Mucous membranes form a protective barrier on the surface of all hollow organs that open to the outside of the body. The mucous membranes important to essential oil usage are those that line the respiratory and digestive tracts. Mucous membranes in these areas serve different functions than mucous membranes elsewhere in the body. Some fear that using essential oils aromatically, orally, or internally will damage mucous membranes. That fear is unfounded after a quick examination of how they work and what research has found.