The one skincare product that will save you thousands over your lifetime.

Reese Witherspoon, Julianne Moore and Nicole Kidman all swear by it – and this skincare product can cost you as little as $10 but end up saving you thousands of dollars in the long run.

We’re talking about sunscreen. And before you roll your eyes at the advice we’re sure you’ve heard dozens of times before, hear us out. Because not using sunscreen could just be your biggest regret. Well, beauty-related at least.

It is for Mamamia executive editor and experienced beauty writer Leigh Campbell.

Despite writing about beauty for work, Leigh didn’t wear much sunscreen in her younger years and ended up with the pigmentation and fine lines on her face to show for it.

“It wasn’t until I reached my early 30s that I started to see the cumulative damage done by the sun in my teens and 20s,” she said.

“I wish I had listened to my mother when she constantly told me to wear sunscreen.”

Leigh said she's since spent "countless amounts of money" on expensive products and treatments to try and reverse the pigmentation which has appeared as the result of sun exposure.

"I cringe at the money I could have saved if I had just worn sunscreen - it really is the most effective and affordable anti-ageing skincare product."

It's an all too common complaint of people now spending hundreds, if not thousands of dollars every year on anti-wrinkle creams and serums, as well as procedures like Botox.

And while no one can avoid developing wrinkles, any dermatologist will tell you sun exposure is the number one cause of skin ageing.

For that reason, Dr Michael Freeman, lead dermatologist at The Skin Centre, told Mamamia in February that "sunscreen should play a vital role in your anti-ageing skin regime".

Meanwhile, Priceline pharmacist Amy Sabatini said: "Using an SPF50+ sunscreen is extremely important in protecting us against sun exposure and preventing the harmful effects of UV rays on our skin."

Both UVA and UVB rays - which any high SPF (30+ or more) broad-spectrum sunscreen will protect against - are harmful. According to the Cancer Council, UVA rays penetrate deeply into the skin causing genetic damage to cells and photo-ageing  - which results in wrinkles and blotchiness.

Now, this is where we have to put a big fat disclaimer in: There is nothing wrong with having wrinkles - or freckles, or age spots. And if you are not worried one bit about seeing these on your face, that's great.

But there's another huge reason to use sun protection - and it's just a tiny bit more important than how you look or how much money you have. We're talking about skin cancer of course, and how sun exposure is its leading cause.

Hugh Jackman knows all about this - having had not one, but six cancerous moles removed from his face in the past few years.

In November 2013, doctors first discovered a mole on the actor's nose was actually basal cell carcinoma - which was removed immediately. Since then, the 50-year-old has had to have five more non-melanoma cancerous moles removed, with the most recent one last February.

His message to fans is simple - and it's the same advice you'll hear from anyone who's paying for their past carefree ways today: "Use sunscreen please."

Want to know which kind of sunscreen to use? Check out our story on physical vs chemical sunscreen or listen to You Beauty.