Nasal sebum, also known as Nose grease/oil, is grease removed from the surface of the human nose. The pores of the lateral creases (where the nose joins the face) of the exterior of the nose create and store more oil and grease than pores elsewhere on the human body, forming a readily available source of small quantities of grease or oil.
Nose grease can be used to minimize scratches in optical surfaces, for example when cleaning photographic negatives. Observatory lore holds that nose grease was used to reduce stray light and reflections in transmissive telescopes before the development of vacuum antireflective coatings. The antireflective properties are due in part to the fact that the nose oil fills small cracks and scratches and forms a smooth, polished surface, and in part to the low index of refraction of the oil, which can reduce surface reflection from transmissive optics that have a high index of refraction. The same effect is sometimes used by numismatic hobbyists to alter the apparent grade of slightly worn coins.
Nose grease has mild antifoaming properties and can be used to break down a high head on freshly poured beer or soft drinks. Wiping nose grease onto one's finger and then touching or stirring the foam causes it to dissipate rapidly.
Nose grease has also been used as a lubricant when playing the banjo. It can lubricate fingers for slides with the fingering hand, or to lubricate picks so they do not 'stick' to the strings when playing.
Great highland bagpipers use it to coat the right pinky finger to play the burl movement more rapidly.