But Professor Brett Nixon, Dr Geoffry De Iuliis and a team of researchers are working to advance reproductive medicine for "a healthier future".

They aim to "fill in the knowledge gaps" in the fertility field.

Dr De Iuliis said the children of people with "very poor fertility or older parents have an elevated risk of poor health outcomes".

Professor Nixon said male fertility and sperm quality were "now well recognised predictors of general male health".

"In fact, male infertility is linked to increased risk of testicular cancer, heart disease and diabetes," he said.

"The processes that come together to form fully functional sperm that can achieve pregnancy are very sensitive to environmental stresses."

This made the male reproductive system the "canary in the coal mine of male health".

The number of people seeking help with fertility problems is rising.

"More and more people are seeking assisted reproductive therapies to have families," Dr De Iuliis said.

"We have reached a point now in Australia where one child in every primary school classroom is likely to have been conceived through assisted reproduction."

Historically, infertility was thought to be a female problem.

"It's only in the last couple of decades we now understand that causes originating in men account for 40 to 50 per cent of all human infertility," he said.

He said one in 20 Australian men were "sub-fertile and seeking treatment from IVF clinics".

He said historical stigma may be a reason why this was not widely appreciated.

"At a molecular level we, and others around the world, have shown that a chemical imbalance known as oxidative stress plays a key role in male infertility," he said.

"The potential benefit of antioxidant supplements is an exciting prospect, however more resources are required to continue our advance of this potential therapy."

Science understands some aspects of male infertility, but "there are many things we still don't understand".

"The overall causes are likely to be a complex combination of many aspects of modern living such as diet, environment and social practices such as delaying the start of a family," he said.

"Indeed, as a man ages beyond about 40 years of age, his fertility declines."

Professor Nixon said the age-related decline for men had "a concerning aspect".

"That is, the elevated risk of poorer health in the children of older men," he said.

This includes complex neurological diseases such as "autism spectrum disorders and schizophrenia".

"Data coming from Brussels in 2016 suggests that men conceived through a common IVF technology called ICSI are now showing reduced fertility themselves.

"These studies are still in their early stages, but it will be interesting to follow as more and more men conceived through IVF 20 or 30 years ago look to start their own families."

Dr De Iuliis said it was devastating for people who can't conceive a child.

"Sometimes current IVF technologies can't do anything for them," he said.

"Our laboratory has been working in male infertility for about 20 years and we have been following the decline in male fertility closely."

Professor Nixon said the research team had investigated the effects of "a wide range of environmental contaminants and endocrine-disrupting chemicals on fertility and offspring health, as well as possible ways to alleviate the problems".

"These studies include herbicides (atrazine), plasticisers (bisphenol A), food toxicants and components (acrylamide and polyphenols), cigarette smoke, metals, heat stress and electromagnetic energy from mobile communications."

Previous research has shown that PFAS chemicals can cause male infertility, smaller penis size and lower testosterone.

"This is a common finding for a class of synthetic molecules called 'endocrine disruptors' that find their way into the environment and then our bodies," Dr De Iuliis said.

Asked generally about human exposure to chemicals, Dr De Iuliis said: "We can't escape it. If the potential is there for these chemicals to create long-lasting health effects, which might even be compounded over generations, it's clear we need to escalate research priorities."