The rhinarium (New Latin, "belonging to the nose") is the moist, naked surface around the nostrils of the nose in most mammals. In actual scientific usage it is typically called a "wet snout" or "wet nose" from its moist and shiny appearance. The groove in the center of it, which reaches the mouth, is called the philtrum.

Anatomically the rhinarium is certainly part of the olfactory system. Whether it evolved from and is part of the main olfactory system, which captured media-borne odors, or the "second nose", the Accessory Olfactory System, which sampled chemicals in fluid solution more directly, has been debated. Ankel-Simons views the rhinarium as "an outward extension of the olfactory ... skin that covers the nasal passages, [which] contains nerve receptors for smell and touch." If that interpretation is true, and the rhinarium extends the olfactory epithelium, the tissue that lines the nasal passages, the rhinarium is part of the main system. In an opposing point of view the philtrum typically traces a path that continues over a notch in the upper lip, through a gap between the first incisors and premaxillae, along a "midline palatal groove" to "a canal that connects with the duct of the vomeronasal organ," part of the accessory system. Where on the one hand the moisture (mucus) may have trapped odiferous molecules in the medium, on the other hand it may be the remnant of a fluid transmission system for molecules of pheromones. The rhinarium is typically crenellated (wrinkled) to increase its sensory area, but, "contra Ankel-Simons," it has no "olfactory receptors" and there is no clear path to the main system.^{[citation needed]}