A facemask or a respirator needs to be used in one of the following conditions only:-

1) For a person who is at increased risk of severe illness from influenza, and if there is a new outbreak of swine flu in the community in a crowded environment, a facemask or a respirator may be considered only if the crowded setting is unavoidable.
2) For a person who is at increased risk of severe illness from influenza, and if he/she is a caregiver to a person with influenza like illness, facemask or respirator is recommended only if being the caregiver is unavoidable. If you are caring for a sick person, you can wear a mask when you are in close contact with the ill person and dispose of it immediately after contact, and clean your hands thoroughly afterwards.
3) For a person who is at increased risk of severe illness from influenza, and if there is exposure in an occupational setting (but not health care) when there is an outbreak of swine flu in the community, use of facemask or respirator may be recommended under certain conditions.
4) For persons who may or may not be at increased risk of severe illness from influenza, but who are exposed in an occupational setting, providing care to persons known or suspected to have swine flu, respirators are recommended.

Using a mask correctly in all situations is essential. Incorrect use actually increases the chance of spreading infection. A facemask or a respirator is not necessary for persons who are not included in the above categories.

There are important differences between facemasks and respirators. Facemasks do not seal tightly to the face and are used to block large droplets from coming into contact with the wearer’s mouth or nose. Most respirators (e.g. N95) are designed to seal tightly to the wearer’s face and filter out very small particles that can be breathed in by the user. For both facemasks and respirators, however, limited data is available on their effectiveness in preventing transmission of H1N1 (or seasonal influenza) in various settings. However, the use of a facemask or respirator is likely to be of most benefit if used as early as possible when exposed to an ill person and when the facemask or respirator is used consistently. Use of N95 respirators or facemasks generally is not recommended for workers in non-healthcare occupational settings for general work activities.

An N95 respirator in addition to blocking splashes, sprays and large droplets is also designed to prevent the wearer from breathing in very small particles that may be in the air. To work as expected, an N95 respirator requires a proper fit to your face. Generally, to check for proper fit, you should put on your respirator and adjust the straps so that the respirator fits tight but comfortably to your face. For information on proper fit, refer to the manufacturer’s instructions.

The 'N95' designation means that when subjected to careful testing, the respirator blocks at least 95% of very small test particles. If properly fitted, the filtration capabilities of N95 respirators exceed those of face masks. However, even a properly fitted N95 respirator does not completely eliminate the risk of illness.

People with chronic respiratory, cardiac, or other medical conditions that make it harder to breathe should check with their healthcare provider before using an N95 respirator because the N95 respirator can require more effort to breathe. Some models have exhalation valves that can make breathing out easier and help reduce heat build-up.

N95 respirators are labeled as "single use", disposable devices. If your respirator is damaged or soiled, or if breathing becomes difficult, you should remove the respirator, discard it properly, and replace it with a new one. To safely discard your N95 respirator, place it in a plastic bag and put it in the trash. Wash your hands after handling the used respirator.