They have become a common sight around Hong Kong in the past week - at hospitals, the airport and even in school playgrounds. But an experienced surgeon said yesterday that many of the masks worn to ward off the threat of pneumonia may turn out to be worse than useless because of their design. Most public hospitals - including the Prince of Wales, the Kwong Wah and Pamela Youde Nethersole Eastern - are handing out paper or cloth surgical masks to patients and visitors as basic protection. The surgeon said most of these disposable masks would not give effective protection. 'How much protection can one get if there is a big gap there and the crucial part of the face is not completely sealed?'' he asked 'Paper surgical masks are flimsy and unreliable, and cannot filter microscopic particles. The material will expand allowing germs to pass through the pores when dampened by the moist produced by the wearer's breath.'' The doctor said non-paper masks were a better option, provided they covered the chin and cheek area tightly. Chinese University microbiology assistant professor Kitty Fung Sau-Chun said masks could not prevent air-borne viruses from entering the respiratory system. 'Masks can only bar virus carried on droplets. For protection against air-borne virus, you have to wear N95 respirators,'' he said.