The nasal cycle in humans, where one nostril is partially congested while the other opens and then switches back and forth, may have several evolutionary advantages. One hypothesis suggests that this cycle helps guard against pathogens by allowing antibody-rich plasma to be squeezed out onto the inner lining of the nose during each cycle, replenishing the nose's defense mechanisms. Additionally, the temperature changes within the nasal passages during the cycle could potentially help ward off upper-respiratory viruses that prefer slightly cooler temperatures just below body temperature. Moreover, giving one half of the nose a rest at a time could be beneficial since noses have to constantly filter and warm air for our lungs 24 hours a day.