The day the Brazilian racing driver Ayrton Senna died in a crash, I was stuck in the toilet of a Manchester swimming pool. The door was open, but my thoughts blocked the way out. It was May 1994. I was 22 and hungry. After swimming a few lengths of the pool, I had lifted myself from the water and headed for the locker rooms. Going down the steps, I had scraped the back of my heel on the sharp edge of the final step. It left a small graze through which blood bulged into a blob that hung from my broken skin. I transferred the drop to my finger and a second swelled to take its place. I pulled a paper towel from above the sink to press to my wet heel. The blood on my finger ran with the water as it dripped down my arm. My eyes followed the blood. And the anxiety, of course, rushed back, ahead even of the memory. My shoulders sagged. My stomach tightened.
Four weeks earlier, I had pricked my finger on a screw that stuck out from a bus shelter's corrugated metal. It was a busy Saturday afternoon and there had been lots of people around. Any one of them, I thought, could easily have injured themselves in the way I had. What if one had been HIV positive? They could have left infected blood on the screw, which then pierced my skin. That would put the virus into my bloodstream. I knew the official line was that transmission was impossible this way – the virus couldn't survive outside the body – but I also knew that, when pressed for long enough, those in the know would weaken the odds to virtually impossible. They couldn't be absolutely sure. In fact, several had admitted to me there was a theoretical risk.
Swimming goggles in one hand and blood-stained paper towel in the other, I ran through the sequence of events at the bus stop once again. I told myself there hadn't been any blood on the screw when I had checked it – or at least I didn't think there had been. Why hadn't I made absolutely sure? I looked at my finger. Wait a minute. What the hell had I done? I had put a paper towel on a fresh cut. There could have been anything on that paper towel. You stupid bastard. I looked at the paper towel, now soggy. There is blood on it. Of course, it's my blood. How can you be sure? Someone with Aids and a bleeding hand could have touched it before me. I threw it into the bin, pulled a second from the dispenser and inspected it. No blood. That helped, a little. No blood on the next one either. But they could have done. I pulled the original paper towel back from the bin. It was bloody. If this is someone else's blood, then why are you picking it up? I quickly washed my hands. I looked in the bin. I couldn't see any other paper towels with blood on them.
Cycling home later, I was pleased with the solution I had found. Of course I couldn't have caught Aids from scratching myself on the screw at the bus stop. That was ridiculous, I could see that now. I had nothing to worry about on that score. I pulled my swimming trunks from my bag and placed them on my bedroom radiator. I rummaged in the wardrobe for my winter gloves and put them on to unfold my swimming towel and carefully retrieve the damp, blood-stained paper towel wrapped inside. I placed it on the radiator next to the trunks. It would take about 10 minutes, I guessed, before it would be dry enough to check properly. Then I reached back into the bag and found the other crumpled paper towels, the ones I had lifted from the bin, and laid them out on my desk. I would check these as well, properly (impossible in the changing rooms), and then surely that would be that. I could put all this behind me. I took off the gloves and turned on the TV. The grand prix was about to start.
Those are my strange thoughts. That is my obsessive-compulsive disorder. I obsess about ways that I could catch Aids. I compulsively check to make sure I haven't caught HIV and I steer my behaviour to make sure I don't catch it in future. I see HIV everywhere. It lurks on toothbrushes and towels, taps and telephones. I wipe cups and bottles, hate sharing drinks, and cover every scrape and graze with multiple plasters. My compulsions can demand that after a scratch from a rusty nail or a piece of glass, I return to wrap it in absorbent paper and check for drops of contaminated blood that may have been there. I have checked train seats for syringes and toilet seats for just about everything. My rational self knows that these fears are ridiculous. I have a PhD in chemical engineering and for most of my career have been a science writer, at one time for the Guardian and now for Nature, the science journal. I know that I can't catch Aids in those situations. But still the thoughts and the anxiety come.
Most people have heard of OCD, but there is much confusion about the condition. It's commonly seen as a behavioural quirk. In fact, OCD is a severe and crippling illness, and one defined as much by the mental torment of recurring strange thoughts as physical actions such as repeated hand-washing. On average, OCD patients can waste up to six hours a day on their obsessions and four hours on their compulsions. A Brazilian man called Marcus had OCD that centred on obsessive thoughts about the shape of his eye sockets, so much so that he was compelled to touch them constantly with his fingers. Marcus prodded himself blind.
