As presenter of the Channel 4’s show Embarrassing Bodies, Christian Jessen has created a persona as the friendly, approachable doctor we’d all be happy to confide in about our deepest insecurities and fears. But as a teenager, he struggled to find anyone with whom to share the angst. “I had quite a tough time of it,” he says. “I don’t blame my parents, I don’t blame my school. I think I made things hard for myself really. I was a bit eccentric and I lived in what I now see was rather a fantasy world. I got through, but it wasn’t always fun.”

Which goes some of the way towards explaining why Jessen has now written a guide to coping with life’s “tricky stuff” for teenagers. “It’s a tough time of life and people often need a bit of help and support,” he says. In his own case, the trickiness of adolescence was partly connected with having been sent away from home in London to boarding school in the Home Counties when he was seven (“It’s definitely too young, but my parents were only trying to do their best for me”) and being an only child. “My dad wanted children and my mum didn’t, but eventually she said OK, we’ll have one – but that’s it,” he says.

“When you’re an only child you tend to be far more comfortable with older people than with your peers, and that makes it hard when you’re sent to boarding school and thrown together with people who are like you, but sometimes difficult to relate to.”

Then there were body image concerns – common enough among teenagers, but particularly pronounced in the young Jessen and, indeed, he admits that his issues persist to this day. “The reason I started going to the gym so often was all about self-doubt and body image – I’m sure a psychologist would put it down to the fact that being gay somehow put my masculinity in question.

“I think I always knew I was gay and I was the child of two liberal, open-minded, academic parents, so I never thought it would be a problem – and it wasn’t,” he says. “But somewhere inside you there’s still worry and doubt about how it’s going to be received.”

Today he thinks the fantasies of his teenage world were part of being gay and having underlying worries about how it would all work out, and he says that at school he did suppress aspects of his character. “But then I went to medical school, to University College London, and suddenly I could see people around me who were clearly gay and I thought, wow. This is all right then, it’s OK to be like this – I don’t have to conform to the heterosexual stereotype.”

Things were easier for him after that in terms of his sexuality, but his discomfort quickly shifted to his chosen career and he wondered if he would fit into the conservative, traditionalist, hierarchical world of medicine. “Being a doctor is all about class, really. It’s all about ‘us’ the doctors and ‘them’ the patients, and from the start I knew I wanted to break all that down,” he says. “There’s this unspoken rule that we are the magic circle, that we mustn’t share our secrets, that we have to keep ourselves above it all and separate.

“But that never worked for me and there were times when I thought, can I really be part of this stuffy, inflexible world? Can I really make it through medical school?”

A few of his fellow students, he remembers, did end up leaving, and he has great respect for them. “Every family wants a doctor in it, parents are so incredibly proud of having a son or daughter who’s a doctor … can you imagine having the balls to get out? All those worries from your mum and dad about what they’re going to tell the neighbours?”

So instead of jacking it in, Jessen, who is 37, stayed put: after his training, he decided to do things his way. He specialised in sexual health – he still runs a sexual health clinic in Harley Street – and he went into television, presenting the Bafta-award-winning Embarrassing Bodies (originally shown as Embarrassing Illnesses) from its launch in 2007. It was at this point, he says, that he realised quite how poisonous the medical world could be to one of their own who decided to opt out. Lots of doctors, he says, quite simply hate him: they hate what he’s doing, they hate what he stands for. They hate the way he chats to the public on Twitter, they hate the way he treats patients as equals and even friends. What’s it all about, he wonders? “When the British Medical Association said it was wrong for doctors to friend patients on Facebook, I think we need to look more deeply at precisely why that is,” he says. “It’s all about putting distance between us, but actually putting distance between us isn’t the thing that’s good for the nation’s health.”

What is good for us, he reckons, is being able to talk about the difficult, the embarrassing and the hidden stuff of life much more easily – and nowhere is this more difficult, or more important, than it is when you’re a teenager. The trickiest part of being a teen, he thinks, is simply how much pressure adolescents are put under: alongside all the physical pressures that are part of puberty and becoming an adult, we’ve created a world in which young people are forced to make life-changing decisions in a very narrow timeframe. “For example, if you want to study medicine you need to decide at 15 because otherwise you might not take the right GCSEs,” he says. “I think we should be more flexible, because it would make life easier for teenagers if we were.”

The Embarrassing Bodies programmes that were given over to teenage issues were, he says, quite simply the best shows the series ever produced: and he knows teens were a big chunk of the viewing audience, because lots and lots of them approached him afterwards to say how much they’d enjoyed it.

Being recognised as a TV presenter has been a bit of a surprise for Jessen and his partner, Rogerio Barreto, who is head waiter at an upmarket restaurant in central London. “It’s life-changing actually, and you have no idea about that until it happens to you. It’s especially hard on the partner of the person in the public eye, because you’re both introduced to people, but all the focus is on the one who’s famous and you want to say, hang on a minute. There are two of us here!”

Would they like to have children? Jessen says he must have inherited his mum’s lack of a parental instinct. “I take after her; I’ve never really wanted children,” he says. “But Rogerio has always hinted he’d like a baby. I guess my mother did it for my father, and maybe one day I’ll do it for Rogerio … but not yet because I’m simply not ready.”

When people ask what he knows about teenagers when he’s not a parent and may never become one, he has a stock answer, of which he’s quite proud.

“I always say, I’ve never had syphilis but I’m pretty good at treating it,” he says. “And the good thing about not having children yourself, when it comes to giving advice and talking about the issues, is that you can be slightly less emotive and a bit more detached about it all.”

Dr Christian’s Guide to Dealing with the Tricky Stuff, by Christian Jessen, is published by Scholastic, £8.99. To order a copy for £7.19, go to bookshop.theguardian.com or call 0330 333 6846