s3].

That rest-versus-action distinction is the single most useful thing to understand, because it separates the reassuring from the worth-checking without any test at all.

Everyone has a tremor

Movement-disorder specialists classify tremors partly by when they appear — at rest, or during a voluntary movement such as holding a posture or reaching [s1]. Enhanced physiological tremor is a fine, small-amplitude action tremor in both hands that many people experience transiently, and it can be triggered by stress or strong emotion, physical tiredness, and certain postures [s3]. Its common amplifiers are worth naming because they are within a person's control: excessive caffeine can cause a temporary tremor or make an existing one worse [s3], and our guide to how much caffeine is too much covers where that line sits. Several drugs — including some asthma medicines, corticosteroids and chemotherapy agents — can do the same, as can an overactive thyroid and low blood sugar; this kind of tremor is potentially reversible once the cause is corrected [s3]. The same adrenaline-driven physiology underlies the jitter some people feel from stimulants, a theme our report on coffee and heart palpitations picks up.

Essential tremor: common, and more so with age

When a hand tremor is persistent and appears on action — holding a cup, writing, using utensils — rather than at rest, the likeliest label is essential tremor, one of the most common movement disorders [s3]. It is not rare: a meta-analysis of 28 population studies across 19 countries put the pooled prevalence across all ages at 0.9% [s2]. The striking feature is how sharply it climbs with age. In the same meta-analysis prevalence reached 4.6% in those aged 65 and over, and one study of people aged 95 and older found it in 21.7% [s2]. Essential tremor is often familial and tends to worsen gradually over years; it is a nuisance far more often than it is disabling, though it can become socially and practically limiting.

The tremor that points elsewhere

The reason the rest-versus-action split matters is that a rest tremor — present when the limb is completely supported and relaxed, and easing when the hand moves — is the pattern often seen in Parkinson's disease [s3]. A new tremor of that kind, especially with slowness of movement, stiffness, a change in handwriting or a shuffling gait, is worth a clinician's assessment rather than watchful waiting; our coverage of newer Parkinson's drug trials gives a sense of how that condition is managed. Other features that lift a tremor out of the benign category include sudden onset, a tremor confined to one side, or one that appears soon after starting a new medication [s3].

What it means for a reader

A fine shake that shows up when you are tired, anxious, cold or over-caffeinated, and eases when you relax, is the ordinary physiological tremor almost everyone has [s3]. A persistent action tremor that runs in the family and creeps up with age is most often essential tremor, common and rarely sinister [s2]. A tremor that is present at rest, one-sided, sudden, or accompanied by stiffness and slowness is the combination that deserves a proper look [s3]. This article is informational and is not medical advice; it does not diagnose any individual's tremor or recommend starting, stopping or changing any medication.

Sources

• Consensus Statement on the classification of tremors, from the task force on tremor of the International Parkinson and Movement Disorder Society — Movement Disorders, 2017-11-30
• How common is the most common adult movement disorder? Update on the worldwide prevalence of essential tremor — Movement Disorders, 2010-02-19
• Tremor — National Institute of Neurological Disorders and Stroke