A muscle twitch is a small, involuntary contraction and relaxation of a muscle group or single motor nerve. These twitches are very common and usually go unnoticed. Sometimes, however, they may become excessive or uncomfortable and may need attention. The causes of a muscle twitch can be varied, ranging from an overdose of caffeine to nerve damage. In many cases, the causes are benign and can resolve on their own or be easily treated, while other cases may require medical intervention.

Exercise and stress are two of the most common causes of a muscle twitch. Spasms may occur in any muscle of the body during a workout, but are mostly felt in the hands and arms as well as the legs and feet. Twitching will usually occur because certain chemicals are released into the body after a stressful workout, which may change the excitability of muscle tissue. Anxiety and stress may also trigger muscle twitches, which can affect both the body and face. Stress-related causes of a muscle twitch are often thought to be the result of an internal fight or flight response, but may also come about due to the source of stress, such as dehydration or extreme pain.

Sometimes the causes of a muscle twitch are benign and are not linked to a physical illness. Overdoses of certain chemicals may cause involuntary spasms in the muscles, and this is especially true with beverages and foods that contain caffeine. In addition, certain medications such as estrogen therapies, diuretics and corticosteroids may have muscle twitching as a side effect.

Although most causes of a muscle twitch are harmless, others may be more severe. Should involuntary spasms be caused by an underlying condition, they will often be one of many symptoms. For instance, Lou Gehrig's disease may cause spasms along with muscle weakness and cramping as well as slurred speech and shortness of breath. While anemia, in addition to muscle twitches, may cause headaches, dizziness or fatigue.

Though some underlying causes of a muscle twitch may be severe, many others are due to damaged or pinched nerves. There are more than 100 different types of nerve damage, and their causes are various. Some damage may be caused by autoimmune diseases or cancer; others may come about due to motor neuron diseases or trauma. Although these conditions will present a host of additional symptoms, motor nerve damage will also sometimes cause paralysis as well as weakness and muscle atrophy.