It can be sharp or dull; it can last for a few seconds or for a lifetime. If it's bad it can make you vomit, and we spend millions a year trying to make it go away. Pain affects us all at some point. In the West, the traditional treatment is a bottle of pills, in the form of analgesics such as ibuprofen or paracetamol. But painkillers can have unpleasant side effects, including addiction.
Is there an alternative to drugs? Two London doctors, Chris and Alexander ("Xand") van Tulleken, who are also identical twins, set out to investigate if we can learn anything about pain relief from other cultures.
Both twins, 29, studied medicine at Oxford University and trained at the city's Radcliffe Camera Hospital. They believe that Western medicine is missing a trick, so they teamed up with Channel 4 to do a series about alternatives to Western medicine, called Medicine Men; the second episode in the series examines pain.
"We heard about a Hindu festival in Malaysia, where people pierce themselves and claim to feel no pain," says Xand. "We wanted to learn whether there are ways of controlling extreme pain just with your mind."
So they decided to perform an experiment: they'd both get pierced at the festival, but one of them would prepare for it and the other wouldn't. Because Chris and Xand are identical twins, they are ideal subjects: one can be a control, the other a variable.
"I prepared according to the Hindu priests," says Xand, "while Chris just rolled up on the day. I also spent a lot of time talking to people who had done it before. The man who was going to pierce me said, 'Don't worry, I'll put you in a trance', and I genuinely thought he would just do something to me on the day."
Chris was more sceptical. "I turned up with a hangover and I'd been doing all the things you're not supposed to. I've never been able to be hypnotised, and I was certain that it was going to hurt. Wwe were dressed up in sort of Aladdin trousers, covered in beads and had turmeric in our hair. We felt pretty stupid until we got to the area where people were being pierced and it was quite a sombre atmosphere.
"Xand was pierced before me and it was quite a violent process. The spikes are sharp, but not that sharp, so they had to force them through. I saw Xand's arms come up from his sides to stop the guy from piercing his tongue, but someone held his arms back."
After an hour, the spikes were removed. Chris, who had done no preparation for the event, recovered quickly, whereas Xand didn't find it so easy.
"I really felt like I'd been assaulted," he says. "I was really quite upset and choked up at the end – and was also in a lot of pain."
Chris says: "The others were simply acting like it was Christmas," says Chris. "It wasn't bullshit and it wasn't just painful devotion – they were really entering some kind of trance state. We came away pretty convinced that it is a phenomenon."
Britons spend £300m a year on over-the-counter pain relief, and 10 million of us suffer from chronic pain. The most common cause is arthritis, followed by back pain. "All pain is in the brain," says Xand. "The pain pathways to the brain have been so reinforced that even if the thing that's making it hurt is taken away, the brain still feels the pain."
It is also subjective, adds Chris. "I have seen patients with sprained ankles vomiting and white as a sheet: they can't cope at all. But then someone will come in having lost all the skin off one finger and be quite relaxed."
Another dimension is placebos. "The fact is that they work – and they work best when both the patient and the doctor believe that they will work," says Chris.
The modern understanding of the placebo effect is in part down to Dr Harry Beecher, an Army medic. Dr Beecher ran out of morphine while treating casualties in Italy. He gave them saline solution instead, telling them that it was morphine – and found that in 40 per cent of cases their pain was relieved anyway.
Doctors are increasingly prescribing cognitive behavioural therapy (CBT) for chronic pain, which can potentially "break" pain pathways to the brain. Dr Joan Hester, a consultant at King's College Hospital in London and president of the British Pain Society, believes attitudes are changing. "The use of painkillers long-term certainly has problems," she says. "They can work if used properly, but there is evidence that taking painkillers for headaches can make them worse. Chronic pain is made worse by the anxieties about the pain itself, which can be treated simply by allaying the patient's fears. CBT can be very effective, but there is a shortage of practising psychologists – and pain can be very disabling if it is left untreated."
There has also been a resurgence in the number of surgeries being performed under hypnosis, rather than general anaesthetic. Hypnosis is thought to reduce both blood loss during the operation and recovery time. In 2006, a hernia operation was successfully performed on a hypnotised patient live on the More4 television channel.
"In a search to be so rational and scientific, Western science has cut itself off completely from a form of healing that falls under the umbrella term of the placebo effect," says Xand. "After what we saw in making the programme, we feel that's a mistake."
Medicine Men starts on Channel 4 on 22 January at 9pm
What pain is, and how to stop it
* When part of the body is injured, nerve endings transmit pain signals to the brain via the spinal cord
* However, the degree to which the pain is felt may depend on other factors such as degree of fear and the general health of the injured person. Hence, dental pain, for example, may be felt more severely than the treatment causing it would suggest
* Most over-the-counter painkillers work by blocking the body's production of prostaglandins, one of the chemicals that produce the sensation of pain. Narcotic painkillers such as morphine work by blocking the chemical messengers that carry the pain signal to the brain
* Pain is exacerbated by tension, so many relaxation techniques can ease it. No one knows for sure why it works, but acupuncture is particularly helpful for musculo-skeletal pain. It is available on the NHS, but access is limited and many doctors dispute its effectiveness.
* The most painful diseases are thought to be necrotising fasciitis (flesh-eating disease), trigeminal neuralgia (a nervous disorder causing pain in the nose, eyes, lips and jaws – labelled the "suicide disease"), gout, kidney stones, gall stones and cluster headaches.