HIS face is seen on posters all across the island - at coffee shops and restaurants, office buildings and shopping centres.

Yet Jemaah Islamiah fugitive Mas Selamat Kastari, 47, has managed to remain free for almost three weeks.

This begs the question: If he is still here, how can millions of people not spot him when Singapore is 'so small'?

As the search enters Day 19, there are those who believe his physical appearance may have become different from what is seen in the photographs issued by the police, making it harder for passers-by to recognise him.

Mas Selamat's possible hideouts include forested areas. In such places, the shortage of food and the stress of being on the run can cause a person to lose a lot of weight.

For instance, on the American hit reality show Survivor, the contestants shrivel till they are almost unrecognisable, from eating mostly foods foraged on beaches or in jungles.

Minister Mentor Lee Kuan Yew said of Mas Selamat a week ago: 'It was not a prepared escape. Then he's hiding somewhere, either in the jungle eating berries or whatever, or somebody is giving him refuge.'

If the former is the case, the fugitive may well look haggard by now.

Said dietitian and nutritionist Ann Kinsey, from Environmental Nutrition: 'He would have lost a lot of weight on his face, and would be quite drawn-looking.

'His cheek bones would remain high, but his jowls would be withdrawn dramatically, as though he would be sucking in his checks.

'His eyes would appear sunken.'

She added that he would be malnourished, as the body would have started to use up its own store of proteins and fat.

She estimated that he may have lost 5 to 8 per cent of his body weight since the escape.

'He might not look like himself, and may age quickly due to vitamin and mineral deficiencies,' she said.

KL-based Singaporean private investigator Jerry Chang, who has 12years of experience tracking down runaway foreign workers in Malaysian forests, said many of them turn up 'dishevelled and even disoriented'.

The former commando said that even someone trained in survival like Mas Selamat 'can't stay out in the open or even in disused compounds without suffering some changes'.

PROPER REST VITAL

He added: 'In other words, you are not going to end up looking all plump and healthy.'

The rough forest habitat would accelerate the effects of the lack of nutrients.

Psychiatrist Richard Lim said: 'Unless he is sleeping in some comfortable bed, which I doubt is very likely, he will look haggard.

'Proper rest is vital to a human body. You can go without sleep for one or two nights in a row, but the moment you crawl into the third or fourth day, a person can become disorientated.'

At this point, levels of cortisol (a stress hormone) in the body start to rise, which will impair a person's mood and immune system and make him more likely to fall ill.

Said Dr Lim: 'Body temperature starts to fall. The person needs to load up with energy-rich carbohydrates - which Mas Selamat will have difficultydoing.

'He may start losing muscular strength. He may also start suffering hallucinations, which may get progressively worse.

'He may lose sense of time, and may also feel paranoid and insecure and start exhibiting inappropriate, often aggressive social behaviour - which is even more detrimental for Mas Selamat, given the unique situation he is in.'

Psychologically, Mas Selamat may also face tremendous stress as he has to play the waiting game.

Said ex-cop and private investigator Lionel De Souza: 'He would be edgy - living on tenterhooks... Every strange or new sound he hears could mean someone is onto him.'

Added Dr Lim: 'Unless he has managed to make contact with someone, he is likely to get anxious.

'Communication right now is vital as he needs to reach someone who can make the necessary arrangement for him to move out of the public's eye.'

There are other health hazards in the jungle - Mas Selamat could fall victim to a number of diseases, like dengue, or pneumonia from the heavy rain in recent days, and eventually need medical help.

Of course, the heavy rain these few days has also meant an abundance of water, which is one of the keys for survival - perhaps for months, said the experts.

The rain may also have helped the man by washing away his trail.

Then again, it could be that Mas Selamat is nowhere near the forests of Singapore.

Said Mr De Souza: 'We cannot rule out that there are diehard fanatics who could keep him housed.'

Those who harbour or help a fugitive can face life imprisonment, or 15 years' jail and a fine.

Police Assistant Commissioner Wong Hong Kuan said: 'We believe he was unaided, and therefore he does not have access to money, vehicles, or modes of transport.

'That underpins our belief that he is still in the country. That's why we're conducting this very intensive search.'

The director of operations also warned that Mas Selamat, should be regarded as a dangerous man and advised against confronting him.

By now, AC Wong added, Mas Selamat is likely to be anxious, desperate and 'potentially erratic'.

He advised: 'If you see him, do not confront him. Stay calm, walk away, and call the police immediately.'