What Causes Heavy Periods: Medical & Lifestyle Factors

If you or your daughter are dealing with periods that feel like too much, you are not alone. Heavy periods are one of the most common things women and girls experience, and yet so many of us just quietly put up with them thinking it is normal. Sometimes it is just how your body works. But sometimes there are real reasons behind it that are worth knowing about.

Let's talk through what causes heavy periods, from body stuff to lifestyle factors, so you actually feel informed and not just overwhelmed.

First, What Even Counts as Heavy?

Heavy is pretty subjective, right? But some signs that your flow is on the heavier side include soaking through a pad or tampon every hour or two, passing large clots, bleeding for more than seven days, or just feeling exhausted and wiped out during your period. If that sounds familiar, it is worth paying attention to.

Hormones Are Usually the Starting Point

One of the most common reasons behind what causes heavy periods comes down to hormones. Specifically, the balance between oestrogen and progesterone. When oestrogen is higher relative to progesterone, the lining of the uterus builds up more than usual. When your period starts, there is simply more to shed.

This is really common in two life stages. One is the early years of periods, which is exactly why your tween daughter might have unpredictable or heavier flows in her first couple of years. Her body is still figuring out the rhythm. The other is perimenopause, which is that phase before periods stop entirely. If you are in your late 30s or 40s, this might be what is going on for you.

Conditions That Can Play a Role

Sometimes the body has something specific going on that makes periods heavier. A few of the more common ones include:

Fibroids. These are non-cancerous growths in or around the uterus. They are really common, especially in women in their 30s and 40s, and they can cause significantly heavier periods along with more cramping.

Endometriosis. This is where tissue similar to the uterine lining grows outside the uterus. It can cause very painful and heavy periods. It often goes undiagnosed for years, so if your periods are both heavy and really painful, it is worth bringing up with your GP. We've written more about endometriosis if you want to understand it better.

Adenomyosis. Similar to endometriosis but the tissue grows into the wall of the uterus itself. Heavy, crampy periods are a classic sign.

Thyroid issues. Your thyroid affects so many things in your body, including your cycle. An underactive thyroid in particular can lead to heavier periods.

Polycystic ovary syndrome (PCOS). This can cause irregular periods, and when a period does arrive after a longer gap, it can be heavier than usual.

None of this is meant to send you into a spiral. It is just useful to know that what causes heavy periods is not always mysterious. There are often real answers, and real support available once you know what you are dealing with.

Lifestyle Factors That Can Make Periods Heavier

It is not always a medical condition. Sometimes day-to-day life plays a part too.

Stress. Chronic stress messes with your hormones in a big way. High cortisol levels can affect the hormonal balance that regulates your cycle. So yes, a particularly rough few months at work or home can actually show up in your period.

Weight changes. Fat cells produce oestrogen. Significant weight gain can increase oestrogen levels in your body, which can contribute to a heavier flow. On the flip side, being underweight can cause its own hormonal disruptions.

Intense exercise. While regular movement is great for period health overall, very high levels of intense training can throw your cycle off. Some athletes notice changes in flow as a result.

Diet. A diet low in iron can make you more fatigued during a heavy period, which makes everything feel worse. Some research also suggests that foods high in inflammatory compounds can contribute to heavier, crampier periods.

Certain medications and supplements. Blood thinners and even some supplements like high-dose fish oil can affect how heavy your period is. Worth checking if you have recently started anything new.

What About Young Girls and Heavy Periods?

If your daughter is in her first couple of years of having periods and her flow seems intense, this is really common. Her cycle is still regulating. Hormones are all over the place and that is completely expected. That said, if she is soaking through protection very quickly, feeling faint, or really struggling, it is absolutely worth a chat with your GP. Some girls do have conditions like the ones listed above that can be identified and supported early.

The most important thing is that she has good period products that actually work for her flow, so she is not caught out at school, at sport, or on a sleepover. Having everything in one place makes a real difference to her confidence.

You Do Not Have to Just Put Up With It

Understanding what causes heavy periods is genuinely empowering. You are not being dramatic. Your experience is valid, and there is usually something behind it worth exploring. Whether it is hormones, a condition, or lifestyle factors, knowing more means you can have better conversations with your GP and make choices that actually help. For practical day-to-day strategies, here's how to stop heavy periods feeling so overwhelming, plus our wider guide to heavier menstrual periods.

And in the meantime, having the right period kit sorted takes at least one thing off your plate. If your daughter is just starting out, our First Period Tween Starter Kit has everything she needs to feel ready and confident, no matter how her flow shows up, and you can add the Tween Period Underwear 5-Pack if you want enough pairs to cover a heavier week. Because no girl should have to figure this out on her own.