Bed posts, furniture legs, uneven flagstone, toys—the world is rife with foot-level obstacles. Far too many for even the coordinated among us to completely avoid. But if our feet and toes are destined to occasionally collide with these hard, inanimate objects, why must even minor stubbings cause major agony?

Yes, your toes seem to be among a select group of body parts that can be injured in a relatively insignificant way and yet still broadcast (at least for a minute or so) that they've been broken or in some other way irreparably damaged. It's as if they've conspired to over-react to every stimulus they encounter. And in a way, that's precisely what they're doing. You should thank them, too.

No Brain, No Pain

To understand why, it's important to first emphasize that pain is a perception; that is to say, it really is all in your head. Whether we're talking about fire, a hammer, or that rock you just plowed your toe into, there's nothing inherently painful in any given stimulus. Instead, it's all about how your brain reads (and reacts to) the information it receives from a given stimulus.

Allan Basbaum, one of the world's leading pain researchers and chair of the UCSF Department of Anatomy, likes to use a beauty analogy. "There's nothing inherently beautiful in something," he says. "And what's beautiful in this culture isn't necessarily beautiful in another, even if it's the same object. Pain is the same way." Your individual experience of pain ends up being a complex mixture of biology, psychology, and other cultural factors. It can be influenced by things like your state of mind, how much attention you pay to it, your memory of previous painful experiences, as well as the intensity of the stimulus and location of the insult.

In other words: Pain is sort of complicated. And we're only now beginning to understand how the brain generates a particular pain experience. Thankfully, acute, or short-lived pain, which is what's going on when you stub your toe, is a bit more straightforward. For most people, a stubbed toe doesn't provoke vast range of pain experiences—it just hurts like hell.

Anatomy of Pain

Sudden and sharp pain serves a very useful purpose: It's a warning, a protective biological signal urging you to stop whatever stupid thing you're (intentionally or unintentionally) doing. Your experience of acute pain will depend mainly on the type and density of nerves in the region you injure, as well as the nature of the stimulus.

Take your pancreas or other viscera. You can actually cut into these parts of your body with little or no pain, explains Basbaum. Stretching them, on the other hand, is absolutely excruciating. That's due to the type of innervation present and the specific stimuli those nerves react to. Similarly, if you took a hammer to an area like your stomach, it would certainly hurt, but it wouldn't produce anywhere near the pain of taking one to your toe or finger. That's because your stomach is both poorly innervated, and, for most people, pretty well protected with layers of tissue.

Your fingers and toes obviously don't enjoy such padding. Both are also packed with nerves, specifically nerve ending receptors called nociceptors that are good at detecting actual or potential tissue damage. When you stub your toe, you're massively stimulating a bunch of these nerve fibers at the same time. Those signals integrate in your spinal cord, which in turn relays that information to your brain. "It's just a really big input," says Basbaum."The brain reads that, and it hurts like hell."

Cortical Homunculus

Speaking of the brain, the type of nerves located in a region of the body and their density also influences the amount of cerebral tissue or cortex devoted to that bodily region. This is nicely represented in what's called the cortical homunculus, a severely distorted "map" of the body within the brain. The hands, lips, tongue, and feet are all much bigger than, say, the hip or trunk. And the part of the brain that receives sensory information from the toes is right next to that part that receives information from the genitals so...yeah, try to avoid stubbing your genitals too.

As far as motor and sensory information is concerned, this all makes sense. Most of us don't use our backs, stomachs, or foreheads to discriminate between things or interact with the world around us. We do use our lips, fingers, and feet, all of which are essential for providing sensory feedback that we rely on to guide our actions. In fact, it's thought that the intense pain of a stubbed toe could even have had an evolutionary purpose. Infections used to kill a lot of people, and our feet, which were frequently in contact with filthy, bacteria-laden areas, were prime targets for these infections via cuts or other open wounds. In theory, anyone who received a lot of sensory information from their toes and feet would be less likely to create those cuts and gashes in the first place, and therefore had a bit of an evolutionary advantage.

I Feel Your (Acute) Pain

Unlike chronic pain, most people have the same levels of acute pain. "It's actually a common misconception that we all have vastly different pain thresholds," says Basbaum. "For instance, pretty much everyone will say 'ouch, it's starting to hurt,' between 43 and 45 degrees Celsius. That just happens to be the threshold of a channel in the pain fiber, the point that channel opens up and starts to conduct," he says.

What is different is people's tolerance of pain, or how much they will put up with before saying 'uncle.' Women, for example, tend to have a lower pain tolerance than men—a surprising finding, Basbaum says, but a true one.1 But that doesn't mean you're completely helpless in the face of pain. While there's no surefire way to completely avoid stubbing your toe, science has confirmed that one of your involuntary reactions actually does help alleviate it: swearing.

Just be sparing with your F-bombs. In a follow-up study the same researchers also found that people who curse more in everyday life don't get the same pain-reducing benefits as those who just swear during painful events.

1UPDATE 8:45 PM ET 04/07/15: This story was updated to reflect the differences in pain tolerance observed in men and women.