Many factors can cause infrequent periods, and these conditions may require treatment. At the same time, infrequent periods might be normal for you. While the average woman has a period every 21 to 35 days, others may only menstruate every six weeks. Typically, this is no problem, as long as periods occur on a regular basis. Infrequent periods are common in girls who're just starting to menstruate, because their bodies are adjusting to new hormonal conditions. This happens in reverse as women near menopause, when periods gradually become further apart. During the reproductive years, conditions which can interfere with your period include extreme exercise, stress, very low body fat, and less commonly, too much body fat. Fat affects the menstrual cycle because fat cells can raise or lower active estrogen levels. Other possible causes of infrequent periods are certain tranquilizers and anti-depressants, narcotics, thyroid problems, and ovarian cysts. In some cases, a relatively long cycle between periods is thought to be beneficial, perhaps reducing the risk of breast cancer. But an abnormal span could indicate an underlying problem. When infrequent periods are due to low levels of estrogen, you can lose bone mass, and your risk of heart disease may increase. If you're experiencing infrequent periods, especially if this is a change for you, consult a health care provider for advice.