Menstrual Cycle: How Menstruation Works & What to Expect

What Is Menstruation and How Does It Work?

Menstruation is a monthly bleeding from the uterus that occurs when the uterine lining sheds because pregnancy has not occurred. The menstrual cycle, counted from the first day of one period to the first day of the next, typically lasts 21-35 days, with an average of 28 days. Most people bleed for 3-7 days and lose about 30-80 mL of blood per cycle.

The menstrual cycle is a complex biological process controlled by hormones that prepares the body for potential pregnancy each month. Understanding how this process works can help you better interpret your body's signals and recognize when something may need medical attention. The cycle involves the intricate interplay of hormones produced by the brain and ovaries, which coordinate the development and release of an egg and the preparation of the uterine lining.

The term "menstrual cycle" refers to the entire monthly process, while "menstruation" or "period" specifically refers to the bleeding phase. The cycle is measured from the first day of bleeding in one cycle to the first day of bleeding in the next. While 28 days is often cited as the "standard" cycle length, significant variation is completely normal. Studies show that only about 13% of cycles are exactly 28 days, with most falling somewhere between 21 and 35 days.

The amount of bleeding also varies significantly from person to person and can even vary between cycles in the same individual. On average, most people lose between 30-80 mL (approximately 2-5 tablespoons) of blood during their entire period. This may seem like a small amount, but it can feel like much more because menstrual fluid also contains tissue from the uterine lining, mucus, and other secretions.

Menstruation begins at puberty (menarche), typically between ages 10-16, and continues until menopause, which usually occurs between ages 45-55. Over a lifetime, the average person will have approximately 450 menstrual cycles. The characteristics of your cycle may change over time, with cycles often being irregular in the first few years after menarche and in the years leading up to menopause.

The Four Phases of the Menstrual Cycle

The menstrual cycle can be divided into four distinct phases, each characterized by specific hormonal changes and physical processes. Understanding these phases provides insight into the cyclical changes your body experiences each month.

Menstrual Phase (Days 1-5): The cycle begins with menstruation, when the thickened uterine lining (endometrium) is shed through the vagina. This occurs because the egg from the previous cycle was not fertilized, causing hormone levels to drop and signaling the body to begin anew. Bleeding typically lasts 3-7 days, with the heaviest flow usually occurring in the first 2-3 days.

Follicular Phase (Days 1-13): Overlapping with menstruation, this phase involves the development of follicles in the ovaries. The pituitary gland releases follicle-stimulating hormone (FSH), which stimulates the ovaries to produce 5-20 follicles, each containing an immature egg. Usually, only one follicle will mature fully. As the follicle develops, it produces estrogen, which thickens the uterine lining in preparation for a potential pregnancy.

Ovulation (Day 14): Around the middle of the cycle, rising estrogen levels trigger a surge of luteinizing hormone (LH), causing the mature follicle to release its egg into the fallopian tube. This is ovulation. The egg remains viable for fertilization for approximately 12-24 hours. This is the most fertile time of the cycle, and sperm can survive in the reproductive tract for up to 7 days, creating a fertile window of about 6 days each cycle.

Luteal Phase (Days 15-28): After ovulation, the empty follicle transforms into the corpus luteum, which produces progesterone and some estrogen. These hormones maintain the thickened uterine lining. If the egg is not fertilized, the corpus luteum breaks down around day 22-24, hormone levels fall, and the cycle begins again with menstruation.

What Happens in the Body During the Menstrual Cycle?

During the menstrual cycle, the ovaries release an egg while the uterus prepares a thickened lining to potentially receive a fertilized egg. Hormones including estrogen, progesterone, FSH, and LH coordinate this process. If pregnancy doesn't occur, hormone levels drop, the uterine lining sheds, and menstruation begins.

