Iceland Moss (Cetraria islandica) has a long history of use in traditional European herbal medicine, particularly in the Nordic countries and parts of Central Europe. It has been used for centuries as a remedy for respiratory tract disorders, such as coughs, bronchitis, and irritation of the throat. The traditional rationale stems from its high mucilage content, which forms a soothing gel-like substance when mixed with water. This mucilage is believed to coat and protect mucous membranes lining the mouth, throat, and airways, thus relieving irritation and dryness.

Several authoritative herbal references, including the European Medicines Agency (EMA) and the German Commission E, recognize Iceland Moss as a demulcent (soothing agent) for oral and pharyngeal irritation and dry cough. The EMA lists it as a traditional herbal medicinal product for the symptomatic treatment of oral or pharyngeal irritation and associated dry cough, based primarily on longstanding use. While there are some laboratory studies suggesting mild antimicrobial and immune-modulating effects of its constituents (such as lichen acids), robust clinical trials validating its efficacy for mucus membrane health are limited.

Therefore, the evidence supporting Iceland Moss for the mucus membranes centers on traditional use and limited pharmacological data, rather than strong modern clinical research.