"Everything hurts," the Renaissance legend Michelangelo once declared. Let's be honest: we've all felt that way at one time or another.
Physical pain, emotional pain, aches, soreness, pricks, pangs, twinges, throbs - pain is everywhere.
In fact, a recent review published in the BMJ Open journal, part-funded by The British Pain Society, has found that a staggering number of people in the UK - nearly 28 million, or over two-fifths of the population - is living with pain lasting three months or more, with women more likely to suffer from chronic pain and prevalence increasing with age.
Pain can be disabling and debilitating, but it's also what helps us to survive and protects us from damaging injured parts of our body.
Here's what you need to know about the science of pain...
What happens in our bodies when we feel pain?
When we experience a painful impulse, a lot happens subconsciously before our consciousness settles on what's happened and what the consequence needs to be.
"The nervous system is far more complex than what most people understand," says Dr. Stephen Humble, Consultant in Pain Medicine and Anaesthesia at the London Pain Clinic.
"The nervous system is always on, always monitoring the entire body."
When you cut your finger with a knife, the prick activates nerve endings in the finger, which then activates a pain signal which is carried by the nerve up the arm into the spinal cord. The nerve interacts with another nerve, which then carries the signal up to the brain, triggering multiple parts of the brain, depending on the location and nature of the injury (Is it hot or cold? In your leg or arm?). The brain is able to differentiate between all of these different things.
"The actions that your brain finally concludes we should take is the global pain experience," explains Dr. Austin Leach, Consultant in Pain Medicine at The British Pain Society.
"So what has gone on before in your life has a profound impact on your current pain experiences."
Pain comes in all shapes and sizes
"Acute pain is the pain that almost everyone knows," says Dr. Humble. "It stops you cutting your finger, putting your hand in the fire, standing on broken glass. It protects us."
Chronic pain - which typically lasts at least three months - usually means a dysfunction of the nervous system, when nerve endings start sending signals to the brain even though there's no peripheral injury.
There's also somatic pain, which refers to the skin, and visceral pain, which is in an organ. Dr. Humble cites angina as an interesting example of visceral pain; even though the heart is situated to the left of the chest, pain is experienced as a tightening or crushing in the centre of the chest. Visceral pain can also lead to referred pain, so that an angina sufferer may feel pain going down the left arm, even though there is nothing going on with the left arm.
The nerves supplying that part of the arm and the heart share a common pathway with the spinal cord and spinal pathway, and the nerves in the spine can't tell whether they've been activated by the arm or by the heart, hence why you get pain in both.
How do we know what kind of pain we're feeling?
Why is it that a burn feels different to a muscle tear? You've got specialised nerve endings to thank for that. Your body sends a signal to your brain, alerting it to the type of pain you're in. Think of a fibre optic cable - you have a bundle of nerves all connected to a specialised nerve ending - where one responds to hot temperature, one responds to cold, another nerve ending will respond to pressure, and there are nerves that supply muscles and respond to trauma within the muscles. These different nerve endings are called nociceptors.
How can you be seriously injured and feel no pain?
Victims of shark attacks often speak of how the shark bite didn't hurt, while something emotional like stress can manifest itself as intense physical pain. Say what?
"It all comes back to the way the brain works," says Dr. Humble. He gives the example of having no clothes on when you've stepped out of the shower: you can tell you have no clothes on, and feel yourself putting a shirt on. But after a few minutes, even though you're still wearing the shirt, your brain ignores it.
"Peripheral sensation can be ignored by the brain and can be ignored in fight or flight situations, which can have survival benefit for creatures," he says. When fight or flight kicks in and adrenalin is released, it acts as a natural painkiller and gives you the ability to escape from danger (this is generally short-lived). People who walk on fire or beds of nails share this ability by putting themselves in a trance so that the brain ignores the pain signals.
On the other hand, things like worry, stress, or emotional trauma can magnify an individual's pain because of the strong link between mind and body.
Stress can cause the nervous system to become overactive and can make the brain hypervigilant to stimulation, so that a mild peripheral injury like a vaccination starts to be perceived as a big injury by someone with a needle phobia. If you become anxious and tense and the nervous system becomes overactive, it's primed to send more painful signals.
We all experience pain differently
"Pain is a universal human experience," says Dr. Leach. Yet it's not an identical one.
"What I find fascinating is how two people with different cultural beliefs and backgrounds can be given a painful stimulus and will respond so differently. The painful experience is open to as many different interpretations as there are human beings. You give somebody a strawberry and most people have a similar experience, but you give someone a painful experience and it can range from ecstatic pleasure to agony. Until we know what consciousness is we won’t really understand what pain is," he adds.
Coping with pain
In addition to pain relief medication, there are psychological approaches to managing chronic pain, from meditation and breathing techniques to visual aids.
"Relaxation techniques recognise that by doing a basic physical function you can regain control of your subconscious and redirect subconscious thought processes," explains Dr. Leach.
For example, those reliving a painful past experience and exhibiting uncomfortable symptoms like rapid heart rate, dry mouth and sweating can modify or reduce their pain with meditation techniques to mitigate the unpleasant side effects and often reduce the overall pain experience as well.
"Because the human brain is a learning organ, once you’ve mastered that technique you can reinforce its ability," explains Dr. Leach. Of course, the value of learning these techniques can only be maintained by regular practice and requires a significant amount of self-discipline.
What's next in pain science?
According to Dr. Humble, there are a number of things going on in the field of pain science, from Professor Tony Dickenson's work with molecular mechanisms and developing drugs which specifically target certain areas, to Irene Tracey's use of functional MRI scanning tecnhiques to see where pain is felt in the brain. Professor Praveen Anand is working with Qutenza patches, made from 8% capsaicin (derived from chili peppers) for people with hypersensitive skin from painful scars and shingles. The patches deliberately damage tiny nerve endings under the skin to reduce or eliminate hypersensitivity in selected people.
Another field that's expanding is neuromodulation - this refers to using electricity to modulate the effects of nerves. One example is spinal cord stimulation - you put a medical wire or electrode into the spine itself and then you attach it to a small pulse generator, which can be implanted under the skin and cause tingling in the spine to mask chronic pain. This technique is known as dorsal root ganglion (DRG) stimulation.