Amenorrhea is the medical term for the absence of menstrual periods, either on a permanent or temporary basis.

Amenorrhea can be classified as primary or secondary.

In primary amenorrhea, menstrual periods have never begun (by age 16), whereas secondary amenorrhea is defined as the absence of menstrual periods for three consecutive cycles or a time period of more than six months in a woman who was previously menstruating.

The menstrual cycle can be influenced by many internal factors such as transient changes in hormonal levels, stress, and illness, as well as external or environmental factors.

Missing one menstrual period is rarely a sign of a serious problem or an underlying medical condition, but amenorrhea of longer duration may signal the presence of a disease or chronic condition.

What causes amenorrhea? 
The normal menstrual cycle occurs because of changing levels of hormones made and secreted by the ovaries.

The ovaries respond to hormonal signals from the pituitary gland located at the base of the brain, which is, in turn, controlled by hormones produced in the hypothalamus of the brain.

Disorders that affect any component of this regulatory cycle can lead to amenorrhea.

However, a common cause of amenorrhea in young females sometimes overlooked or misunderstood by the individual and others, is an undiagnosed pregnancy.

Amenorrhea in pregnancy is a normal physiological function.

Occasionally, the same underlying problem can cause or contribute to either primary or secondary amenorrhea.

For example, hypothalamic problems, anorexia, or extreme exercise can play a major role in causing amenorrhea depending on the age of the person and if she has experienced menarche.