Rancic said of the 18-year-old actress' Oscars hairstyle: “I feel like she smells like patchouli oil and weed.”
Coleman posted a response saying that Rancic's remarks were unhelpful, and that she'd worn her hair in that style to "remind people of colour that our hair is good enough."
"There is a fine line between what is funny and disrespectful. Someone said something about my hair at the Oscars that left me in awe," the actress posted on Twitter.
"I was hit with ignorant slurs and pure disrespect. To say that an 18 year old young woman with locs [dreadlocks] must smell of patchouli oil or 'weed' is not only a large stereotype but outrageously offensive. I don't usually feel the need to respond to negative things, but certain remarks cannot go unchecked."
She added: "There is already harsh criticism of African American hair in society without the help of ignorant people who choose to judge others based on the curl of their hair."
Coleman went on to list other high-profile people who have dreadlocks, including Selma director Ava DuVernay and author Terry McMillan. She added that "many other men, women and children of all races" have dreadlocks, and that "none of which smell of marijuana".
Rancic apologised for causing offence, saying that her remark had "nothing to do with race".
The issue of how African-Caribbean hair is perceived in the West has been a touchpoint for high-profile campaigners such as comedian Chris Rock who made the 2009 documentary Good Hair and author Chimamanda Ngozi Adichie, who includes the politics of afro hair in her work.
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