As a person without any phobias, I appear to be a relatively rare specimen. (I'm Australian; arachnophobia, while justified, would take up far too much of my time.) The Anxiety and Depression Association of America estimates that up to 19 million Americans, or 8.7 percent of the population have specific phobias, from the common (small spaces, heights) to the rare (people fear everything from clowns to the color yellow). Phobias are technically counted as an anxiety disorder, but the science of how they turn up and what makes them tick is actually more complicated than it seems. You don't feel phobic from germs or snakes because you're weak or peculiar; it seems to come down to a mix of evolution, brain mechanics, and a dose of genetics.
Phobias are widespread and hugely varied. George Washington suffered a serious phobia of being buried alive, while Napoleon allegedly was terrified of cats. But it's only recently that phobias have been deemed worthy of serious scientific attention, and distinguished from plain old fear. It turns out that phobias do significantly different things in the brain than disgust or terror, and that one particular phobia, the phobia of blood, elicits a unique response that may have once saved a caveman's life.
The good news is that phobia cures via therapy appear to be effective and long-lasting. So if a phobia's crippling your life, you can actually get help that will rewire your brain and significantly change your behavior. No more leaping six feet in the air at the sight of a spider for you, thank you very much. In the meantime, here's the how and why of the science of phobias, at least as far as we know.
There's A Lot Of Argument About Why Phobias Happen
For years, scientists thought that phobias appeared because phobic people had a bad experience with the thing they hated: an arachnophobe would have had a traumatic time with a spider as a child, for example. But they now believe this model's a bit too simplistic. It's very hard to track down bad experiences as children, and it seems that many people who suffer from phobias have never had one; the phobia emerges, it appears, from nowhere at all.
There are other theories that have moved in to replace this, though. One is that we're predisposed to be phobic of experiences that might have been dangerous as we evolved as a species: spiders, scorpions, heights, and small spaces may have been "conditioned" into the human brain as highly risky things over the course of human evolution. A 2001 study, in which humans were found to identify and fear images of snakes and spiders far faster than they identified neutral objects like flowers, seems to back this up: something in our neural make-up may be trying to protect us from ancient threats by producing phobias.
And there's also evidence that genetics plays a role. A 2013 study by the Emory School Of Medicine in Atlanta found that if you trained mice to fear the smell of cherry blossom, their kids would fear it too, even if they'd never encountered it before and had no idea what it was. It seems that trauma and fear can be "passed on" down genetic lines, and that an ancestor's horrific experience with a spider or heights may pop up down the generations. But we still don't know if, or how, this applies to humans, so don't go blaming your great-grandmother for your crippling phobia of ants just yet.
How The Phobic Brain Is Different
However phobias turn up, what they do in the brain seems a little clearer. We're now discovering that phobic fear may largely happen in a bit in the brain called the amygdala, which is involved in memory and emotions. It's also what lights up when something dramatic and scary happens, like a gunshot. Studies have shown that you can pick out phobic people from non-phobics by watching their amygdala as they're exposed to fearful stuff (like pictures of spiders): the amygdalae of the phobic people go into hyperdrive and have a strong, quick reaction, while non-phobic people have a slow, more considered reaction. So what's really going on?
Some scientists think that phobic people actually have slightly broken or different amygdalae that can't process fear in a sensible, slow manner. A study in 2013 found that people with arachnophobia have smaller left amygdalae, but they're not sure if that's a consequence of phobias or if it causes them. The American Psychological Association blames phobias on "some kind of dysfunction in the amygdala and related brain areas," but it's not prepared to be more specific than that. People with phobias may have different amygdalae, but we're not sure why or how.
Blaming the amygdala also seems to be borne out by studies on reducing phobias. A 2007 study that tried to help out phobic people through exposure therapy (which is the normal route to defeating phobias, through gradually introducing the phobic thing in increasing amounts) found that the amygdala's activity starts to drop off in treatment. So getting gradually exposed to the phobic thing seems to rewire the amygdala's response and calm it down. And it didn't take long: the scientists saw that there was "significant reduction" in the amygdala's activity after just two weeks of therapy. Good news if you're sick of being terrified of needles or frogs.
Blood Phobias Produce Unique Symptoms
There's one particular phobia that doesn't fit the common type: a phobia of blood. If you're the type of person to faint at the sight of it, this may prove interesting. It turns out that phobias aren't meant to make you faint. Most people, when faced with something they have a phobia about, turn into fight-or-flight machines, ready to flee, panic, scream, and generally be prepared to fight for their lives. That's our standard extreme-fear response. But blood phobias seem to be unique, in that it does the opposite: instead of running away, we drop. Hardly seems helpful.
The Smithsonian Magazine puts forward a few possible theories for why this could be. Both come from ideas about the evolution of man and how a fainting blood phobia may have helped us out of tricky spots. The first is that fainting may have been a way of "playing dead" to help us survive predators if we stumbled across a bloodbath. The second is that a drop in blood pressure (which is behind the fainting and wooziness) may have been a good way to get us to survive serious injury: if we were spurting blood all over the cave, we'd be much more likely to get through it if we had a lie down.
Obviously this isn't very useful nowadays, and is downright embarrassing if, like my 6 foot 3 husband, you tend to crash dramatically if a blood test is required by the doctor. Phobias are, by and large, completely irrational and out of your control, and possible prehistoric hangovers from ancestors with big problems. So no, you're not just being a big baby.