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It started out as a bit of a drunken joke between a couple of friends who couldn't understand why so few men had moustaches anymore.
In a bid to bring the top lip topiary back, they managed to convince 30 guys to spend a month trying to cultivate the best tash they could - there was no fundraising, no charity. It was just a bunch of friends doing it for a laugh.
The following year they managed to get more than 400 men on board, but this time decided to try and raise a bit of money - A$54,000 in fact - for research into prostate cancer.
The next year it rolled on to over 9,000 men and A$1.2 million. The moustache movement was...growing.
And now - 15 years since that joke - the Movember Foundation has snowballed into a global phenomenon, with more five million men taking part across 21 countries.
Together they have managed to raise more than A$750 million to help fight some of the biggest issues that affect men's health - prostate cancer, testicular cancer, mental health, and suicide prevention.
It may not seem like a big deal - growing a bit of lip fuzz for a few weeks - but the genius is in its simplicity.
It's not like the usual challenge, like completing a marathon or playing a sport - you don't have to be exceptionally fit or talented, everyone can take part.
In fact, you don't really have to do anything. Just let it grow.
So why is Movember still important?
Across the world, 5.6 million men are currently living with prostate cancer and in the UK alone it claims the life of 10,000 men a year - one every 45 minutes.
Testicular cancer is the most common cancer among young men in the UK, with more than 2,000 people diagnosed with the disease every year.
Suicide is the biggest cause of death to men under the age of 50. That statistic alone is frightening.
Last year, more than 5,000 people took their own lives in the UK - with 75% of those being men.
The Movember Foundation says: "Globally, the rate of suicide is alarmingly high, particularly in men. Around the world, on average we lose a man to suicide every minute of every day. Six out of 10 suicides are men. Too many are toughing it out and struggling alone.
"We have to take action to improve mental health and reduce the rate of male suicide."
So if you're getting involved this year, what are the Movember rules?
From today, every Mo Bro that has signed up to take part in the challenge must spend the next 30 days maintaining his lip hair - and you are encouraged to get creative. The wackier the style the better.
But this is a strictly tash only party, guys. That means no beards, so make sure you've had a clean shave before starting the month-long challenge.
It's not just for men either; women are encouraged to don their own fake moustache during fun runs to raise money for the cause.
And if you manage to make it to the finish line, take a photograph of the finished article and share it online, with your friends and family, and anyone who dug deep to sponsor you.
You will have helped to raise a ton of cash to help millions of people across the world fight their battles - and you will have become part of a community of bros for life.
Now if that's not worth looking ridiculous for a few weeks, I don't know what is.
For more information visit https://uk.movember.com/?home
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