Nasal membranes are tissue inside the nose which serve a number of functions. The bulk of this membrane is made up of a layer of nasal epithelium, with the rear area of the nose having an area covered by olfactory epithelium.
Like other surface membranes, one of the primary functions of the nasal membranes is to protect the underlying tissues and structures. It acts as a barrier to keep viruses, bacteria, and other large particles out, and they help the body retain moisture so that it does not dry out. These membranes also house numerous tiny hairs known as cilia which act to trap particulate matter which enters the nose so that it will not be inhaled.
Another function of the nasal membrane is to act as a sort of air humidifier. When people inhale dry air, they make it more moist. In extremely dry conditions, people may note that their nasal membranes start to dry out, and that this can be very uncomfortable. To keep the nose lubricated, these membranes also secrete mucus. Mucus production can increase when the nose becomes inflamed, potentially generating a runny nose.
The nasal membrane in the back of the nose connect with olfactory nerve endings. Odors dissolve in these areas and hit these nerve endings, allowing people to sense odors. The sense of smell is one of the most primitive human senses, incidentally, which is why people sometimes have such strong memory associations with smells.
Although the nasal membranes act as a block to keep large particles out, they can be highly absorptive if particles are small enough. This is why the nose is sometimes used as a route for drug delivery. The membranes are highly vascularized, meaning that they are connected to a number of blood vessels, and drugs which can be absorbed through these tissues will enter the bloodstream very quickly. Nasal delivery can be accomplished with aerosolizers which generate a spray, or with medications which are smeared inside the nose.
Like other mucus membranes, the nasal membrane tends to heal very rapidly if it is damaged. However, they can be subject to inflammation, swelling and overproducing mucus in response to a real or perceived injury or threat. Nasal inflammation is a chronic problem for some people who may be sensitive to allergens, temperature changes, environmental factors, smells, and other situations encountered by the nose.