The menstrual cycle is orchestrated by a sophisticated communication system between the brain and the reproductive organs. The hypothalamus, a region of the brain, releases gonadotropin-releasing hormone (GnRH), which signals the pituitary gland to produce FSH and LH. These hormones then act on the ovaries, triggering egg development and hormone production. This feedback system ensures that each phase of the cycle occurs in the correct sequence.

The ovaries are the primary reproductive organs where eggs (ova) develop and are stored. Each ovary contains thousands of follicles, each housing an immature egg. At birth, the ovaries contain approximately 1-2 million eggs, but this number decreases with age. By puberty, about 300,000-400,000 eggs remain, and only about 400-500 will actually be released through ovulation during a person's reproductive years.

Each month, several follicles begin developing, but typically only one becomes the "dominant" follicle that will release a mature egg. As this dominant follicle grows, it produces increasing amounts of estrogen. This hormone has widespread effects throughout the body, including thickening the uterine lining, increasing cervical mucus production (which becomes more fluid and favorable to sperm), and affecting mood, energy levels, and even skin appearance.

When estrogen reaches a critical level, it triggers the LH surge that causes ovulation. The release of the egg from the ovary is sometimes accompanied by mild cramping called "mittelschmerz" (German for "middle pain"), which some people can feel on one side of their lower abdomen. This can actually be a helpful sign for tracking ovulation.

The uterus, or womb, is the organ that would house a developing pregnancy. Its lining, the endometrium, undergoes remarkable changes throughout the cycle. During the follicular phase, estrogen causes the endometrium to thicken and develop a rich blood supply. After ovulation, progesterone from the corpus luteum further transforms the lining, making it more receptive to a fertilized egg (this is called the "secretory phase" of the endometrium).

If fertilization and implantation do not occur, the corpus luteum degenerates, progesterone and estrogen levels fall sharply, and the blood vessels supplying the endometrium constrict. This triggers the shedding of the uterine lining – menstruation – and the cycle begins again.

How Long Is a Normal Menstrual Cycle?

A normal menstrual cycle lasts between 21-35 days, with an average of 28 days. The period itself typically lasts 3-7 days. Cycle length can vary from month to month, and variation of up to 7-9 days between cycles is considered normal. Only about 13% of cycles are exactly 28 days.

Understanding what constitutes a "normal" cycle is essential for recognizing when something might be amiss. The menstrual cycle length is measured from the first day of menstrual bleeding in one cycle to the first day of bleeding in the next cycle. While 28 days is often cited as the standard, research shows substantial variation in what's healthy and normal.

A large study analyzing over 600,000 menstrual cycles found that the average cycle length was 29.3 days, with a standard deviation of about 7.5 days. This means that cycles anywhere from 21 to 35 days are within the normal range. Additionally, cycle length often varies from month to month – having cycles that differ by up to 7-9 days is completely normal and doesn't necessarily indicate a problem.

The length of your period – the actual days of bleeding – is somewhat independent of your overall cycle length. Most periods last between 3-7 days, with bleeding typically heaviest in the first 2-3 days. It's common for bleeding to start heavier and gradually become lighter, though some people experience the opposite pattern.

Several factors can influence cycle length and regularity. Age is perhaps the most significant: cycles tend to be irregular for the first few years after menarche as the body establishes its pattern. They often become more regular in the twenties and thirties, then may become irregular again in the perimenopause years leading up to menopause.

Other factors that can affect cycle length include stress, significant weight changes, excessive exercise, certain medical conditions (such as polycystic ovary syndrome or thyroid disorders), and some medications. Travel across time zones and disrupted sleep patterns can also temporarily affect cycle timing.

What Are Common Symptoms During the Menstrual Cycle?

Common menstrual cycle symptoms include menstrual cramps, breast tenderness, bloating, mood changes, fatigue, and changes in appetite. Many people also experience premenstrual syndrome (PMS) in the days before their period. Most symptoms are mild and manageable, but severe symptoms should be discussed with a healthcare provider.

