Ofcom is investigating Channel 5's Big Brother after viewers complained over three separate incidents.
More than 1,000 people have voiced concerns to the regulator about the programme and its spin-off show Big Brother's Bit On The Side, presented by Emma Willis.
Ofcom is looking into whether the incidents may have breached the broadcasting code.
Any material which fails to meet "generally accepted standards" must be justified by context according the code.
One incident - in which housemate Conor McIntyre launched a tirade of insults against Deana Uppal - has prompted 1,108 complaints. Many viewers thought it amounted to bullying.
In another, which prompted 114 complaints, contestant Caroline Wharram described a black housemate, Adam Kelly, as a "ridiculous gorilla" with "no sanitation", which some viewers saw as racist.
And in a further incident during an edition of Big Brother's Bit On The Side, former BB housemate Victor Ebuwa used the word "retard" to describe contestants, prompting three complaints.
Last year Big Brother was found to have breached the code after airing offensive language immediately following the 9pm watershed.