Two years ago, Dr Teena Clerke received a nasty surprise when she logged online to check her student feedback.

The Sydney academic still remembers every word that flashed up on her screen.

“This woman is so old her views are redundant. She hasn't designed anything since the internet. Why do we need her?”

The anonymous feedback was recorded in an online survey that every student enrolled in her design subject was asked to fill out.

Universities use these surveys to review the quality of teaching and subjects, but staff say they are increasingly being used as tools of abuse.

A recent survey by the National Tertiary Education Union found that 60 per cent of its members had been subjected to disrespectful and abusive comments in student evaluations.

The most common of these comments related to a person’s competency to teach a subject, followed by their gender, cultural background and spoken English, age, personality and political views.

While many universities censor student feedback to eliminate swear words, staff have been told they are “too hot” to teach a subject, chastised for having an accent and one woman was told to “speak up bitch”.

Dr Clerke has received plenty of hurtful feedback over the years, but the comments about her age and credibility hit her hard.

“The next semester I didn't do any lecturing,” she said.

“I didn’t want to do any lecturing because then I’m subjected to criticism because there are not enough pictures, or I didn’t say the right thing or I am too old. It absolutely affected me.”

Dr Clerke, who teaches at the University of NSW and University of Technology Sydney, said undergraduate students were “particularly vicious”.

“There is often a sense of entitlement,” she said. “They pay a lot of money and some feel like they have the right to say whatever they like. They can treat us as the face of the enemy rather than people with feelings.”

The union is calling for a rethink of the surveys, which students are asked to fill out for each subject at the end of semester. They are comprised of scores and written feedback.

The National Tertiary Education Union's national president Jeannie Rea said the abuse was making staff feel distressed, angry and physically ill.

“The last thing we want is for staff to not feel confident,” she said.

Some universities in the United States have abandoned standardised online student surveys due to growing evidence that they are biased against female and minority instructors.

Ms Rea said a better alternative might be to get students to fill out the surveys in class and to then go over the feedback or to discuss the subject with another university staff member.

She is also concerned that the surveys are being used to make decisions on staff performance and promotions when only 30 per cent of students fill them out.

Universities Australia chief executive Catriona Jackson said student feedback should be respectful and constructive, and abuse and disrespect was “never OK”.

“Universities value the feedback provided by student surveys, which help to shape best-practice teaching and learning, and deliver a great education to students,” she said.

She said national student surveys confirmed the vast majority of students were happy with the quality of teaching during their degree.

Dr Clerke now tells her students to email her if they have something personal to say.

She urges them to provide constructive feedback in the surveys and explains they are the only measure of her performance.

“If I am giving a student feedback about their essay, I am not going to say 'you’re not very talented, you’re always late, and I don’t know why you’re bothering with design because you’re so young'.

Imagine if I said that?”