We all know your period brings unwanted cramps, nausea, headaches and even hunger, but what about the things you don't know?
WHEN it comes to that time of the month, we all know what to expect.
Cramps, mood swings, probably a few tears and no doubt an intense craving for chocolate.
Some women are lucky enough to escape with just a few days of discomfort.
While others are doubled over in pain, facing a week of heavy bleeding. Your period can have a big impact on your body.
But what about the weird things that happen at that time of the month, that you had no idea about?
While on your period, there are a whole host of subtle changes that happen, here we reveal eight odd things you might notice...
1. Your voice gets deeper
Next month as THAT time approaches make a mental note to listen a bit more.
You might not notice it, but your voice will drop a few octaves, and sound deeper.
A recent study published in the journal PLOS One found women who are not using any form of hormonal contraception may experience fluctuations in the tone of their voice.
And the general tone is deeper.
It's thought to be down to changes in sex hormones that occur naturally at that time of the month so it is nothing to worry about.
Levels of oestrogen, the female sex hormone that keeps your voice a higher pitch, drop during the menstrual cycle, usually around the day of ovulation, which means your voice follows suit.
2. You can bleed from other parts of your body
It's caused by a condition called vicarious menstruation and occurs when you bleed from a mucosal membrane that's not your vagina during your time of the month.
Doctors in Illinois in the US once treated a 17-year-old girl who was crying bloody tears during the time of her period.
But don't worry, it's extremely rare so it's unlikely to happen to you.
3. Periods can trigger asthma
Like we don't have enough to worry about when that time of the month rolls around, your period can trigger asthma symptoms.
Women who has asthma may notice their symptoms are worse when they have their period thanks to perimenstrual asthma.
It's caused by fluctuations in the female sex hormone oestrogen, which may cause increased inflammation in the body.
Asthma is caused by inflammation in the lungs and airways, so if inflammation increases then asthma symptoms are likely to worsen.
Around 30 to 40 per cent of women with asthma report their symptoms get worse on their period.
4. Your jaw hurts
Some experts believe hormonal changes every month can leave to issues like inflammation of the gums and sensitive teeth.
And some women who suffer from pain in the jaw joint -notice it gets worse when they are on their period.
Women who take birth control pills, particularly ones that contain progesterone, may experienced inflammation of the gums, according to WebMD.
The hormone changes can also cause some women to develop red, swollen gums, swollen salivary glands, mouth ulcers and bleeding gums.
5. Everything hurts
OK, so maybe not everything hurts.
But your pain tolerance is usually a lot lower.
So that would explain why those cramps feel like they are impossible to handle, or why you can't seem to shake that headache or that nagging backache.
A 2003 study found that women rated pain "significantly higher" in the menstrual and premenstrual stage of their period than any other time of the month.
It is thought to be down, again, to hormone levels.
When your oestrogen levels are higher you're less sensitive to pain, but when your oestrogen levels drop so does your pain threshold.
6. You poop more
It's an embarrassing side effect that no one really wants to talk about.
But you've probably found that you poo more often when you're on your period.
And you may even experience diarrhoea.
That's because the chemicals your body produces to help your body shed the lining of your uterus - the one that gives you cramps - can also have the same effect on your bowel.
Also, your hormone changes make it easier for you to go.
7. It doesn't increase your risk of shark attack if you swim in the ocean - nor does it attract bears11
We all remember that scene in Anchorman when Brick says he read somewhere that periods attract bears because they can "smell the menstruation".
Or maybe you've been told that sharks can smell your period blood when you swim in the ocean, making you an appealing treat.
Don't worry, none of these are true - bears cannot smell menstruation, nor can sharks.
You're perfectly safe to go swimming, or camping, or hiking, or do anything outdoors when you have your period.
8. You don't sleep as well
There's a lot going on in your body when you have your period, so it makes sense if your sleep is a little disrupted.
After all, it can be hard to sleep when you're dealing with cramps, moods swings and a hunger nothing can satisfy.
According to the Sleep Health Foundation most women say their cycle effects how they sleep.
Your hormones are to blame, once again.
Hormonal changes during your time of the month affect the body's temperature control which affects sleep quality.
You are also likely to get less REM sleep that normal, which means your sleep cycles are disrupted and shorter.
9. You're clumsy... or clumsier than normal
There are several reasons for this.
The lack of sleep, mentioned above, affects your coordination.
But water retention can also affect your brain which can throw off your centre of gravity.
Not to worry though, it'll wear off once your period is done.
Just be extra careful when your playing sport, or doing anything that might require coordination.
10. Brain fog
On the topic of brains, your period can also give you brain fog.
It's the same thing that happens when you're pregnant.
Your body is basically firing around hormones left right and centre and your brain is left to marinade in it all, meaning you might find yourself forgetting things more than usual.
Low oestrogen levels during your period may also be responsible for decreased brain function.
But don't worry, it will all wear off once your period is over.
11. You burn calories like a machine
Finally, an upside!
The change in your hormone levels means you get more intensity out of your workouts.
The result? More food!
Although you shouldn't go overboard otherwise there was really no point in hitting the gym.
Exercise can also help ease the pain of cramps, so there is a plus side there too.