Fibromyalgia is considered to be a syndrome-a set of symptoms that occur together but do not have a known cause. There are theories as to what may cause it, but there is not enough evidence to support any single theory. People-especially women-who have a family member with fibromyalgia are more likely to develop it themselves. It has been recognized as a medical disorder only since the 1980s.

Some theories suggest that fibromyalgia may be linked to:

• Oversensitive nerve cells in the spinal cord and brain. Oversensitivity may be due to changes in chemicals in the brain or spinal cord that regulate pain. As a result, the person senses pain more easily, and widespread muscle pain occurs.
• An imbalance in the brain chemicals that control mood, which results in a lowered tolerance for pain and may also cause an unrestful sleep cycle and fatigue. Once this happens, a person becomes less physically active, and the muscles and tissues become more sensitive and painful and more easily irritated.
• An imbalance of hormones such as cortisol and growth hormone. Their release is controlled by the pituitary gland and the hypothalamus. Imbalances of these hormones can result in fatigue, mood changes, concentration and memory difficulties, a lowered tolerance for pain, and other symptoms.
• A disturbance in the deep phase of sleep. Some chemicals, such as growth hormone, are secreted by the body during this phase of sleep. If sleep is disrupted, the body produces less of the hormone. Disturbed sleep may be both a cause and an effect of the pain of fibromyalgia.

Many people connect the beginning of their fibromyalgia symptoms to a certain event. These events can include an illness such as the flu, an injury or surgery, or emotional trauma and stress.¹ An event of this type combined with other factors, such as increased sensitivity to pain and an ongoing sleep disturbance, may lead to fibromyalgia syndrome in some people.