As per who guidelines N95 mask is the right mask to prevent flu. Other mask may not be as effective enough o prevent swine flu. If you are not ill, you do not have to wear a mask. If you are caring for an ill person, you may wear a mask when you are in close contact with him/her and dispose of it immediately after contact, and cleanse your hands thoroughly afterwards. If you are ill and must travel or be around others, cover your mouth and nose. Using a mask correctly in all situations is essential. Incorrect use actually increases the chance of spreading infection.