As the coronavirus pandemic continues to spread, different opinions on the use of masks have emerged.So, should you wear a mark, or not? The World Health Organisation says only those sick with Covid-19 and those caring for them need to. India's health ministry has advised the same.But up to 25% of people infected with the new coronavirus may not show symptoms, the director of USA's Centres for Disease Control and Prevention ( CDC ) has warned. Other reports have cited data from Iceland showing about 50% of those who tested positive said they were asymptomatic. A research team in Hong Kong has suggested that from 20% to 40% of transmissions in China occurred before symptoms appeared.The high level of symptom-free (asymptomatic) cases would make them spreaders of the virus without realising, making the CDC to “critically review” its guidelines on who should wear a mask . A manual released by the principal scientific adviser to Prime Minister Narendra MOdi has also suggested using masks as a strategy to prevent the spread of Covid-19. Some experts have said that the WHO's position might well have been driven by a global scarcity of masks, forcing even medical workers to make do with homemade masks.China, Taiwan, Japan, South Korea and Thailand — countries with experience with outbreaks of contagious diseases — encourage or enforce wearing masks by all in public. The Czech Republic, Slovakia and Austria are following their example. Masks can stop droplets (from those infected with Covid-19) that are the chief mode of coronavirus's spread.In fact, several studies show that wearing masks might be an effective complement to hand-washing, social-distancing and other measures to mitigate the pandemic. To avoid a shortage of higher-grade protective equipment like N95 masks that can be used by healthcare workers, the White House is expected to announce a policy based on the CDC's guidelines that would urge Americans to wear cloth masks in an effort to prevent coronavirus spread, according to a federal official familiar with the policy.