DOCTORS REFER to it as "the silent epidemic" and it accounts for half of all sick days taken from work and billions of euros each year in GP visits and expensive medicines.
Up to a third of us will at some point in our lives suffer chronic pain, according to the statistics.
The International Association for the Study of Pain (IASP) defines it as pain that lasts longer than three months, but other definitions simply characterise it as pain that persists after healing has taken place.
While some sufferers have a recognisable disease process like arthritis or diabetes, others have musculo-skeletal pain, most typically lower backache, often with no discernable cause.
It has also been shown that post- operative pain which is not well managed can develop into chronic pain.
Apart from the pain itself, the condition can seriously impair a sufferer's ability to perform routine tasks, and impact negatively on their work life.
It is also strongly linked to poor health, in particular a higher incidence of obesity.
The psychological stress of persistent pain can make people depressed, and it is often cited as a cause of relationship breakdown.
Unlike acute pain, which serves to warn the body of danger or potential injury, chronic pain has no particular function, explains consultant anaesthetist and pain management specialist Dr Ken Patterson.
"With persistent or ongoing pain, changes occur in the central nervous system and the spinal cord that can be difficult to reverse, and which can go on to form their own disease entity," he says.
So when patients have persistent acute pain, Patterson says, they can go on to develop "chronic pain syndromes".
"One of the things we see with chronic pain is that the nerve or pain pathways continue to fire even after tissue damage has healed."
Patterson admits it is not fully clear why this is happening to some people.
"But there is strong evidence to suggest that the continued assault on the spinal cord of untreated acute pain can lead to a chronic pain state."
Musclo-skeletal injuries often involve neuropathic pain arising from nerve tissue damage, which can be subtle and difficult to discern, as distinct from nociceptive pain which originates from injury or disease outside the nervous system.
Several US studies indicate the brain not only receives pain signals from the spinal cord but also undergoes changes in neural pathways that may permanently strengthen its reactions to those signals.
Experts believe these changes are key to the onset of chronic pain.
Patterson also believes there is a genetic component to chronic pain, citing a number of studies on mice which indicate a "predisposition to chronic pain states" in animals.
The Health Service Executive (HSE)and Health Research Board (HRB) are currently funding a two-year study into chronic pain in Ireland.
The preliminary findings of the Prime study (Prevalence, Impact and Cost of Chronic Pain in Ireland), conducted by a team at NUI Galway, found one in three people reported having chronic pain for an average of seven years, with many reporting significant suffering and reduced quality of life.
Unlike several international studies, which suggest chronic pain affects a higher proportion of women than men, the NUI study found no significant difference between the sexes.
Unsurprisingly, the survey found the lower back was the most common site of pain, followed by the knee, neck and shoulder.
Research co-ordinator at NUI Galway, Dr Brian McGuire, says the most typical cause of pain in the under-65 population was lower back pain, but in over-65s it is knee pain.
"We also found the incidence of pain increases with age, with 28.2 per cent reporting pain in the 18-34 age group, increasing to 50 per cent in those aged 65 and over," he says.
In broad terms, pain is defined by the ISAP as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage".
The definition indicates there is a lot more to pain than just the sensory experience. The emotional state of the person at the time of the pain experience has been shown to affect how they perceive the pain.
While some chronic pain sufferers will be treated with basic analgesic medicines, most pain management physicians believe a more inter- disciplinary approach, taking in occupational therapies and cognitive behavioural therapies (CBT), is more suitable.
Pain management programmes in the US typically involve a team of specialists from psychologists, physiotherapists and pain doctors to rheumatologists and geriatricians.
Limerick-based consultant in pain medicine Dr Brendan Conway believes pain medicine in Ireland, especially outside the main centres, often lacks such a multidisciplinary approach.
"Patients need to have a full understanding of pain, so they can deal with the psychological aspects of pain that we can't deal with through medication," Conway says.
Addressing "negative pain behaviours" such as lack of physical activity or poor sleep patterns, through cognitive behavioural therapy, can significantly improve a patient's quality of life and, in many cases, stop people falling apart, he says.
In oncology, Conway says, psychologists are successfully used to help patients deal with aspects of cancer pain or cancer therapy, but the equivalent in standard pain medicine is often lacking.
The over-reliance on pain medication harbours its own problems, often undermining pain management and leaving patients at risk of addiction.
A recent US study also found the risk of overdose in patients prescribed opioids for chronic pain was strongly associated with the dose that they had been prescribed.
The study, published last month in the Annals of Internal Medicine, assessed the risk of overdose in patients prescribed opioids for chronic non-cancer pain. It linked the risk of fatal and non-fatal opioid overdose to prescription use.