I awoke close to midnight. It was the middle of August, in 1992, and the windows were open in the room of the Paris hostel where I was staying. The air was warm and still. My chest felt moist with — sweat? I touched the substance with an index finger and pressed it to my thumb. It felt tacky. Blood!

I put on shorts and flip-flops and walked down a flight of stairs to the men’s bathroom. There, I stood in front of a mirror and contemplated the thin, crimson paste that covered my chest. I ran a hand through it like finger paint, searching for the source. Had I scratched a mole? I was starting to feel nauseated. I opened a faucet and splashed water on my neck, shoulders and torso. I patted myself dry with a paper towel, which soon was covered in damp, pink blotches. Pale and sweating, I turned toward the door, grasped the handle and twisted it. Stepping into the hallway, I collapsed.

A specific phobia is an anxiety disorder in which the presence or anticipation of an object, animal or situation provokes intense and irrational fear. Approximately 12.5 percent of American adults will suffer from at least one such phobia at some period in their lives, according to the National Institute of Mental Health. Where I work, one of my colleagues suffers from a phobia of spiders. (She underwent therapy for the condition several years ago, which helped.) Another colleague has a phobia of riding in elevators and, whenever possible, will take the stairs. Yet another is phobic about driving over bridges.

A phobic reaction starts in the brain but instantly affects other parts of your physiology: Heart rate and blood pressure increase as the sympathetic nervous system activates the body’s fight-or-flight response. Some people may sweat, tremble and feel their muscles tense and heart palpitate.

But blood phobia and its next of kin, injury phobia and injection phobia, are different. (The Diagnostic and Statistical Manual of Mental Disorders groups these phobias together as blood-injection-injury phobia, or BII.) Observing blood seep from a wound, flow into a syringe or spatter on the ground, blood phobics initially will respond like other phobics — that is, their heart rate and blood pressure will increase. But then something else will happen: Their heart rate and blood pressure will suddenly drop, causing dizziness, sweatiness, tunnel vision, nausea, fainting or some combination of these symptoms. This is a vasovagal response. The vagus nerve, a component of the parasympathetic nervous system, meanders from the brain stem through the neck, chest and abdomen. It helps to control involuntary “rest and digest” functions, such as lowering heart rate and promoting the secretion of gastric juices. But when it overreacts — in response to hunger, dehydration, standing up quickly, standing too long, intense laughter, sudden fright, severe coughing, pain, vomiting and, of course, the sight of blood, among other triggers — it causes a vasovagal response, which does not generally occur with other phobias.

Blood-injury-injection phobia is a fairly common psychiatric disorder: Studies estimate 3 to 4 percent of the population suffers from it. But why would the sight of blood, or for that matter the sight of being stuck by a hypodermic needle, trigger a physiological response that is so different — practically diametric — to that of other phobias? This is the mystery.

When I woke up, I was lying on my back on the tile floor of the hall outside the bathroom. My body felt heavy and relaxed. An oval ring of faces — fellow students on my study-abroad program — peered down at me. Someone told me my forehead was bleeding; it must have happened when I fell. I didn’t feel like moving. I felt like sleeping on the floor. But I was bustled into a tiny car and driven to a nearby hospital, where I underwent a series of evaluations by a group of medical residents. No big deal, I told them, in amateurish French. I had just eaten poorly that day and was probably dehydrated, too. But the thought of the blood nagged me. I never figured out its source, but I was fairly certain it had played a role in my fainting episode.

A couple of years later, I confirmed my hypothesis after reaching beneath the kitchen sink at my parents’ home in Santa Cruz, Calif., to take out the garbage. I sliced my finger on an unseen lid of a can nestled in the refuse. As blood dripped down my finger, I lay down on the living-room carpet, sweating through my clothes. Had I remained standing, I probably would have fainted. Since then, I have felt nauseated at the sight of blood on several occasions and fainted on another. But what I have always found puzzling about my phobia is this: I’m not consciously afraid of blood; it just makes me feel sick.

So I was intrigued to learn that some researchers have hypothesized that disgust sensitivity may play a role in triggering the vasovagal response in blood phobics. But what little research has been done on the disgust-fainting relationship has yielded mixed results. And one of the most recent studies on the subject, based on a sample of 361 blood donors and published last year in the Journal of Behavior Therapy and Experimental Psychiatry, found no connection between disgust sensitivity and vasovagal symptoms.

Other researchers have suggested that fainting at the sight of blood may be the vestige of tonic immobility — playing dead — that is still observed in many animal species when confronted with specific fears. “This ‘emotional fainting’ could be a physiological activation of a specific evolutionary reflex rather than an acquired cultural phenomenon,” according to a 2001 study in Circulation.

