Former New York mayor and now Donald Trump's lawyer Rudy Giuliani gave a press conference yesterday, filled with conspiracy theories about election fraud in the US.

Despite that, the most controversial and discussed thing about the event was probably the bizarre cosmetic malfunction Giuliani suffered during his speech, which saw a weird black liquid drip down the side of his face.

While the majority of people assume it was his black hair dye oozing out, others have cast some doubts over the strange liquid.

"He was literally dyeing up there today," comedian Jimmy Kimmel said of the Giuliani.

The black liquid made headlines and was the topic of many jokes and memes all over the globe but no one knows for sure what caused it.

A number of hair stylists questioned by the New York Times said that, while hair dye is the probable culprit, they were not fully convinced.

One of them explained that hair dye does not drip down that way, unless it has just been applied.

"Hair dye doesn't drip like that, unless it's just been applied," David Kholdorov of the Men's Lounge Barbershop told the New York Times.

Another expert suspects the culprit might be mascara, which Giuliani could have used to darken his sideburns.

"Sideburns are more grey than the rest of the head," Mirko Vergani, creative colour director at the Drawing Room in Manhattan, explained. "You can apply mascara to touch the grey side up a bit so it looks more natural."

The Daily Beast also spoke to a cosmetic professional, who pointed to a different possibility: that the dye could be coming from the fake tan on Giuliani's face, rather than his hair.

"He looks like to be wearing a decent amount of fake tan or bronzer or some kind of face makeup," Blackstones colourist and educator Patti O'Gara said.

"So if it's not a shitty hair dye situation, it could be fake tan dripping because it does streak like that when you sweat. It's hard to tell where it's originating from – his hair or his skin."

Another hair colourist told the US-based site Slate that there is a chance it was hair dye, but a very cheap one.

"I would guess that something like this is in the $8 to $15 range," Nicole Wingo of Barber of Hell's Bottom in Washington said.

Whatever the cause, the reality is that a lot of ink has been spilled on Giuliani's leaking dye.