Why does it hurt when you get a scrape? A neuroscientist explains the science of pain

“How come you feel pain when you fall and get a scrape?” – Tillman, age 9, Asheville, North Carolina

Nobody likes to feel pain, but it’s something every person will experience at some point in their life.

But why is that?

I am a neuroscientist, and my job is to research why and how people feel pain in order to help doctors understand how to treat it better.

What is pain?

To understand why people feel pain, it helps first to understand what pain is. Pain is the unpleasant sensation you feel when your body is experiencing harm, or thinks it is.

Not everyone experiences pain the same way. Pain is a highly personal experience influenced by a variety of biological, psychological and social factors. For example, research has shown differences in the pain experiences of women and men, young and older people, and even across people from different cultures.

It’s important for kids to communicate with a trusted adult if they’re experiencing pain.

Danger signals

A network of nerves similar to wires runs all through the human body, from the tips of your fingers and toes, through your back inside the spinal cord and up to your brain. Specialized pain receptors called nociceptors can be found at the end of the nerves on your skin, muscles, joints and internal organs.

Each nociceptor is designed to activate its nerve if it detects a danger signal. One way scientists classify nociceptors is based on the type of danger signal that activates them.

Mechanical nociceptors respond to physical damage, such as cuts or pressure, while thermal nociceptors react to extreme temperatures. Chemical nociceptors are triggered by chemicals that the body’s own tissues release when they are damaged. These receptors may also be triggered by external irritants, such as the chemical capsaicin, which gives chili peppers their heat. This is why eating spicy food can cause you pain.

Finally, there are the nociceptors that are activated by a combination of various triggers. For example, one of these receptors in your skin could be activated by the poke of a sharp object, the cold of an ice pack, the heat from a mug of cocoa, a chemical burn from household bleach, or a combination of all three kinds of stimulation.

Nerves run from various parts of the body through the spinal cord and up into the brain. Sebastian Kaulitzki/Science Photo Library via Getty Images

How pain travels though the body

When you fall and get a scrape, the mechanical nociceptors in your skin spring into action. As soon as you hit the ground, they activate an electrical signal that travels through the nearby nerves to the spinal cord and up to your brain. Your brain interprets these signals to locate the place in your body that is hurting and determine how intense the pain is.

Your brain knows that a pain signal is an SOS message from your body that something isn’t right. So it activates multiple systems all at once to get you out of danger and help you survive.

Your brain may call on other parts of your nervous system to release chemicals called endorphins that will reduce your pain. It may tell your endocrine system to release hormones that prepare your body to handle the stress of your fall by increasing your heart rate, for example. And it may order your immune system to send special immune cells to the site of your scrape to help manage swelling and heal your skin.

As all of this is happening, your brain takes in information about where you are in the world so that you can respond accordingly. Do you need to move away from something hurting you? Did you fall in the middle of the road and now need to get out of the way of moving cars?

Not only is your brain working to keep you safe in the moments after your fall, it also is looking ahead to how it can prevent this scenario from happening again. The pain signals from your fall activate parts of your brain called the hippocampus and anterior cingulate cortex that process memory and emotions. They will help you remember how bad falling made you feel so that you will learn how to avoid it in the future.

But why do we need to feel pain?

As this example shows, pain is like a warning signal from your body. It helps protect you by telling you when something is wrong so that you can stop doing it and avoid getting hurt more.

In fact, it’s a problem if you can’t feel pain. Some people have a genetic mutation that changes the way their nociceptors function and do not feel pain at all. This can be very dangerous, because they won’t know when they’re hurt.

Ultimately, feeling that scrape and the pain sensation from it helps keep you safe from harm.