Still others have suggested that blood phobia bestowed an evolutionary advantage: If, while hunting mammoth, you accidentally stabbed your foot with the tip of your spear, low blood pressure may have reduced blood loss and ultimately increased your opportunity for future reproductive activities. Studies show that slightly more than 60 percent of blood phobics’ first-degree relatives also have the phobia, suggesting there may be a genetic component to the disorder. (My brother has become dizzy and sweaty at the sight of blood, though he has never fainted.)

What I have always found puzzling about my phobia is this: I’m not consciously afraid of blood; it just makes me feel sick.

Yet blood phobia presumably would not — at least in modern times — provide much in the way of selective advantage. Emergency medical responders generally can reach you quickly and stanch bleeding. And if you faint, you can sustain a worse injury by falling. The more useful question, it seems, is how to stop from fainting in the first place.

In the early 1980s, a Swedish psychologist named Lars-Göran Öst read a case study, published in the British journal Behavioural Psychotherapy, that intrigued him: The study’s authors, Michael Kozak and George Montgomery of the University of Wisconsin-Madison, had instructed a 21-year-old woman with a history of fainting at the sight of injuries to tense her muscles as a way of coping with such visual stimuli. The tensing increased blood pressure and cerebral blood flow, preventing her from fainting. The authors noted that earlier studies had reported the use of leg exercises and “fantasy-provoked anger” to accomplish the same goal. Yet Kozak and Montgomery wrote that the value of such exertion “probably lies in its allowing prolonged exposure to the eliciting stimulus, thus allowing adaptive relearning to occur.” In other words, they viewed the technique as a tool for assisting treatment rather than the main engine of treatment.

Photo by Erin Kunkel

Öst and a colleague, Ulf Sterner, conducted a study in which blood phobics tensed their muscles in response to blood stimuli. The results, published in the paper “Applied Tension: A Specific Behavioral Method for Treatment of Blood Phobia,” showed that the relatively short treatment sequence — five one-hour sessions — led to marked improvement. First, participants practiced tensing muscles in their arms, torso and legs for 10 to 15 seconds, until they began to feel their faces flush. Then they did this while observing slides and videos of blood and, later, while observing blood withdrawal. Finally, they used the applied tension technique while watching live thoracic surgery. At the end of the treatment sequence, the participants watched a 30-minute video of a thoracic operation. Every one was able to watch the entire film without fainting or, for that matter, experiencing any vasovagal reaction, the study says.

In 1991, Öst and some colleagues compared various techniques for treating blood phobia: applied tension, in which participants tensed while exposed to blood stimuli; tension only; and exposure only. The results were dramatic: 90 percent of the applied-tension group and 80 percent of the tension-only group showed improvement, compared with just 40 percent of the exposure group. These findings indicated that the coping skill — tension — was the crucial component, the researchers wrote.

I called Öst at his home in Uppsala, Sweden. He is on the faculty of Stockholm University. “I was surprised at how effective applied tension was,” he says. “Having worked earlier with other coping techniques, we supposed the patient would use the technique post-treatment, when they were watching the thoracic surgery film. We were astonished when more than half the patients in the applied-tension group said they hadn’t used it while watching the film. When we asked why, they said they hadn’t needed to. They said, ‘If I had the symptoms, I knew I had an effective technique I could use.’”

He continues: “In some ways, it seems they got a boost of confidence by learning this technique and were no longer afraid that they would suffer the symptoms yet be unable to do anything about it.”

Craig Barr Taylor, a professor of psychiatry at Stanford’s medical school, has treated many phobics, including my colleague with the spider phobia. He is the director of the Stanford Hospital & Clinics anxiety disorders clinic, which is where I met him, in his office, last fall. He has a ring of white hair and a white mustache, and he looks relaxed and vaguely amused. I had arranged the meeting with him to undergo a session of applied-tension therapy. The blood-injection-injury phobics whom he had treated before were mainly patients who needed to give themselves shots, such as diabetics. “But I also really do see a public health benefit to this therapy,” Taylor says. “Blood donation is important for society.”

“Squeeze your feet and your legs, your hands and your shoulders and chest until your face feels flushed. OK — Breathe.”

Treatment for most phobias, he explains, is done by gradually exposing people to the objects of their fears. For example, arachnophobes will first sit in a room with a plastic spider on the table. Then a dead daddy long-legs in a jar will be placed on the table. Then a live daddy long-legs in a jar. Then the patient will touch the jar with a ruler. And so on until the patient can actually hold a spider in his or her hand. Often the patient will perform deep breathing and other relaxation techniques during the exposure therapy. “When the brain looks at something it fears under conditions of perceived safety, it will habituate to that fear,” Taylor says. “It’s one of the most profound and important parts of our biology.”

