There is still a long way to go in understanding how best to help victims of child sexual abuse, which can shorten a person's life expectancy and result in the shrinkage of their brain, a royal commission is told.

Psychiatrist Dr Carolyn Quadrio, an Associate Professor at the University of New South Wales, appeared as a witness at a Ballarat hearing of the Royal Commission into Institutional Responses to Child Sex Abuse.

Dr Quadrio told the hearing the sexual abuse of children damaged brain development and, at worst, resulted in shrinkage of the brain and a shortened life expectancy of 10 to 20 years.

"The child feels worthless, betrayed ... they feel dirty, defiled ... they blame themselves," Dr Quadrio said.

"It's extremely damaging for the child's psychological development.

"I think when children are being treated badly, they begin to think 'I'm being treated badly, I'm bad.'"

Dr Quadrio said the grooming of children by predators was "very psychologically abusive, because it's a manipulation of the child's mind."

"They become aware they've been manipulated ... you're dealing with character disturbance."

She told the commission there was "a very strong relationship between abuse and suicide".

Holistic approach needed for abuse victims

Dr Quadrio said the professions of psychiatry and psychology had a long way to go in properly understanding how to work with victims of child abuse.

"I don't think there's enough understanding of the problem of shame. I don't think it's very well understood," Dr Quadrio said.

She said the broadly used method of diagnosis and medication often was not enough for survivors of abuse and they needed "a more holistic approach".

Dr Quadrio told the hearing, "there are a proportion of abused children who go onto abuse themselves".

But they were "by no means the majority" she said.

"It causes dreadful anxiety [in survivors], they feel contaminated.

"They can hold back from their own children because they feel afraid that this thing's going to come out of them in some way."

Dr Quadrio said, in her view, there were no effective screening methods for potential paedophiles infiltrating an organisation.

"Often offenders won't show any abnormalities," she said.

"It's not like there's a test you can do."

She said although "I don't think celibacy drives child abuse," men who were already attracted to children "would feel more comfortable in the priesthood, because the celibacy vow is not going to bother them".

Child abuse survivors finished giving evidence last week.

The hearing continues.