It was the experience of watching people, day after day, whose lives had suddenly changed as the result of a medical diagnosis, that inspired him to become a teacher. He was working in Brisbane, as a clinical scientist in a medical laboratory back in the late 1990s, examining specimens and taking blood from patients.

“I'd often be the first person to know when something was really wrong,” he says.

“And think that affects you in a way, when you're the very first person to look at a result and think, this person's life is going to change. Your story changes, and that's what grief is, pretty much, your future story changing.

Watching that, I wanted to empower people with knowledge. I wanted to give them an idea so that they could interpret what was being told to them by their physician.”

He’s been writing and educating about science and medicine ever since, culminating his latest book, Unwell, an examination on the definition of disease, and how our concept of what constitutes an illness has changed over time.

“We have this idea that there's an authority,” he says.

“The World Health Organisation decides what is and is not a disease. The American Psychiatric Association decides what is and is not a mental health condition. And we ask them, and they say, ‘here's the book’.”

But definitions change, due to both medical breakthroughs and altered societal norms. Gaming disorder (playing too many computer games) is now an official disorder. Being gay is no longer considered a mental deviance. Nostalgia and hysteria were once considered official diseases, while brittle bones used to be seen as just a regular by-product of ageing.

“Often we see it as, an authority makes up their mind on a thing, and they state one way or another. We don't really engage with that, we wait until we're told, and so we treat disease as based on authority that makes up their mind on certain things,” he says.

“Yet they make up their mind because there's a public narrative, there's a story, all the things that have changed are from people standing up and saying, ‘I'm not a disease’.”

Divided into chapters based on the many historical iterations of disease and their modern-day equivalents, the book is both science and history-heavy, but lightened by personal anecdotes and humour. As informative books go, it’s the perfect embodiment of what McRae wanted to do when he walked away from his job as a lab technician.

Although he completed a Bachelor of Applied Science at the Queensland University of Technology, McRae doesn’t consider himself a scientist.

“I call myself a science communicator. A scientist is somebody who actually collects data and interprets it - I don't do that,” he says.

“I eavesdrop on other scientists, and I tell their conversation."

But it was after he had watched too many people - and especially parents - learning that they or their loved ones would die before their time - that he decided to pursue teaching.

He worked for several years as a high school science teacher, an experience he loved.

“I love adolescents. It's the worst time of your life, being a teenager,” he says.

“They're the most predictable of animals in so many ways. Little kids I don't get, they're a bit wild, whereas teens I just love.”

He eventually moved to Canberra to work at Questacon, and then at CSIRO, writing science and developing educational resources. Along the way, he has also discovered that there’s a surprising overlap between health and education, both in the way they’re practised, and the way they’re delivered.

“In both you need to have an individual who diagnoses the progress of another individual student or patient,” he says.

“They both need to have a prognosis, they need to have a treatment. [Health and education] are both under huge pressure as well - time, limited funding - and they're expected to do impossible things to advance somebody to another state, be it a state of health or a state of understanding.”

There’s also the fact that both health and education are considered fundamental human rights, but this concept is constantly muddied by questions of funding and access.

“How much do we pay, and how much does the government pay? How much responsibility does the government have to actually keep their citizens in a state of health or a state of understanding, versus how much do we actually pay for the privilege of knowing more or being healthy?” McRae says.

“There is a lot of overlap between the two systems, and I'm a big fan of diagnostic teaching, so the idea that we give teachers the ability, and I guess the professional respect, to be able to understand their students and decide what direction to go next. But by the same token, we don't really treat teachers will that amount of respect, we don't give them that professional due.”

As it turned out, McRae found himself quickly burnt out by the experience of being a teacher, much as he loved it. The pressures from all sides were simply too great.

“There are so many stakeholders involved in education, so many people pulling each way - parents, principals,” he says.

“There's a feedback loop, I think, with teaching, where on one hand you've got teachers who want to be treated professionally, but you see after a number of years, you fall back to a position that's easier.”

He says a system similar to My Health Record - a way of following a student through their schooling years, and thereby identifying and diagnosing problems - could benefit Australia’s fraught education system.

“The My Health record, for instance, is the idea that you follow an individual through all these different structures and systems and other medical professionals, and they have a history there, you can see where they progress, you can look at these little details and tie them together,” he says.

“Technically we should have the same in education, but we don't. You get to the end of the year, here's your report, move on, and the next year the teacher probably doesn't know anything about that student. They can go back and look through records, but there's no comprehensive way to actually follow through a diagnostic process.

"I taught maths for a number of years, for instance, and that really relies heavily on kids getting something early, and if they miss that, there's no hope.”

It’s not hard to see why McRae stepped away from teaching. But in the meantime, he hasn’t lost his passion for education. With Unwell, he hopes that people will at the very least start having conversations about their own quirks and health issues, so that they can see how much interplay there is between personality and biology.

As part of the book’s narrative, he reveals, for example, on the very first page, that he himself has a disorder called prosopagnosia, that manifests as difficulty in recognising people’s faces. He also talks about his eight-year-old son, Ash, who has Autism Spectrum Disorder. Having a label for these conditions, he says, has been useful for his family. But everyone is different, and that’s the point.

“I'm a big fan of people telling their story, I think everyone needs to have their story out there, because that's what changes things - storytelling,” he says.

“With Unwell, I want people to be telling their story and not be afraid to stand up and say, ‘Here's my experience’, so people [see] that it’s a big blurry thing. Having a label and identity is a good thing, but it's a good thing because it's so diverse, because there are so many stories.”