Reason why Cristiano Ronaldo paints his toenails black is genius as social media post goes viral

Cristiano Ronaldo stunned fans when it emerged that he paints his toenails black - but there is a very good reason for it.

On Sunday, Ronaldo, fresh from winning the Nations League for a second time with Portugal, Ronaldo was in the gym with his 14-year-old son Cristiano Jr as they flexed their muscles after an intense workout.

The Instagram post, which garnered 17 million likes, received plenty of comments - with Ronaldo's former teammate Patrice Evra pointing out that his son is "getting taller" than his old man.

However, many others observed that Ronaldo, standing in his bare feet, had black toenails.

Plenty wondered whether it was a fashion statement from Ronaldo, following a type of trend that is common in emo rock brands.

But there is a genuine explanation for why Ronaldo, who is meticulous about his preparation and routine, has black nail polish.

Why does Cristiano Ronaldo wear black nail polish?

According to German outlet BILD, the 40-year-old paints his nails to prevent fungi and bacteria as an athlete, he spends a lot of time in sweaty shoes and boots.

Cristiano Ronaldo posted a picture of him and his son on Instagram. Image: Getty

Through the polish, a protective layer is created which hardens the toenails and makes it harder to be cracked.

Ronaldo is arguably the highest-profile person to follow the method but plenty of sports people are also prone to it, specifically those who compete on the track and boxing and MMA fighters.

It's believed Mike Tyson painted his nails in the peak of his boxing career when he was world heavyweight champion, while former UFC middleweight champion Israel Adesanya is a more recent member of the black nails club.

Ronaldo is still doing the business 23 years on from his professional debut and it's no secret that his strict routine and healthy lifestyle is a huge factor in his longevity.

The five-time Ballon d'Or winner takes great pride in what he eats as he has a high-protein diet which avoids sugars - with his favourite dish being Bacalhau a Bras - a Portuguese dish made up of salted cod, onions, potatoes and eggs.

He is into cryotherapy to aid his recovery, while rest is also important as Ronaldo takes around five short naps of an hour-and-a-half each time throughout the day in a sleeping in a fetal position.

Working with sleep coach Nick Littlehales when he was at Real Madrid, it's claimed short bursts of sleep works as a better method than sleeping for eight hours in one go at night.