Menstruation is the monthly shedding of the uterine lining, resulting in bleeding from the vagina that typically lasts 3 to 7 days. It happens when the body prepares for pregnancy each cycle and no fertilized egg implants. A normal menstrual cycle repeats every 24 to 38 days, with 28 days being the most commonly cited average.
Why the Body Sheds Its Lining
Each month, the inner lining of the uterus (called the endometrium) thickens in response to rising levels of estrogen and progesterone. These hormones signal the body to build a nutrient-rich environment where a fertilized egg could attach and grow. If no egg is fertilized, hormone levels drop sharply. Without that hormonal support, the thickened lining breaks down and exits the body through the vagina as a mix of blood, tissue, and mucus. That flow is your period.
The Four Phases of the Cycle
A full menstrual cycle has four distinct phases, and menstruation is just the first one.
Menstruation (Days 1 Through 3–7)
This is the bleeding phase. Day 1 of your period is also day 1 of your cycle. Most people bleed for 3 to 7 days, losing less than 60 milliliters of blood in a typical period. That’s roughly 4 tablespoons. Anything over 80 milliliters is considered heavy bleeding.
Follicular Phase (Days 1 Through 13–14)
This phase actually overlaps with menstruation and continues after bleeding stops. The pituitary gland, a small structure at the base of the brain, releases a hormone that stimulates the ovaries to develop small fluid-filled sacs called follicles. Each follicle contains an egg. Usually one follicle matures faster than the others, and rising estrogen levels start rebuilding the uterine lining again.
Ovulation (Around Day 14)
A surge of luteinizing hormone from the pituitary gland triggers the release of a mature egg from the ovary. This ovulatory phase lasts roughly 16 to 32 hours, and the egg is released about 10 to 12 hours after that hormone surge peaks. This is the window when pregnancy is possible. Home ovulation kits work by detecting that hormone surge in urine.
Luteal Phase (Days 15 Through 28)
After the egg is released, it travels through the fallopian tube toward the uterus. The empty follicle left behind on the ovary starts producing progesterone, which keeps the uterine lining thick and ready. If the egg isn’t fertilized within about 24 hours, it dissolves. Progesterone levels eventually fall, the lining destabilizes, and a new period begins.
Common Physical and Emotional Symptoms
Many people experience symptoms in the days leading up to their period, commonly called PMS (premenstrual syndrome). Physical symptoms include abdominal bloating, breast tenderness, headaches, fatigue, joint or muscle pain, acne flare-ups, and digestive changes like constipation or diarrhea. Some people also notice temporary weight gain from fluid retention.
Emotional and behavioral shifts are equally common. These can range from irritability and mood swings to anxiety, difficulty concentrating, trouble sleeping, food cravings, and feeling socially withdrawn. Not everyone experiences PMS, and symptoms can vary widely from one cycle to the next.
Cramping during the period itself is caused by the uterus contracting to help shed its lining. Mild to moderate cramps are normal, though for some people the pain can be severe enough to interfere with daily activities.
When Periods Typically Start and Stop
Most people get their first period (called menarche) between the ages of 10 and 15. If menstruation hasn’t started by age 15 or 16, or within three years of breast development beginning, that’s worth discussing with a healthcare provider.
Periods continue until menopause, which most women experience between the ages of 45 and 55. In the years leading up to menopause, cycles often become less predictable, with longer gaps between periods or changes in flow.
Managing Your Period
The most widely used period products are pads (sanitary napkins), regular tampons, panty liners, and super-absorbent tampons. A smaller but growing number of people use menstrual cups or period underwear. Menstrual cups are flexible silicone or rubber devices shaped like a small funnel that sit inside the vagina and collect flow rather than absorbing it. Period underwear has built-in absorbent layers designed to contain menstrual fluid without additional products.
There’s no single “right” product. Many people use different products at different points in their cycle, switching from a tampon or cup during the day to a pad at night, for instance. About 60% of tampon users report wearing them overnight, while 40% switch to another product for sleeping. Tampons should generally be changed every 4 to 8 hours to reduce the risk of infection.
Signs of an Irregular Period
Your cycle doesn’t need to land on exactly 28 days to be normal. Anywhere from 24 to 38 days is considered a healthy range. But certain patterns signal something worth investigating:
- Very short or very long cycles: periods arriving fewer than 21 days or more than 35 days apart.
- Highly variable cycle length: if the gap between cycles varies by more than 9 days from month to month (for example, 28 days one cycle, then 37 the next).
- Missing periods: going 90 days or more without a period when you’re not pregnant, breastfeeding, or approaching menopause.
- Very heavy bleeding: soaking through a pad or tampon in an hour, or bleeding that lasts longer than 7 days.
- Bleeding between periods: spotting or bleeding that occurs outside your regular period, or after sex.
- Severe pain: cramping accompanied by nausea or vomiting, or pain that prevents normal activity.
Tracking your cycles can help you spot these patterns early. Recording the start and end date of each period, the heaviness of your flow, and any unusual symptoms gives you concrete information to share if you do need medical advice.