In applied-tension therapy, exposure is combined with the coping mechanism of tensing muscles. I practice the technique, and Taylor coaches me: “Squeeze your feet and your legs, your hands and your shoulders and chest until your face feels flushed,” he says. “OK — breathe. Remember to breathe. Perfect. Now relax.” We practice this several more times. He has to keep reminding me to breathe normally, which I find difficult to do while tightening my muscles at the same time. Soon I feel the itchy sensation of sweat forming at the top of my forehead.

Next, Taylor shows me an image, on his computer, of a dark-orange dot. It does not look like blood, but I look at it while tensing my muscles for 10 seconds. No problem. “We’ll just see your reactions to these and how far you can go,” Taylor says.

He tells me to close my eyes as he puts a new image on the screen of the computer. It is a red dot. I tense my muscles. No problem. And so it goes, until I am looking at blood dripping off the cuticle of a nail. Still, no problem. “I love treating phobics,” Taylor says, grinning. “It’s so wonderful to see people do these exercises and get better quickly. It’s so effective.”

The Stanford Blood Center on Hillview Avenue, near Foothill Expressway in Palo Alto, is housed in a modern concrete-and-glass building. I drive there a few days after practicing my applied-tension technique with Taylor. I meet training supervisor Mary Hayes, RN, who has worked at the center for 14 years. She teaches nurses and medical assistants how to withdraw blood for donation.

The blood center, which also has locations in Menlo Park and Mountain View, supplies blood and blood components to seven hospitals in the region, helping an estimated 100,000 patients annually. To meet that need, it must collect 200 pints of blood a day.

“A lot of donors, when they are sitting in that chair, they’ll look at you and they’ll say, ‘You know what? I really don’t like needles,’” Hayes says. “And I’ll look at them and I’ll say, ‘Honey, you’re in the wrong spot.’”

Some experience a vasovagal response simply as a result of parting with a pint of blood, which lowers blood pressure. “You’ll look at a donor and think, ‘He wasn’t that color a few seconds ago,’” she says.

Still, only a small number of blood donors actually suffer a vasovagal response. In such cases, the center’s staff generally will tip back the donors’ chairs to get their feet in the air and encourage blood flow to the head. “Usually, they recover within minutes,” Hayes says. “It’s very, very quick.”

Drinking 16 ounces of water half an hour before donating blood can help prevent the vasovagal response; water increases sympathetic-nervous-system activation and blood pressure, Hayes says. She also says coughing, which increases cerebral blood flow, is a good coping mechanism.

I watch a globule of blood begin to form and slide down my finger. I tense my muscles and concentrate on the blood.

I walk on to the floor of the blood-drawing area and sit down in a chair next to a middle-aged man. He smiles at me. I ask whether he would mind if I watch him donate blood, and I explain why. Not at all, he says. A few minutes later a needle is inserted into his arm and blood begins to flow into a slim tube. I begin tensing my feet, legs, arms and shoulders. I feel awkward staring at someone while turning red in the face, but I soldier on. I soon realize, after doing the exercise twice for about 10 seconds each time, that I’m not going to feel sick or faint. I relax my muscles and continue gazing at the blood.

Later, I ask Öst, the Swedish psychologist, whether he thinks treating blood phobia was any easier than treating other kinds of phobias. “I don’t think that it is possible to conclude that blood-injection-injury phobics, in general, are easier to treat than other kinds of specific phobics,” he says.

Was I cured? I wasn’t certain. I decide to give myself one final test.

I visit Taylor again, and this time I bring a box of lancets with me. Meeting in his office, I swab my middle finger with some alcohol. Taylor pulls the cap off the end of a lancet.

“Are you ready?” he asks.

“Yes,” I say.

It is virtually painless; it feels more like an intense itch than the prick of a needle. I watch a globule of blood form and slide down my finger. I tense my muscles and concentrate on the blood. After about 10 seconds, I relax. I am fine.

“You are amazing,” Taylor tells me. “Do you know what you just did? I’m so proud of you. If you can do that, you can do anything.”

I wrap a bandage around my finger, thank him and walk out of the office. What surprises me most is the realization I have overcome a physiological response that, until recently, I was pretty sure was out of my control. It feels akin to suddenly discovering you can move an object with your mind. In the process, I tricked my brain into calmly entertaining the sight of blood.

The photo that accompanies this article was taken a couple of months after my last meeting with Taylor. Though I knew the plan for the photo was for me to hold a vial of blood, I didn’t bother using applied tension before or during the shoot. I felt strangely nonchalant about the possibility of fainting or feeling sick, my confidence bolstered by all I had done before.

E-mail John Sanford