Throughout the menstrual cycle, hormonal fluctuations can cause a variety of physical and emotional symptoms. While these experiences vary widely among individuals, understanding common patterns can help you anticipate and manage cycle-related changes. It's important to note that having symptoms is normal, but symptoms that significantly interfere with daily life warrant medical evaluation.

Menstrual cramps, medically known as dysmenorrhea, are among the most common period-related symptoms, affecting up to 84% of people who menstruate. Cramps are caused by prostaglandins – hormone-like substances produced by the uterine lining that trigger muscle contractions to help shed the endometrium. These contractions can cause cramping pain in the lower abdomen, which may radiate to the lower back and thighs. Cramps are typically worst in the first 1-2 days of the period and gradually improve.

Primary dysmenorrhea refers to normal menstrual cramps without an underlying medical cause. Secondary dysmenorrhea involves pain caused by conditions such as endometriosis, fibroids, or adenomyosis. While mild to moderate cramps are normal, pain that doesn't respond to over-the-counter medication, causes you to miss work or school, or progressively worsens should be evaluated by a healthcare provider.

Premenstrual Syndrome (PMS)

PMS describes a collection of symptoms that occur in the luteal phase (typically 1-2 weeks before menstruation begins) and resolve shortly after the period starts. Up to 90% of people who menstruate experience at least some PMS symptoms, though severity varies widely. Symptoms can be physical, emotional, or behavioral.

Physical PMS symptoms may include breast tenderness and swelling, bloating and fluid retention, headaches or migraines, fatigue, food cravings (particularly for carbohydrates and sweets), acne flares, and digestive changes such as constipation or diarrhea. Emotional and behavioral symptoms can include irritability, mood swings, anxiety, depression, difficulty concentrating, and changes in sleep patterns.

For most people, PMS symptoms are mild and manageable. However, approximately 5-8% of people experience a severe form called premenstrual dysphoric disorder (PMDD), which causes significant emotional disturbances that interfere with daily functioning. PMDD is a recognized medical condition that benefits from professional treatment, which may include medication and lifestyle modifications.

Managing Menstrual Symptoms

Many effective strategies exist for managing common menstrual symptoms. For cramps, over-the-counter pain relievers such as ibuprofen or naproxen (NSAIDs) work best when taken at the first sign of cramping, as they reduce prostaglandin production. Heat applied to the lower abdomen (via heating pad or hot water bottle) can also provide significant relief by relaxing the uterine muscles.

Regular physical activity has been shown to reduce both menstrual pain and PMS symptoms. Exercise releases endorphins, which are natural pain relievers, and may help regulate hormone levels. Even gentle activities like walking, yoga, or swimming can be beneficial. Dietary modifications may also help – reducing salt intake can minimize bloating, while limiting caffeine and alcohol may improve mood-related symptoms.

What Is Ovulation and When Does It Occur?

Ovulation is the release of a mature egg from the ovary, typically occurring around day 14 of a 28-day cycle (about 14 days before your next period). Signs of ovulation include changes in cervical mucus, mild cramping, and a slight rise in body temperature. The egg can be fertilized for about 12-24 hours after release.

Ovulation is the pivotal event of the menstrual cycle – the moment when a mature egg is released from the ovary and becomes available for fertilization. Understanding ovulation is important not only for those trying to conceive but also for anyone seeking to understand their body's rhythms and fertility window.

The process of ovulation is triggered by a surge in luteinizing hormone (LH) that occurs when estrogen levels reach a critical threshold during the follicular phase. This LH surge causes the mature follicle to rupture, releasing the egg into the fallopian tube. Ovulation typically occurs 24-36 hours after the LH surge begins.

While ovulation is often said to occur on "day 14" of the cycle, this is only true for a textbook 28-day cycle. In reality, ovulation timing varies considerably. What remains relatively constant is that ovulation occurs approximately 14 days before the start of the next period (this is called the luteal phase length). So, in a 30-day cycle, ovulation might occur around day 16; in a 26-day cycle, it might occur around day 12.

