Hot flashes, also known as vasomotor symptoms, and can begin many years before the onset of menopause (menopause is defined retrospectively at 12 months after the cessation of menstruation). As estrogen levels begin to drop off in your mid-30’s, you may begin to notice vague symptoms that continue to increase until you get to the stage called perimenopause. This is the most symptomatic stage of menopause, it usually starts in your mid-40’s and typically lasts 6 years.