Though the avian influenza virus is hosted by birds, some particular subtype might affect other mammals too, including humans. In a direct manner the virus is contacted from infected birds, mostly domestic poultry but sometimes wild birds also can infect hunters, tribal people, etc. In an indirect manner the infection can enter the human system via edibles infected with the virus, polluted water, objects, air, food, etc. by the bodily secretions or excretions of infected birds. The flu virus being airborne, the contamination in the air could be reasonably high, in cases of epidemic or pandemic proportions. Infected people carry the flu virus with them wherever they travel and spread it in air and on objects they touch via their nasal secretions and bodily discharges.

Personal Protective Equipment or PPE as they are called are equipments designed for health professionals to use if they are working in contaminated environments. Nose and mouth respirators or 'Masks' are the ones most widely used. Bird flu masks are very specific pertaining to the fact that the bird flu virus is microscopic and is not easily filtered out from the environment using conventional filters.

These masks are designed on the guidelines given by National Institute for Occupational Safety and Health (NIOSH). Based on filtering efficiency, the filters used in the masks fall under 3 categories, namely Type 95, Type 99 and Type 100. The proportions of microscopic (0.3 micron wide) particles filtered out by these filters are 95%, 99% and 99.7%, respectively. Also the filters are categorized based on filter efficiency degradation and are hence labeled as, N (non-resistant to oil), R (oil resistant) and P (oil proof). Each individual mask is tested in laboratory settings before being approved for sale. But N95 ones are disposable and cannot be cleaned.

The most common ones are N-95 filtering respirators which have been approved by NIOSH (also called as Filtering Facepieces) as being effective drastically cutting down exposure risks to airborne viruses like SARS or Avian Influenza. The usage of masks is recommended to people working in high contamination situations, like health care workers attending to patients, or field workers involved in destroying the infection sources, etc.

Another set of very powerful, protective masks are Powered Air-Purifying Respirators (PAPRs). They are more effective than N-95 masks in offering better protection. These are used by persons who cannot wear N-95 masks, like people with facial hair. This battery operated mask has a face piece with breathing tube and filters.

Even though any mask is not a guarantee against influenza infection, they dramatically cut down the chances of infection from airborne viruses. It remains to be said however, that the capabilities of the masks degrade over time from usage. Aerosols, if present in the working environments, degrade the filters even more. Hence, bird flu masks should not be used with 100% reliance, but only as one of the preventive tool. More so, there are guidelines that need to be adhered to while (re)using such PPE. It is hence clear that the best defense does not lie in any amount of measures taken but rather in the knowledge with which they are implemented