I'm surprised precisely every time I get my period. 

Despite it arriving roughly once a month for the last 15 years, it's always a shock. But when it comes - usually staining a perfectly good pair of undies - there's something oddly... comforting about it.

It reminds me of the weird and wonderful inner workings of the human body, ticking away silently as I'm going about my day-to-day life. How does it know it's been about a month since my last period? How does it know how much blood to let out?

It's very clever, that's how. 

So it's time we celebrated it, with all the facts you (probably) didn't know: 

1. On average, people who menstruate will menstruate for TEN YEARS of their lives. TEN. YEARS.

No wonder women tend to live longer than men. We bloody deserve it. 

With girls typically beginning their period between 10 and 18, and continuing to menstruate until somewhere between 45 and 55, women have an average of around 500 periods in their lifetime. 

If the average length of a period is seven days, that's 3500 days of bleeding - almost 10 years. 

Considering you're going to spend a decade of your life on your period, it's worth looking into issues that make it particularly uncomfortable - like severe period pain. A visit to the GP can help determine whether it's normal, or whether there are further tests that can look into problems like endometriosis. 

2. Menstrual products have an environmental toll.

This one's pretty depressing.

Over our lifetimes, people who menstruate will use somewhere between 5000 and 14,000 pads and tampons. That's a huge toll on the environment. 

Luckily, there are some brands who have designed their products specifically to tackle this issue, meaning you can go about your life without worrying about the ecological footprint your period is leaving behind. 

If you're set on pads and tampons (and not a menstrual cup or period-proof underwear), look for 100 per cent cotton products, and sustainable packaging, from a brand like Veeda, an affordable, safe eco-friendly option that has just launched in Australia.

Veeda tampons are made only with 100 per cent natural cotton and have no chemicals, no synthetics, and no dyes. 

Their packaging is also biodegradable, so doesn't require special disposal.

As well as being environmentally friendly, Veeda tampons also provide a lower risk to toxic shock syndrome (TSS), irritation, and allergic reactions. They're hypoallergenic and fragrance-free, and they're dermatologically and gynaecologically tested. So they're a win-win, for the environment and for you.

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3. Your period gets worse when it's cold.

If you've been noticing your period being worse lately, you might not be imagining it. 

Research shows that winter can have an impact on the length of your period, as well as the low moods associated with it. 

One 2011 study found that mentrual cycles are influenced by sunshine, with women on average having shorter periods during summer, and longer periods during winter. 

You might notice your moods being more affected, too.

The symptoms of premenstrual dysphoric disorder (PMDD), however, are most likely influenced by the lifestyle factors that come with the change of season. 

When it's warm, we tend to move more, and spend more time outside. Women who exercise regularly are less likely to suffer from severe PMDD. 

Image: Getty.

4. You don't need to have a 'period' whilst on the Pill.

There's actually a slightly... disturbing story behind this. 

Since the introduction of the contraceptive pill in the '50s, women have, for the most part, stuck with what the packaging tells us: take one hormonal pill every day for 21 days, then take a placebo pill for the next seven.

But it turns out the sugar pills don't actually serve any purpose whatsoever. There's no need for a 'fake period', and in fact, there's no issue with taking the Pill every day of the month without having the 'seven-day break'.

Guidelines from the Faculty of Sexual And Reproductive Healthcare (FSRH) state there are no health benefits to having 21-day cycles on the combined pill. When you look at the context, there's actually a historical reason for the sugar pills - not a scientific one. 

John Rock, the Catholic gynaecologist who was involved with the development of the Pill, thought the Catholic Church would be much more likely to approve the combined contraceptive pill if it mimicked the natural menstrual cycle.

Cool.

5. The average age someone gets their first period has dropped from 17 to 12. 

At the turn of the 20th century, the average age of onset for a girl's first period was 16 or 17. 

Today, that number is closer to 12 or 13. 

There's evidence that boys, too, are reaching puberty earlier, and interestingly, the science isn't clear on why. 

Some theories include increased body mass index in children, and nutrition or hormone influences in our diets. 

6. Sleeping with a night light can regulate your cycle.

Sorry... what?

Decades of research shows that a bedside light can shorten and regulate women's menstrual cycles, for those who have long and irregular periods. 

More broadly, there's evidence that disrupted sleep patterns are associated with disturbances in menstrual function, with shiftworkers more likely to report that their periods are irregular, and longer. 

These findings may have important implications for contraception and infertility.

So next time you're feeling a bit grumpy about your period, remember that while it's inconvenient, it's also very bloody clever.