• If you are healthy, you only need to wear a mask if you are taking care of a person with the suspected 2019-nCoV infection.
• Wear a mask if you are coughing or sneezing.
• Masks are effective only when used in combination with frequent hand-cleaning with alcohol-based hand rub or soap and water.
• If you wear a mask, then you must know how to use it and dispose of it properly.
• Disposable face masks are not effectively protected against airborne viruses or bacteria. However, they can contribute towards reducing the risk of spreading the virus via droplets from sneezing or coughing.

Reference: https://www.who.int/emergencies/diseases/novel-coronavirus-2019/advice-for-public/when-and-how-to-use-masks