After release, the egg travels through the fallopian tube toward the uterus. It remains viable for fertilization for only about 12-24 hours. However, because sperm can survive in the female reproductive tract for up to 5-7 days, the fertile window – the days during which intercourse could result in pregnancy – spans about 6 days: the 5 days before ovulation and the day of ovulation itself.

Signs and Symptoms of Ovulation

Many people can identify when they're ovulating by paying attention to certain body signals. Cervical mucus changes are one of the most reliable indicators. In the days leading up to ovulation, cervical mucus increases in quantity and becomes clearer, more slippery, and stretchy – often compared to raw egg whites. This "fertile quality" mucus helps sperm survive and travel to meet the egg.

Some people experience mittelschmerz, a mild pain or cramping sensation on one side of the lower abdomen around the time of ovulation. This is caused by the follicle stretching the ovary before rupture or by fluid released during ovulation irritating the abdominal lining. The sensation may last from a few minutes to a day or two.

Basal body temperature (BBT) – your temperature at complete rest – shows a characteristic pattern around ovulation. After ovulation, progesterone causes BBT to rise by about 0.2-0.5°C (0.4-1°F) and remain elevated until the next period begins. By tracking BBT daily, you can confirm that ovulation has occurred, though this method only identifies ovulation after the fact.

Other potential ovulation signs include increased libido, breast tenderness, light spotting, heightened sense of smell, and subtle changes in the cervix position (it becomes higher, softer, and more open around ovulation). Ovulation predictor kits, available over-the-counter, can detect the LH surge and predict ovulation 24-36 hours in advance.

Can You Get Pregnant During Your Period?

Yes, it is possible to get pregnant during your period, though the probability is lower than at other times. Sperm can survive in the uterus for up to 7 days, so if you have a shorter cycle or early ovulation, sperm from intercourse during your period could still be present when ovulation occurs. No time during the menstrual cycle is completely "safe" from pregnancy risk.

Many people believe that menstruation is a "safe" time when pregnancy cannot occur. While it's true that the probability of conception is lower during menstruation, it is not zero. Understanding why requires knowledge of both ovulation timing and sperm survival.

Pregnancy occurs when sperm fertilizes an egg. For this to happen, viable sperm must be present in the fallopian tube when the egg is released. While eggs only survive 12-24 hours after ovulation, sperm are much hardier – they can survive in the female reproductive tract for up to 7 days under optimal conditions (though 3-5 days is more typical).

Consider a person with a 24-day cycle who ovulates around day 10. If they have intercourse on day 4 (still during their period), some sperm could potentially survive until day 10 and fertilize the released egg. Similarly, if someone has irregular cycles and ovulates earlier than expected, conception from intercourse during menstruation becomes possible.

It's also worth noting that bleeding doesn't always indicate menstruation. Some people experience light bleeding around ovulation (ovulation spotting), which could be mistaken for an early or light period. Intercourse during this bleeding could obviously result in pregnancy since it coincides with the most fertile time.

For these reasons, if preventing pregnancy is a priority, it's important to use contraception throughout the entire cycle, not just during "fertile" days. Methods like hormonal contraceptives (pills, patches, rings, implants, hormonal IUDs), copper IUDs, or barrier methods provide protection regardless of cycle timing.

What Menstrual Products Are Available?

Common menstrual products include pads (disposable and reusable), tampons, menstrual cups, menstrual discs, and period underwear. Each has advantages and disadvantages regarding convenience, comfort, cost, environmental impact, and activity level. The best choice depends on personal preference, flow heaviness, and lifestyle.

Today, there are more options than ever for managing menstrual bleeding. Understanding the different products available can help you find what works best for your body, lifestyle, and values. Many people use different products at different times – for example, pads at night and tampons or a cup during the day.

