It is a crippling and mysterious disease that makes everyday life a minefield for some five million Americans - OCD or obsessive compulsive disorder. And one of those people is superstar comedian Howie Mandel. Onstage he makes millions of people laugh, but offstage he can't shake hands with them or touch a doorknob or a glass or even be with his own family at times. Here's David Muir. It's seven o'clock in the morning and Howie Mandel arrives the set of Deal or No Deal. Almost immediately glimpses of the Howie Mandel that he's kept secret for most of his career. Handrails are my enemy. I never go near a handrail. I won't open those things. I would never serve myself. I wouldn't touch this because a lot of people have touched that. This is actually my nightmare. Mandel has obsessive-compulsive disorder, OCD. I love this. Every door should just push out. His obsession with germs, an obsession made famous with his trademark fist bump. And what's the difference between shaking the hand and the fist bump? In my mind this is a petri dish. Otherwise I would spend days, as I have in the past, in the men's room rubbing and scrubbing and scalding. But as we were about to learn Howie Mandel's OCD goes far beyond that fist bump. Off stage it is all-consuming. Look everything's brand new each day. That's normally how a workstation looks. Look at my stuff. It's all brand new not touched. Even Mandel's trademark bald head is this way by choice. This feels so streamlining, so clean, you know, it just feels cleaner. Not even 8:30 in the morning and we've barely scratched the surface. Mandel has written a new book called 'Here's the Deal, Don't Touch Me,' revealing his at times crippling struggle with OCD. It's uncomfortable and it's it's hard and it's somewhat embarrassing. There are many times when I wanted to back out. I'm not somebody who sits down with strangers as I sit here. We go way back. But it's not only you , it's them. Mandel's fans would never know just how deep it goes. Until now the audience had only heard this "Howie Mandel does not shake hands OK? You either knuckle him, you can hug him. You can knuckle him, you just can't shake his hand." Backstage It's a rush to the set. Howie Mandel has been onstage for 30 years now, first making his mark as a manic young comic from Toronto. There would be more than 20 appearances on The Tonight Show Johnny Carson. I've been carrying this for about two months now. It's a lucky rabbi's foot. See a lot of folks would think that's what would set off the panic attack, is sitting next to Johnny Carson, your idol. That's totally different than the fear that OCD injects into my life which is a terror. He would go on to star in the TV drama St. Elsewhere. He was the voice of Gizmo in Gremlins and Bobby in Bobby's World. His daytime talk show. "Here's Howie" He had a short run, years went by, and then just as he considered bowing out of show business altogether the phone call that he first considered an insult. Your wife called this one though right? Yeah my wife said take it, take the deal. Mandel tells us he never could have predicted the show's success. An audience of nearly 20 million viewers an episode, nor did he imagine he'd ever be talking about his mental illness. You dropped the pill. "Yeah". As our camera rolls - "Yeah, it's right here." - He drops the one anxiety pill he brought with him to the set. I don't want you to touch the floor and I won't touch the floor. It's coming off like crazy. Why? I'm not gonna take it. To this day Mandel is in therapy and on medication for the anxiety that comes with his OCD. He won't say which kind because he knows the millions of adults suffering from OCD are also looking for a cure-all. For him, this latest medication came after working with his own doctor and therapist. But you only brought one pill from the hotel? "Yeah." So that means you'll go without it rather than have the one pill that you have? "Right". This is precisely the kind of moment Howie Mandel kept secret for so many years until he let it slip, his battle against OCD on the Howard Stern Show. "You know I've got a germ fetish." What's your big fear? You're gonna get a disease? You're gonna get sick? "Yeah" Did you want to take it back immediately? It was devastating to me, you know, I was incredibly embarrassed and I thought I had humiliated my family. And I thought that this is gonna be the end of my career because people are gonna know that I do have mental health issues. It was like 'What have I just done? What did I do? What did I do? It wasn't funny.' It wasn't funny but it was real and like the 40 million American adults who suffer from anxiety disorders, Mandel's began when he was just a child. He remembers as far back as six years old. They would make fun of me because I couldn't tie my shoes. Oh, I could, but I didn't want to touch it. But I don't want to say I'm afraid to touch it because it's dirty so I didn't. The battle in his mind was constant. I had a like a fight going on inside like I got to wash my hands or I feel filthy or haven't spent enough time in the shower or you know there's something still crawling on me. "There wasn't really a point in living anymore". Mandel is aware of the children we've reported on here after documenting their struggle with OCD for more than a year, their own fears of germs had become debilitating. Like Bridget, afraid of germs from her own family, unable to sit on the same couch as her mother. "No don't". There was Michelle who spent hours in her shower under the scalding water. I pulled her out of the shower and she just sat on the floor, rocking and crying. And there was Rocco who begs his mother to reassure him every day that he won't get sick at school. "Honey, I don't know what you're saying, I don't remember what I said about the day, you'll have a great day. Why do you do this? I said I said a couple things." Mandel sees himself in those children. He said he was an outcast in school, his humor out of bounds. Expelled from high school, he never finished. But he would find a stage, a place for his comedy, and a young woman who found his brand of humor charming. 30 years later she sits beside him as his wife and both remember the title of his first featured act. 'Borderline Psychotic.' When you look back at that marquee? "How did they know?" "Exactly." Do you remember the first time you saw the rubber glove? Yes. I thought he was nuts, but I thought it was hysterical. But even then the rubber gloves were no joke, carrying them for more than his act. And you knew that at the time. We didn't know it was OCD then, but I did know that he took a lot of showers. He had certain rituals that he did but I didn't know what it was. She also didn't know it would get worse. In describing what life is like, Mandel pointed us to the movie 'The Aviator', remembering the portrayal of Howard Hughes. He said that were striking similarities. At the end he ends up naked in a room locked away, urinating into a bottle, and he doesn't want to face the world. And I said, you know, there are times and, I'm not exaggerating, when I'm that close to that. How many times do you think have you been that close to that scene, kind of trapped in a room? There's a couple times moments in a month when it's just hard. When it's just hard to go out, or or you know face anything. A couple of times a month paralyzed by his fears and we wondered how was he able to be a father? How did you raise three children? That was tough. It was tough. The kids when they were crawling on the floor, everything was so hard for him. And there was this. A second house built in the backyard for Mandel to escape the germs of his own family. A solitary place where only Howie Mandel would go. And it's embarrassing, and it's hard especially in front of your child. We have constantly told the kids, daddy's behavior in those moments, is not something to be emulated. Are you able to hug, kiss, touch? Hug, kiss, do everything. It's just for whatever reason, it's the hands. It's the hands. I mean if somebody's sick I'll leave the room. Even the kids? If the kids are sick? Yeah I'm not, well if the kids are sick I'll put on a mask, and if my wife's sick, I won't sleep in the same room. And I don't eat in the same room. I care for them, and I I'll be there, but you know. You'll be there down the hall. Down the hall. You wonder if the kids thought you were a surgeon at one point. Right, I think I was being somewhat trying to be a little bit entertaining. But there aren't many dads who walk around the house with masks on. Yeah ,you know what, the truth of the matter is whoever your dad is or whoever your family is that's your norm. As parents they chronicled the family trips but the whole story was never captured on videos. "Look over here, Jackie." My daughter was a teenager and she crossed her leg and the bottom of her shoe touched his leg, and we were like halfway to the airport and he starts saying, 'You got to take me home,' because that was on the floor and the floors dirty and it touched his pants and think about the germs on his leg.