We’re taught that a “normal” period shows up every 28 days, on the dot. But real bodies don’t run on factory settings. Stress changes. Life happens. Hormones respond. So if your period feels different this month - earlier, later, heavier, lighter - take a breath. It doesn’t automatically mean something is wrong.
To help break it down properly (and calmly), we spoke to Dr Deborah Lee, GP and women’s health expert. Below, she answers the most common questions about cycle changes - what’s normal, what isn’t, and when to check in.
What are some of the most common, non-medical reasons someone’s cycle might change or become irregular?
Cycle changes are often rooted in life stages or lifestyle shifts rather than illness. Hormones are sensitive - especially during puberty, perimenopause, breastfeeding, stress, weight changes, or intense exercise. And irregular doesn’t automatically mean abnormal.
Here’s what Dr Deborah Lee explains:
What is a normal menstrual cycle?
A normal menstrual cycle means having a period every 28 days. However, there is a
normal range of 21-35 days – meaning some women have short cycles and some
have longer cycles.
The cycles may be
- regular e.g. every 21 days,
- or irregular, e.g. sometimes 21 days, sometimes 35 days
But you should see a pattern of cyclical bleeding.
When you are timing your cycle, day 1 is the first day of bleeding, and is the first day
of each new cycle.
The average period lasts 7 days - but some women bleed for fewer days shorter and
some for a day or two longer. All this is perfectly normal. Up to 25% of women have irregular cycles, meaning the cycle is less than 21 days or more than 35 days. Irregular cycles are more common around the time of puberty and in the run up to menopause. There are underlying physiological and hormonal reasons for this, and this is not the same as abnormal uterine bleeding (see below).
Reasons for irregular cycles
Puberty - The onset of a period depends on connections between the hypothalamus in the brain, the pituitary gland, also found in the brain, and the ovary. This is called the hypothalamo – pituitary - ovarian axis (HPO axis). This complex network releases hormones called gonadotrophins (GnRH, FSH and LH) that rise and fall once a month, resulting in the maturation and release of an egg.
In the early teenage years, the HPO axis is not fully developed, and ovulation often
does not occur every cycle. This means there is less oestrogen and progesterone
and less endometrial thickening (the lining of the womb), so that periods may be
missed, light or heavy.
Perimenopause – Ovarian failure occurs around the age of 51, but the ovaries start
to show signs of failure at any time over the age of 40. Periods may be light, heavy
or missed because the process of ovulation becomes less efficient and eventually
stops altogether.
Note that premature ovarian failure (POF) can occur at any age, even rarely in
teenagers. It is defined as having no periods for 12 months before the age of 40. It
affects 1-2% of women under age 40. This is an early menopause and is a serious
medical diagnosis.
Breastfeeding – When breastfeeding, levels of the hormone prolactin are high, and
this inhibits ovulation. A breastfeeding mother will usually not be having periods for
the first 6 months after delivery. However, this assumes she is fully breastfeeding
and not supplementing with bottles.
Once the baby starts weaning and breastfeeding begins to become less frequent, prolactin levels fall, the menstrual cycle slowly returns and ovulation can occur, resulting in the return of periods. But ovarian function may be sporadic to begin with giving irregular cycles.
Obesity – Having a BMI over 30 doubles the risk of having menstrual irregularities.
There is a strong overlap between polycystic ovarian syndrome (PCOS) and obesity.
But even obese women who do not have PCOS are more likely to fail to ovulate
regularly and may have irregular cycles and infertility.
In PCOS there can be problems with the HPO axis, as well as high levels of
androgens (testosterone) and insulin resistance. Many women with PCOS fail to
ovulate, and have few or infrequent light periods.
In general, obesity is linked to higher oestrogen levels, and oestrogen stimulates the
endometrium, increasing the likelihood of heavy, prolonged periods.
Hypothalamic hypogonadism – This occurs in those who are underweight, have
lost a lot of weight in a short time period, and in women who undergo excessive
exercise. It is commonly seen in women with eating disorders.
As a result of these extreme conditions, again, the HPO axis is disturbed. Fewer gonadotrophins (GnRH, LH and FSH) are produced and ovulation does not occur, or is sporadic, leading to
amenorrhoea (no periods) or infrequent periods.
Stress and anxiety - When your body is under threat from any kind of stress, the
brain perceives danger and activates the sympathetic nervous system (SNS). As a
result, adrenaline and cortisol levels are high, and the body goes into protective
mode. In addition, stress raises prolactin levels which also inhibits ovulation.
Altogether, this causes disruption of the HPO axis and impairs the natural production
of gonadotropin hormones. As a result, a woman may ovulate early, late or not all,
and periods may be early, late or missed altogether.
What this means for you
Your cycle is responsive. It reacts to age, stress, weight changes, breastfeeding, exercise, and more. That doesn’t make it broken - it makes it human.