Pads (sanitary napkins) are absorbent materials worn inside underwear to catch menstrual blood externally. They come in various sizes and absorbencies, from panty liners for light flow to overnight pads for heavier bleeding. Disposable pads are convenient and require no insertion, making them a common choice for those new to menstruation. Reusable cloth pads are available as an eco-friendly alternative – they're washed and reused, reducing waste and long-term costs.

Tampons are inserted into the vagina to absorb menstrual blood internally before it leaves the body. They're available in different absorbencies and with or without applicators. Tampons allow for swimming and other activities without worry about visible protection. It's important to change tampons every 4-8 hours and use the lowest absorbency needed to reduce the risk of toxic shock syndrome (TSS), a rare but serious bacterial infection.

Menstrual cups are reusable, flexible cups usually made of medical-grade silicone that are inserted into the vagina to collect rather than absorb menstrual blood. A single cup can last up to 10 years with proper care, making them economical and environmentally friendly. Cups can be worn for up to 12 hours before emptying, rinsing, and reinserting. There's a learning curve to insertion and removal, but many people find them very comfortable once mastered.

Menstrual discs are similar to cups but sit in a different position (at the base of the cervix rather than lower in the vaginal canal). They can sometimes be worn during intercourse without being felt by partners. Both disposable and reusable versions are available.

Period underwear features built-in absorbent layers that absorb menstrual blood. They look and feel like regular underwear but can replace or supplement other menstrual products. They're available in various absorbency levels and styles and are reusable after washing.

When Should You See a Doctor About Your Period?

See a doctor if your periods last more than 10 days, you need to change pads/tampons every 1-2 hours, you have severe pain not relieved by OTC medication, you miss periods for 6+ months (not pregnant), or your cycle becomes significantly more irregular. Bleeding between periods or after menopause also requires evaluation.

While variation in menstrual cycles is normal, certain changes or symptoms warrant medical attention. Being aware of these warning signs helps ensure that potential problems are identified and addressed early. Your period is often referred to as a "vital sign" of overall health because menstrual changes can indicate underlying medical conditions.

Heavy menstrual bleeding (menorrhagia) is one of the most common reasons to seek care. Signs include needing to change pads or tampons every 1-2 hours for several hours in a row, needing to use double protection (pad plus tampon), passing blood clots larger than a quarter, or bleeding that lasts more than 7 days. Heavy bleeding can lead to iron deficiency anemia, causing fatigue, weakness, and other symptoms.

Severe menstrual pain that doesn't respond to over-the-counter medications or interferes with daily activities should be evaluated. While some cramping is normal, debilitating pain may indicate conditions such as endometriosis (where tissue similar to the uterine lining grows outside the uterus), adenomyosis (where this tissue grows into the uterine muscle), or uterine fibroids (noncancerous growths in the uterus).

Irregular or absent periods can have various causes. If your period suddenly becomes much more irregular than usual, or if periods stop completely for 6 months or more (when not pregnant, breastfeeding, or approaching menopause), this warrants investigation. Conditions such as polycystic ovary syndrome (PCOS), thyroid disorders, pituitary problems, or premature ovarian insufficiency may be involved.

Bleeding between periods (intermenstrual bleeding) or spotting should be discussed with a healthcare provider, especially if it's a new occurrence. While it's sometimes caused by hormonal fluctuations or contraceptive use, it can also indicate infections, polyps, or rarely, cervical or uterine cancer.

Bleeding after menopause is always abnormal and requires prompt evaluation to rule out serious causes including endometrial cancer.

Can You Choose to Skip Your Period?

Yes, you can safely skip or eliminate your period using hormonal contraceptives. Continuous or extended-cycle birth control pills, hormonal IUDs, implants, and injections can all reduce or stop menstruation. This is medically safe and may be beneficial for those with painful periods, heavy bleeding, or menstrual-related conditions.

You do not need to have a period every month to be healthy. In fact, the monthly period experienced by people on combined hormonal contraceptives (pills, patches, rings) is not a true period at all – it's a withdrawal bleed that occurs during the hormone-free interval and serves no medical purpose. It was originally included in pill design to mimic a natural cycle, not for health reasons.

