A toothbrush subscription company has apologised after attracting heavy criticism for a “foul” marketing campaign aimed at first-year students arriving at universities across the UK.

Brushbox admitted that the inclusion of a beer mat with a suggestive image of a woman’s mouth drooling a white substance resembling semen, with the phrase “spit or swallow” on the reverse, was an error of judgment.

The beer mats were included in promotional boxes distributed to first year undergraduates by a company named Dig-In, which said the material was included in boxes sent to around 45,000 students on campuses.

“We are really sorry if anyone has been offended by the promotional image used in the Dig-In boxes. We now realise it was inappropriate and misguided of us to use this type of image as a way to raise awareness of dental health issues,” Brushbox said.

Brushbox initially tried to defend the image as a “tongue in cheek” attempt to raise awareness about dental health, saying the image was “intended to raise eyebrows”, before issuing a more forthright apology.

Social media users complained that the image was sexist and promoted rape culture. “No one swallows toothpaste. Why didn’t you use a man’s face?” one Twitter user asked the company.

Brushbox sends toothbrushes to customers every two months in return for subscription payments. The service was launched in April, and the company may have thought the controversial marketing campaign would boost its profile.

The Brushbox beer mat has a notch allowing it to be hung on a person’s nose, so that the drooling image covers their mouth.

“Whether you spit or swallow as part of your daily oral regime, place your oral health on autopilot,” the mat reads on the reverse.

The Dig-In boxes have already been promoted through a number of student unions, including Sussex, Keele and Plymouth, as well as through student accommodation providers in Glasgow and other cities.

“Dig-In would like to apologise unreservedly for its part in distributing Brushbox’s promotional material. This insert, distributed in our freshers boxes, does not in any way reflect our high ethical standards and we have put immediate measures in place to ensure this doesn’t happen again,” the company said.

The University of Sussex student union, which distributed the Dig-In boxes on campus, said: “We were very disappointed to find this promotional material in our Dig-In boxes, and we will be reviewing our relationship with the supplier in future.”

Emma Daniel, a Brighton and Hove councillor, told the Brighton Argus: “This is foul – really inappropriate at a place where women are turning up to learn and achieve.”

Dig-In said the Brushbox material would not be included in the remainder of the 400,000 boxes it distributes to new students. Anglia-Ruskin University said it was approached by Brushbox but chose not to include its material in the boxes given to its students.