For Cristiano Ronaldo, it was a very on-brand family photograph.

Posing in a gym, the football icon flexed his muscular physique in trademark style, as his eldest son, Cristiano Junior, followed suit beside him.

The caption on X, where the Portuguese former Manchester United and Real Madrid forward posted the snap to his 115.5million followers, reads: ‘Tal pai tal filho’, or in English: ‘Like father, like son’. Indeed the teenager, who turns 15 this week and has already made a goal-scoring debut for Portugal Under-15s, seems to be following his father’s example of training hard.

But look carefully, beyond the familiar rippling abs and powerful leg muscles that have helped Ronaldo become a superstar, and you notice something else — the 40-year-old, who currently plays for Saudi Pro League club Al Nassr, has painted his toenails black.

So, is there a performance-related reason behind the five-time Ballon d’Or winner’s decision? Will this catch on?

Tal pai tal filho 😂 💪🏼 pic.twitter.com/tSfAwVQyof

— Cristiano Ronaldo (@Cristiano) June 15, 2025

It is not the first time Ronaldo has chosen to apply black nail varnish to his feet.

He has been pictured shoeless several times over the past couple of years, with the former Real Madrid star putting his painted toes on show while enjoying a sauna after training or when relaxing on holiday. But it is not a fashion choice. Instead, it appears to be another element of the legendary forward’s renowned dedication to his craft.

The black polish is a trend popularised by mixed martial arts (MMA) fighters, who do it to harden their toenails and prevent them from cracking or splitting under duress.

It is also designed to protect them from bacteria, which can be a particular problem for athletes who exercise regularly in training shoes or football boots, where the warm, moist environment inside a sweaty sock or shoe is an ideal breeding ground for fungi.

A close-up of Ronaldo’s toenail artwork (X/@Cristiano)

According to Britain’s Royal College of Podiatry (RCPod) there has been a recent small-scale study that showed nail varnish use can protect healthy nails from infection, although there is no professional consensus on it.

Either way, neglecting your feet can have unpleasant consequences — especially in warm climates.

“With over 250,000 sweat glands in your feet, the average person will produce around half a pint of sweat per day in their feet,” says Dr Helen Branthwaite, a spokesperson for the college. “Virtually all fungal toenail infections come from fungal skin infections, commonly known as athlete’s foot, which then spreads to the nail.

“Leaving this skin infection untreated is the biggest risk factor for developing nail fungus.”

Dr Branthwaite believes that despite high-profile sports stars deciding to go for statement nail varnish, and there are specialist varnishes and treatments that advertise themselves as inhibiting the growth of fungus, the best prevention is simply “good foot hygiene”.

Ronaldo, though, seems happy to continue reaching for the little brush to try to be sure. He is a fan of UFC (Ultimate Fighting Championship, an MMA promotion company) where the trend became evident among its professional athletes, and in January this year the father-of-five was a VIP guest at a UFC fight night in Riyadh, Saudi Arabia, where he supported his friend, Russian middleweight Shara Magomedov.

Ronaldo with Saudi government official Turki Alalshikh, left, and UFC CEO Dana White at the UFC night in Riyadh (Chris Unger/Zuffa LLC)

Some fighters don’t limit themselves to just giving their toes a glow-up. Middleweight Israel Adesanya paints his fingernails too, but explains that has more of an aesthetic motivation.

Before UFC 293 in 2023, the Nigerian, nicknamed ‘The Last Stylebender’ told a press conference he wanted to get “drip tips” (a design where the polish is applied in a dripping effect, like melting liquid) on his nails “because it would be disrespectful to knock them (opponents) out with these ugly things. I’ll do my toes as well, in case I kick them in the face.”

As with anything a global icon such as Ronaldo does, the toenail trend could catch on with other footballers.

On Sunday, Atletico Madrid midfielder Marcos Llorente complained about the effect of the heat during their 4-0 defeat by Paris Saint-Germain in both teams’ opening Club World Cup group game at the Rose Bowl in Pasadena, California.

“It’s impossible, terribly hot,” the 30-year-old said. “My toenails were hurting; I couldn’t slow down or speed up. It was unbelievable.”

Before following Ronaldo’s example, though, Dr Branthwaite has more practical advice for Llorente, and others.

“Avoiding walking barefoot in communal areas, such as changing rooms, will also reduce the chances of picking up the infection,” she adds.

So whether it’s flashy drip-tips in the octagon, or black nails on the soccer pitch, a common-sense pair of flip-flops could be equally as important.

They just might not look as fancy.

(Top photo: Stefan Matzke – sampics/Getty Images)