It is hard to communicate obsession – severe, clinical obsession, a true monopoly of thought. Here is the best description I have. Consider a computer, and the various windows and separate operations that the machine can run concurrently. As I write this, there is another window open in the background that updates my email, and a separate web browser that tracks football scores. When I choose, I can toggle between these windows, make them bigger or smaller, open and close others as I see fit. That is how the mind usually handles thoughts. It shares conscious concentration between tasks, while the subconscious changes the content of each window, or draws our attention among them. Obsession is a large window that cannot be made to shrink, move or close. Even when other tasks come to the front of the mind, the obsession window is there in the background. It acts as a constant drag on the battery and degrades the performance of other tasks. You can't turn the machine off and on. Whenever you are awake, the window is there. And when you do manage to turn your attention elsewhere, you are aware of doing so. Soon enough, the obsession will reclaim the focus.
OCD is the fourth most common mental disorder after the big three − depression, substance abuse and anxiety. Its impact on quality of life has been judged more severe than diabetes. But people with OCD typically wait a decade or more before they seek help.
The obsessive thoughts of OCD tend to cluster around a limited number of themes. Obsessions of contamination with dirt and disease are the most frequent and feature in about a third of cases. Irrational fears of harm − did I lock the back door? Is the oven switched off? – are the next most common, and affect about a quarter of people with OCD. About one in 10 wrestles with an obsessive need for patterns and symmetry. Rarer, but still significant, are obsessions with the body and physical symptoms, religious and blasphemous thoughts, unwanted sexual thoughts and thoughts of carrying out acts of violence. It's because obsessive thoughts are so often within these taboo and embarrassing subjects that so many people with OCD choose to hide them.
When I found that I could not make my irrational thoughts of HIV go away, I spent a lot of time on the phone to the National Aids Helpline. I would call to tell them how the fears that I had of the virus had spread, and about all of the extra ways my thoughts now told me that I could have caught the disease. It felt good to say those things out loud. Was there, say, a risk when I played football and scraped my knee along the abrasive AstroTurf? Someone else could have done the same after all, and left a smear of infected blood at that exact spot. No, they would respond, no need to worry. The risk was very low. Thanks, I would say as I blew out my cheeks − that's reassured me. But, wait, very low? The risk was very low, so there was a risk? I would dial the number dozens of times a day. Sometimes I would hang up before they answered. I couldn't understand why my mind would circle round, why the sense that everything would be all right was so fleeting. The National Aids Helpline, I quickly worked out, was staffed by about half a dozen people at any one time. I learned their voices, and was encouraged when someone new picked up the phone – surely they would be the one to convince me. After a while, they started to recognise my voice, too. They would tell me that they had already given me an answer and that I needed to accept it. So I invented new scenarios, and even put on different regional accents. Not that it did any good. Reassurance, like offence, is taken, not given. And my mind would not take it.
I know that, somewhere deep down, I can make the choice not to worry about HIV. Someone who is HIV- positive cannot. All I can say is that, to me, HIV has become something to fear, not because of the consequences – perceived or otherwise – but in its own right. I do not fear HIV as it is now understood. It is nothing to do with sexuality, or sex. The fear is a legacy of the uncertainty of the 1980s and those terrifying adverts that told us, "Aids: Don't die of ignorance."
Every night since the age of 19, HIV was the last thing I thought about before I went to sleep. And it was the first thing I thought of every morning. And it was pretty much all I thought of in between. I lost interest in the stuff that had seemed important just a few months previously; music, books and films no longer held my attention. It took me a long time to recognise my problem. I wasn't bothered by crumbs in the bed; I was scared that I would catch a terrible disease, which was very different. So I found it hard to accept that I could be helped.
I eventually went to see a psychiatrist. I was in Leeds, studying for a postgraduate degree, and a psychiatrist came to the university's medical centre once a fortnight. He gave me a red rubber band and told me to wear it on my wrist and snap it against my skin whenever I had an intrusive thought about HIV or Aids. That was treatment for OCD in the mid-1990s. It was called thought-stopping. My band lasted a few hours. The next one survived a day. I went to a budget stationery shop and asked for the biggest bag of rubber bands they had. Thought-stopping, scientists now accept, does not help people with OCD.
