A nose filter or nasal filter is an air filter

Air filter

A particulate air filter is a device composed of fibrous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. A chemical air filter consists of an absorbent or catalyst for the removal of airborne molecular contaminants such as volatile organic compounds...

 designed to fit inside the human nostrils to prevent the nasal inhalation of allergen

Allergen

An allergen is any substance that can cause an allergy. In technical terms, an allergen is a non-parasitic antigen capable of stimulating a type-I hypersensitivity reaction in atopic individuals....

s, pollutants, and irritants such as dust, smoke, and foul odors. They are generally not intended for protection against toxic or injurious materials such as asbestos

Asbestos

Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. They all have in common their eponymous, asbestiform habit: long, thin fibrous crystals...

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The filters are available in various sizes, and typically have a center clip to facilitate insertion and removal. They are made in a variety of colors. Some designs incorporate an adhesive tab.