Dressing in blackface or brownface is a hurtful, racist and offensive act that mocks, dehumanizes and belittles other cultures while feeding into some of the worst stereotypes of people of colour, community leaders and experts say, reacting to the actions of Liberal Leader Justin Trudeau.

Their comments follow revelations Trudeau wore brownface as part of a costume at an Arabian Nights-themed gala in 2001, and his admission he wore blackface makeup at an event during high school.

"I think that they're both reprehensible in the sense that the idea is that these communities can be replaced," said Tariq Amin-Khan, an associate professor of political science at Ryerson University in Toronto.

People with brown or black skin may feel demonized, "and I think that that's something that should be quite upsetting for anyone," he said.

On Wednesday night in Halifax, Trudeau apologized for dressing up in brownface and a turban for a 2001 gala at the Vancouver private school where he was a teacher. He also admitted that at a talent show when he was in high school, he wore black makeup and sang The Banana Boat Song (Day-O), a Jamaican folk tune made famous by black American singer Harry Belafonte.

The 2001 incident was brought to light Wednesday evening with the publication of an article in Time magazine that showed a picture of Trudeau, with darkened skin and hands, dressed up like the fictional character Aladdin. A second picture later emerged of Trudeau at a talent show at Le collège Jean-de-Brébeuf in Montreal.

Speaking to reporters on his campaign plane Wednesday evening, Trudeau apologized for his actions, saying he now recognizes they were racist.

"I shouldn't have done that, I should have known better but I didn't and I'm deeply sorry," Liberal Leader Justin Trudeau says to reporters about brownface incident. 11:31

'Unacceptable' mythology

Carl Everton James, a professor of eduction at Toronto's York University who researches race and racism, said those kinds of actions are significant because of what brown skin and black skin have come to mean in society.

"Are we doing it because we're saying brown skin or black skin are a noblesse skin colour and therefore we are going to imitate those people?

At one level it shows that Justin Trudeau's understanding about race and racism doesn't seem to have deep roots. - Tariq Amin-Khan, associate professor, Ryerson University

"Or do we see it as a way in which certain kinds of people are not quite like the 'white skin colour' and therefore, we do that," he added. "So it becomes offensive because of what it represents."

In an emotional statement, NDP Leader Jagmeet Singh talked about the racism he has endured in his life, saying that seeing the image of Trudeau in brownface jarred him. He said it's "going to bring up a lot of pain, it's going to bring up a lot of hurt.

"The kids that see this image, the people that see this image, are going to think about all of the times in their life that they were made fun of, that they were hurt, and that they were hit, and they were insulted and they were made to feel less because of who they are."

NDP Leader Jagmeet Singh responds to Time Magazine's article of Liberal Leader Justin Trudeau appearing in brownface and turban at a gala in 2001. 2:28

Although he thanked Trudeau for his apology, Mustafa Farooq, executive director of the National Council of Canadian Muslims, said in a statement that Trudeau's actions are "deeply saddening," and wearing blackface and brownface is "reprehensible."

"[It] hearkens back to a history of racism, slavery and an Orientalist mythology that is unacceptable," he said.

Blackface's dehumanizing history

In the early years of Hollywood, embracing brownface or blackface was common.

"For [Trudeau] not to recognize the deep racism underlying this brownface imagery is quite revealing for me," Amin-Khan said. "At one level it shows that Justin Trudeau's understanding about race and racism doesn't seem to have deep roots."

But Rinaldo Walcott, a professor and director of the Women and Gender Studies Institute at the University of Toronto, said a distinction needs to be made between brownface and blackface.

Trudeau is shown wearing brownface in this 2001 photo published in the yearbook of West Point Grey Academy, a private school in Vancouver where Trudeau was teaching at the time. (Time.com)

"Of course to brown up your face and to dress up as a fictional Arab is troubling and disconcerting," said Walcott, who specializes in studies of black culture.

But blackface has a long enduring deep history used to denigrate and dehumanize black people, he said.

"And that's why it's really important to distinguish that history from the way in which white people have often imitated other people by using some of the same techniques but not with exactly the same kind of intent."

Blacks, for example, were not allowed to appear in theatre, so many white men painted their faces black and recreated some of the worst racist stereotypes, Amin-Khan said.

They would use burnt cork or shoe polish to paint their skin black, leaving wide areas around the mouth that would variously be left uncovered or painted red or white to give the appearance of oversized lips, Philip Howard, assistant professor of integrated studies in education at McGill University in Montreal, wrote in a piece for The Conversation titled The problem with blackface.

"Once in blackface, minstrels would use exaggerated accents, malapropisms, awkward movements and garish attire to further ridicule black people," he wrote.

"I was extremely shocked and disappointed," Conservative Leader Andrew Scheer says after learning about Liberal Leader Justin Trudeau's blackface Wednesday. 0:28

It became a popular form of racist entertainment in the U.S. in the 1820s with the first minstrel shows, Howard wrote. But it also was popular in Canada. Indeed, Quebec musician Calixa Lavallée, composer of the Canadian national anthem, O Canada, travelled as a blackface minstrel.

While the blackface minstrelsy endured into the mid-1900s, performances continued in other forms, and were found on university campuses or during Halloween or other events.

In 2011, for example, a group of white business students at the University de Montreal decide to pay "tribute" to Jamaican sprinter Usain Bolt by painting themselves black. In 2014, students at Brock University in St. Catharines, Ont.,, according to the Toronto Star, "won a campus pub Halloween contest ... after they wore blackface to dress as the Jamaican bobsled team."

As Howard notes, today's blackface wearers may claim they don't believe in the biological inferiority of black people, but wearing the dark makeup "is evidence of their ongoing, racist over-assessment of the significance of skin colour differences. In this way, blackface is dehumanizing.

"The very need to use garish makeup as part of the process of portraying black people reveals an attempt to establish an essential difference between black and white people," he wrote.