The psychiatrist had asked if I wanted to join one of his group sessions for OCD. I didn't: I wasn't keen to hang out with people I thought of as hand-washers. My problem was different, I said, and I doubted anyone with OCD would truly get it. "David," he replied, "I am seeing three other people at this university with OCD and they have the same irrational fear of HIV that you have." I felt a strange sensation; I now realise it was hope. He explained the vicious circle I was trapped inside. The way to stop the ride and get off, he said, was to resist the compulsions. I never smoked, but I imagine that to resist the compulsions of OCD must be like to trying to quit cigarettes. It ultimately comes down to willpower. But what must be resisted in OCD is not a physical craving, but the pull of your own consciousness. In the grip of a compulsive urge, there is nowhere to hide and nothing to reason with.
Some days I had more willpower than others. I learned which situations would prompt the thoughts and the urges, and worked out ways to avoid them. If I was unsure whether someone else had drunk from my glass, I didn't finish it. If an opponent on the AstroTurf football pitch shredded his knee, I would avoid him. In that way, I muddled through. I had good days and I had bad days. I had lots more bad days. It's not that OCD meant I could not function – I did well in exams, I had friends and girlfriends, and I held down some decent jobs. It's just that I was thinking about something else at the time. When I learned that my grandmother had died, when I found out that Princess Diana had been killed and when I saw Pulp Fiction at the cinema, I was thinking about HIV and how I might have caught it. I was thinking about HIV and Aids in the days before I got married – I had met a climate scientist with a sore on his lip at a conference the previous week, and I couldn't be sure that we hadn't mixed up our drinks. OCD stole something from me at that stage of my life: it took away my attention.
My baby daughter was six months old when I noticed the blood on her leg. It was summer 2010 and she wore a pair of shorts and there, above the knee, was a dull smear of red. Strange, there was no obvious cut or graze, and she wasn't in a position to damage herself anyway – crawling was months away, let alone walking. If it was blood, I realised, then it probably wasn't her blood. I was the obvious source of the blood, and sure enough, when I looked carefully, I saw a scratch on the back of one of my fingers. There was a similar smudge on my finger. I must have brushed her leg against my scratched finger as I lifted her. My mind delivered another scenario. It could be someone else's blood. And it could be HIV positive. She could have rubbed it into her eyes.
My baby daughter complained about me lifting her in and out of the swing only on about the 11th time. Yes, the stained part of her leg did seem to touch part of the metal guard as I pulled her out, well, more or less. I couldn't see any blood on the swing, and I couldn't see any blood on the grass underneath, any of the times I looked. I still couldn't see any when I came back with a torch to have another search that evening. I was 38. It was almost 19 years to the day since I discovered that I could not ignore my intrusive thoughts. Before that day with my daughter, I had settled for a life with OCD. From the outside, I probably appeared happy. A little withdrawn, distracted or quiet in some situations, perhaps, but happy. I reversed that decision the day I made my baby daughter an accomplice. I telephoned my local doctor the next morning to make an appointment. It stopped here.
Help for mental health in the UK is patchy, but after I saw my doctor and told him my story, it emerged that we were in the catchment area for a specialist outpatient OCD service based at a mental-health unit at a hospital a few miles away. It was the same hospital where my daughter was born. This time, there would be no elastic bands. And I was determined to make it work. By the time my case worked its way through the health service to reach the specialist OCD unit, my obsessions about HIV had spread to the many different ways I thought I could pass the virus to my daughter, who by now was about eight months old. If I cut myself shaving, or in clumsy attempts at home improvement, I was compelled to wash my hands repeatedly before I touched her.
I was distraught. I had become a hand-washer. My fingers were always chapped and dry. It wasn't only HIV by then. When I discovered that some of the old paint I had enthusiastically stripped and burned from the cupboard doors in our bedroom contained lead, I became convinced I had poisoned her. No matter how many times I cleaned the carpet, if I dropped one of her toys or her milk bottle, I considered it contaminated. More blood tests – this time my wife and I for lead (both normal). My wife drew the line at tests on the baby. I even found a national lead paint hotline to call. On my third enquiry in 24 hours, afraid they would recognise my voice and refer me to the answers they had offered previously, I convinced my wife to call for me. I was concerned not only that I would pass HIV to my daughter, but also that I would act in a way that would make her more likely to develop obsessions and compulsions herself. On that score, I was right to worry: studies since the 1930s have shown that OCD seems to run in families. Relatives of those with OCD are themselves more likely to show symptoms than the general population.
