(HealthDay News) -- Endometriosis occurs when uterine tissue grows outside of a woman's uterus.

The National Women's Health Information Center says the following factors may increase a woman's risk of developing endometriosis:

• Not having any children.
• Having menstrual periods of longer than seven days.
• Having menstrual cycles of 27 days or shorter.
• Having someone in the family who has had endometriosis.
• Having a health condition that affects the ability to menstruate normally.
• Having had a pelvic infection that caused cell damage.