'Pain is a medical condition that is relatively under-treated, like a poor second cousin,' said a National Cancer Centre pain relief expert, Dr Cynthia Goh.

Doctors tend to view it as a secondary problem to a disease, while patients often accept it as inevitable and do not bring it up, she said.

The extent to which pain is overlooked is unknown, but it can develop into chronic pain, which studies have shown one in five suffers in the United States, Australia and Europe.

Hospitals are now setting up a system to take the amount of pain a patient is in into account and treat him for it.

Since April 1, pain has been monitored at Singapore General Hospital and the cancer centre as a fifth vital sign, in addition to pulse and breathing rates, blood pressure and temperature.

Other public hospitals and specialist centres are expected to start doing so in the next few months.

Patients will be asked to rate, from zero to 10, the amount of pain they feel, and describe it. Those who cannot will be asked to choose from a range of printed facial expressions one that corresponds to what they feel.

Nurses will manage mild pain, but extremely severe cases could be seen by a pain specialist.

Before pain management began, a few medical officers, mostly anaesthetists, trained as pain specialists.

Since the late 1990s, some US hospitals have had to have pain assessment programmes to be accredited.

Routine checks of pain levels, said SGH pain specialist Yeo Sow Nam, would cut down inadequate treatment of pain and alert doctors early to possible complications, such as a wound that has become infected.

Better handling of pain can also prevent its development into chronic pain that is more difficult to treat, he added.

This is increasingly regarded as a disease, as sufferers can become depressed, irritable and anxious, he said.

To raise awareness, SGH will hold a public pain management forum at Block 6, Level 9, on April 24, from 1.30pm to 4pm.