Psychiatrists have thrown dozens of different drugs at OCD over the years, from LSD, lithium and amphetamines to nicotine patches and the horse tranquillizer ketamine. Sertraline hydrochloride is what chemists call a psychotropic medication. I call it a lifeline, a route back to the light from the darkest regions inside my head. I take 200mg every morning. When I swallow the pills, my brain chemistry starts to change and my mind changes with it. Dozens of trials of OCD treatment with SSRIs – sertraline, Prozac and a handful of others – have been carried out with hundreds of people, and a consistent picture has emerged. Patients with obsessions and compulsions who take the drugs are more likely to improve than those who do not. The drugs don't help everybody, but then nothing does.
When I reported to the hospital for my group therapy sessions in the late summer of 2010, if you were to have peered through the window you would have seen a group of half a dozen middle-aged people sitting in a circle and clutching photocopied handouts while a much younger, much better dressed man with dreadlocks and a ready smile moved between them. We could have been learning Spanish. My fellow OCD patients signed up for therapy, as I did, in the full and fair expectation that their involvement would remain confidential, so I'll be vague. Between us, we ticked most of the big OCD boxes – contamination and checking fears, long-standing symptoms, distress and reduced quality of life. Two of the others had obsessions and compulsions linked to Aids. We swapped stories and we tried not to swap irrational fears. And we laughed. We laughed at each other and we laughed at ourselves. We had all long passed the time when we feared our OCD, which had announced itself as a mysterious curse on our lives. It was now a hand on our shoulder, an irritating shadow. We wanted rid of it. But we would probably miss it, too. It was simply a part of us.
We did not talk about our childhoods. The causes of our obsessions were irrelevant to the treatment, because they would all anyway have been different. The symptoms were what mattered, and to find a way to reduce them.
We saw, through wobbly schematic diagrams, how an OCD mind is thought to work. We learned how the compulsions are a short cut that helps relieve anxiety, but only for a short while. We started to identify dysfunctional beliefs and cognitive errors in ourselves. This was cognitive behavioural therapy (CBT), but it didn't feel like the type of treatment we expected. It was mild. We suspected worse was to come. We were right. I was told to smear my daughter in my own blood. Because I feared, probably more than anything else at this point, to touch her with blood on my hands, I was told that the next time I scratched myself or cut myself shaving or drove a nail through my finger I was to seek her out and daub her face, her head, her exposed arms and legs. The anxiety would peak and then, in time, it would come down. Because so many of the obsessions in OCD are bizarre, the exposure therapies used to treat them can appear almost comedic. A 37-year-old engineer whose obsessive disgust at semen allowed him only to have sex in a sterile room he kept for that single purpose was told by his therapists to touch clothes soiled with semen stains and to rub objects with a semen-soaked handkerchief that he was to carry in his pocket. A middle-aged woman with an obsessive fear of animals had to watch as a hamster rummaged through her bedclothes and handbag.
What finally helped me the most was when somebody else offered to take responsibility for my actions. That's pretty cowardly, and I'm not proud to say that it worked, but it did. "I have a good job and I get paid a lot of money," the therapist boasted to us one day. "If I tell you to do something and something bad happens as a result, then you can blame me. I will get sacked. Do you think I would ask you to do something that will get me sacked?" If I had blood on my fingers and touched my daughter and gave her Aids, then it wasn't my fault. He told me to do it. The end result would be the same: I would still have the disease; my daughter would still have the virus. But that didn't seem to matter as much if it was his job to stop it and not mine.
Boom. Psychologists call this moment of clarity the helicopter view. We see the landscape and all it contains in its proper scale. We regain perspective. The six months or so of CBT sessions helped everybody in the group. When we met a few months later, the improvement was still there. I haven't seen the others since, but I hope it still is. Such success is not unusual. Some OCD patients refuse CBT because it sounds too soft. How can talking and thinking, and talking about thinking, dig out deep-rooted obsessions, overgrown with years and sometimes decades of neglect? Others find it too harsh and quit. Some people find a combination of SSRI drugs and CBT helpful; there is some evidence that OCD patients given so-called "smart drugs" – supposed to give a short-term boost to mental ability, and popular with college students – can improve the outcome of CBT. It's common for people who have been through CBT to become evangelists and urge everybody to try it. I'll say only that scientists know it works. They see how the impact can be dramatic and sudden. It worked for me. And no, I never did smear blood on to my daughter.
• This is an edited extract from The Man Who Couldn't Stop: OCD, And The True Story Of A Life Lost In Thought, by David Adam, published this week by Picador at £16.99. To order a copy for £13.59, including UK mainland p&p, call 0330 333 6846 or go to theguardian.com/bookshop.