How do stress, illness, travel, or lifestyle shifts affect ovulation and timing - especially in teens and young adults?
If your period shifted after exams, a breakup, long-haul travel, or even a nasty flu - you’re not imagining it. Hormones are tightly linked to stress signals and circadian rhythms.
Here’s Dr Deborah Lee:
Stress of any sort can affect the menstrual cycle. Travel can interfere with periods as
it disrupts Circadian rhythms. Even being in bed with the flu can alter your cycle.
Young people are particularly susceptible to stress because the HPO axis is not fully
developed until they are in their early twenties. In fact, stress not only causes
irregular cycles, it can cause heavy periods.
Stress levels are very high right now, with 1 in 4 young people having a mental
health condition. This could be due to the pressures of school/academia/student life,
bullying, social media pressures, work, financial, relationship, bereavement or any
other type of stress.
The takeaway
Your period can be a barometer for stress. Especially in teens and young adults, cycle changes are common while hormones are still settling. That doesn’t mean you should ignore symptoms - but it does mean you’re not alone.
At what point should someone check in with a healthcare professional, and what signs shouldn’t be ignored?
There’s a big difference between “different” and “concerning.” Tracking your cycle helps you spot patterns - and gives your GP useful information if needed.
Here’s Dr Deborah Lee’s guidance:
It’s a good idea to keep a note of the dates of your periods. Day 1 in the first day of
bleeding. Also record the date the period finished, and then the date the next period
starts and so on. You can write this in a diary, or you might like to use a period tracker app. Then you can show this to your GP if needed.
See your GP if you have irregular periods and -
- Your periods last longer than 7 days
-
You have other symptoms such as oily skin, acne, hair growth on your face
and problems with your weight - this is suggestive of PCO - Your periods are very heavy and painful
-
You are trying to become pregnant
(NHS)
Also,
- If you miss a period – do a pregnancy test if you could be pregnant.
- If the PT is negative, see your GP when you have missed 3 periods in a row
Take note - Always report to your GP if you have bleeding in between your periods or after sex.
This is abnormal uterine bleeding (AUB).
What is abnormal uterine bleeding?
Abnormal uterine bleeding (AUB) is also common. Around one third of women will
have at least one episode of AUB in a lifetime. AUB includes intermenstrual bleeding
(bleeding between periods), breakthrough bleeding (which occurs on hormonal
contraception), post coital bleeding (bleeding after sex) and heavy menstrual bleeding (HMB).
A woman will not know what is causing her erratic and abnormal bleeding and in all
these situations should see her GP.
Bottom line
Track first. Observe patterns. But if bleeding is unusually heavy, painful, between periods, or after sex - don’t wait. Get checked.
What’s one reassuring thing you wish more people knew when they’re worrying their period has “changed”?
When your cycle shifts, it’s easy to spiral. But there’s something powerful to remember: having periods means your hormones are active and working.
Here’s Dr Deborah Lee:
If you are having periods, this is a good thing. It means you have ovaries, eggs, a uterus and the hormones needed for ovulation. Women need oestrogen for good health. Having periods means oestrogen is being produced in the body.
The irregularity of the cycle is an indication something is not as it should be. This may be
a wake up call to needing to lower stress and make different lifestyle choices. Irregular periods are common in those with eating disorders. If you need help, why not call the Eating Disorders charity Beat by calling the Beat helpline on 0808 8010677.
All period problems can be managed one way or another. There is no need to suffer in silence. If you are concerned about your cycle and/or your periods, see your GP or visit the Sexual Health Clinic.
Note that any type of irregular bleeding including bleeding after sex and heavy periods can be cause by STIs such as chlamydia and gonorrhoea. If you notice a change in your cycle, go to the Sexual Health clinic for an STI screen.
All women should be strongly encouraged to have regular cervical smears. Abnormal
vaginal bleeding can be a sign of cervical cancer – although this is rare. Having regular smears helps prevent you from ever developing cervical cancer. Once you are called for a smear, around your 25th birthday, it’s very important to get this done. It’s just a few moments of being uncomfortable and it could save your life. If you are reading this and your smear test is overdue, please make an appointment.
Also, never assume if your periods are irregular that you can’t get pregnant! The body is a strange thing, and you could still ovulate at any time! If you don’t want to be pregnant, taking the combined pill for example, can regulate your cycle and prevent an unplanned pregnancy. The pill never causes a permanent loss of fertility, and when you stop taking it, your fertility will return straightaway. There are 15 methods of contraception and many of them can help improve your periods.
Final reassurance
A different period doesn’t automatically mean a dangerous one. Your cycle changes as you move through life. Sometimes it’s stress. Sometimes it’s age. Sometimes it’s your body asking for support.
And if something feels off? You deserve answers. Not anxiety. Track it. Notice it. Talk about it.
You’re not dramatic. You’re informed.
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