The heart beats wildly, the chest becomes tight and the legs feel like jelly. For people with animal phobias, just a picture of a spider or a dog can be enough to trigger such a reaction.

Phobias can severely limit the lives of those affected and avoidance behavior not only makes the fear persist, it makes it stronger.

"One speaks of a phobia when the fear has become disproportionate. It restricts one's own life and this is associated with considerable suffering," says Heiner Molzen, a behavior therapist in Kiel, Germany.

In principle, one can develop a phobia towards almost any animal. "In my experience, however, animal phobias are most common towards spiders, snakes, and dogs," the therapist says.

Basically, phobias are learned fears. For example, many people who fear dogs have been bitten by them in the past.

However, people who’ve never been attacked by a spider or a snake can also have phobias towards them. This is also due to learning processes.

"When children see how adults react to some animals, they can learn that these animals must be dangerous," Molzen explains.

One experiment examined how babies reacted to photos of spiders and snakes. The infants were unlikely to have had much experience with the animals.

Even so, "we found out that babies have actually shown stress reactions," says Professor Stefanie Hoehl, who heads the developmental psychology department at the University of Vienna.

Another survey found that about half of people have an aversion to spiders and snakes. "That does not mean that a spider or snake phobia is innate," Hoehl says.

However, there seem to be biological factors that mean we develop phobias, or at least an aversion, more quickly to some animals than others.

In the case of a phobia, the decisive factor is not how dangerous something actually is, but how dangerous the amygdala thinks it is.

This primitive part of the brain reflexively links objects and situations to fears without any rational analysis of the actual danger.

"Fear works without us having to think," Molzen says. "In an emergency, it can save our lives if we don't weigh up the risk first, but run straight away."

However, this survival mechanism becomes a problem when there is no real danger.

In order to get the fear under control, the amygdala has to be ignored. That requires establishing new, positive connections in the brain.

Those affected need to either gradually confront the fear trigger step by step or else confront it directly in what is their worst-case scenario.

Each patient can decide for themselves which of those two options to follow, Molzen says.

Together with the therapist, the patient confronts the fear trigger. For example, therapy could start with a picture of the feared animal, followed by a dead animal, and finally the living specimen.

If the patient finds that their fear subsides after 10 to 15 minutes and finally disappears completely, the brain has had a new, positive experience. The old negative experience is essentially "overwritten."

Applied correctly, this form of therapy can work quickly and effectively. "If our brain learns to be afraid, it can also learn not to be afraid," Molzen says.