Being the most wanted man in the world can be hell on your complexion. 

Terror mastermind Usama bin Laden lashed out at Americans once again in his most recent video speech, aired Wednesday by the Qatar-based Al-Jazeera satellite news channel, but the ugliness of his words was competing for attention with his drastically changed appearance. 

The past few months have not been kind to Al Qaeda's leader. In the incriminating video, thought to have been filmed in early November, where bin Laden described his surprise and joy at the devastation at the World Trade Center, he appears jolly and plump. 

But in the new video, apparently taped in mid-December, bin Laden looks pale, emaciated and aged, with much more gray in his beard. He also only gestures with his right hand while his left stays motionless at his side — peculiar since the FBI has said he is left-handed. 

But is it just stress from living on the run and hiding in caves, or an ailment, that is wreaking havoc on his previously formidable façade? 

"We're seeing a strained appearance," said Fox News Channel contributor Dr. Isadore Rosenfeld. "It appears he has been under great stress and that may have contributed to an illness ... anyone would be stressed after being subjected to a world-wide manhunt and being bombed and living in caves. It takes a psychological toll." 

While Rosenfeld said that no doctor likes to make a remote diagnosis, there could be hidden medical conditions causing bin Laden's new sunken look. 

In regards to "the apparent immobility of his upper left extremity" Rosenfeld said, "he may have had a stroke — but he doesn't have any facial asymmetry, and his speech is not slurred or impaired [which would indicate a stroke]." 

Bin Laden's seemingly significant weight loss could be from lack of food while in hiding — or a more serious problem. 

"Diseases like an overactive thyroid or cancer can cause weight loss," Rosenfeld said, but added that there's just no way to know for sure. 

The gray beard and pale face could be additional signs of stress or sickness, which Rosenfeld described as an aging phenomenon. 

"They say Marie Antoinette went gray overnight ... stress aggravates everything," he said. Bin Laden may also not be getting much sleep living on the lam and dodging bombs, which can add to the aged look. 

But Rosenfeld points out cosmetic enhancement can play a role as well. 

"He could have been better groomed when he wasn't in hiding," the doctor said. "He could have dyed his beard before and now it has gone back to its natural gray. He could have been wearing make-up before in his appearances." 

Jerrold Post, professor of political psychiatry at George Washington University, found the position of bin Laden's weapon interesting. 

"He's left-handed, but his weapon is placed to his right," Post said. "If he was thinking he might get caught, he would have his weapon near the hand he uses, so this could be a sign that he has been injured or is ill." 

Copious blinking is another mannerism that caught Post's eye. "He's blinking a great deal, which is a significant sign of great duress and stress," Post said. 

Despite the stress and any possible illness, bin Laden continues to stay one step ahead of the world's most motivated manhunters. But the tension and fatigue of evading capture could end up being bin Laden's most dangerous enemy.