Many people choose to reduce or eliminate their periods for various reasons: severe menstrual cramps, heavy bleeding, conditions like endometriosis or menstrual migraines, or simply personal preference and convenience. For example, athletes, travelers, or those in professions where managing periods is difficult may prefer to skip menstruation.

Methods to reduce or skip periods include:

Continuous combined hormonal contraception involves taking active pills (or using patches/rings) continuously without the placebo week, preventing the withdrawal bleed. This is safe for most people and can be done indefinitely. Some breakthrough bleeding may occur initially but usually decreases over time.

Hormonal IUDs (such as those releasing levonorgestrel) often reduce menstrual bleeding significantly, and about 20% of users stop having periods altogether after one year of use. The progestin thins the uterine lining, reducing or eliminating bleeding.

The contraceptive implant and injection (Depo-Provera) also frequently cause lighter periods or amenorrhea (absence of periods). Effects vary by individual, with some people experiencing irregular spotting, especially initially.

For those not using hormonal contraception, medications like norethisterone can be prescribed to delay a specific period (for example, for a vacation), though this is a short-term solution rather than ongoing period suppression.

Gender Dysphoria and Menstruation

Some people experience psychological distress related to menstruation, particularly if it conflicts with their gender identity. This is called gender dysphoria. Menstrual suppression using hormonal methods can help reduce this distress. Healthcare providers can offer supportive care and discuss options for managing or eliminating periods.

For some individuals, menstruation can be a source of significant psychological distress, particularly when it conflicts with their sense of gender identity. This experience is an aspect of gender dysphoria – discomfort or distress arising from a mismatch between a person's gender identity and their body's characteristics.

Transgender men, nonbinary individuals, and others whose gender identity differs from their sex assigned at birth may find menstruation distressing because it emphasizes physical characteristics that don't align with their identity. The monthly reminder of biological characteristics can negatively impact mental health and well-being.

Fortunately, effective options exist for those who wish to reduce or eliminate menstruation. Hormonal methods described in the previous section – including continuous contraceptives, hormonal IUDs, implants, and injections – can significantly reduce or stop periods. For those pursuing gender-affirming hormone therapy (testosterone), periods typically stop within a few months of starting treatment.

Healthcare providers should offer affirming, nonjudgmental care to all patients experiencing menstrual-related distress. If you're struggling with how menstruation affects your sense of self or mental health, speaking with a healthcare provider can help you explore options and find appropriate support. Mental health professionals specializing in gender identity can also provide valuable support.

Can You Have Sex During Your Period?

Yes, it's safe to have sex during your period if you and your partner are comfortable with it. Some people find period sex relieves cramps due to orgasm-induced muscle relaxation and endorphin release. Using protection is still important to prevent STIs, and pregnancy is still possible though less likely.

Many people wonder whether sexual activity during menstruation is safe or advisable. The straightforward answer is yes – there's nothing medically wrong with having sex during your period. The decision is entirely personal and depends on comfort levels, preferences, and practical considerations.

Some potential benefits of period sex include natural lubrication from menstrual fluid, and for some, orgasms can help relieve menstrual cramps. Orgasm causes the uterus to contract and then relax, which may ease cramping. Additionally, the release of endorphins during orgasm acts as a natural pain reliever and mood booster.

Practical considerations include the potential for messiness, which can be managed with towels, shower sex, or menstrual discs (which can be worn during penetrative sex). Communication with partners about comfort levels is important.

Important safety notes: STIs can still be transmitted during period sex – in fact, the presence of blood may slightly increase transmission risk for some infections. Using condoms or other barrier methods remains important for STI prevention. And as discussed earlier, pregnancy is possible during your period, so contraception should be used if avoiding pregnancy.

If using tampons or menstrual cups, these should be removed before vaginal penetration. Menstrual discs are specifically designed to allow penetrative sex while wearing them.