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For many years, I have observed that I breathe only through one nostril.

What can be the reason for this? Is there any cure for this?

  • Consistently the same nostril, or alternating sides over time? – Mark Dec 5 '15 at 4:41
  • yes the sides are alternated over a period of time. but never have i observed that i breathe through both the nostrils... – Aditya Bidwai Dec 5 '15 at 5:41
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    On Biology.SE: Why do I only breathe out of one nostril? – Susan Dec 5 '15 at 9:26
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This question already has a longer answer on our sister site, Biology Stackexchange. In summary, this is normal.

I will quote from the answer of Mike Taylor. The complete answer is a bit longer.

This is natural phenomenon called the nasal cycle. It is discussed in this paper by Telles et al. (1994), among many others. The nostrils are used on an alternating cycle of about 2-3 hours, controlled by the autonomic nervous system. If you notice alternating congestion, that also seems to be coupled to the nasal cycle (Hasegawa and Kern 1977, 1978).

The nasal cycle is a natural ultradian cycle (see here and here. Not only is it present in humans, the nasal cycle has been observed in rats, rabbits, domestic pigs, cats and dogs (see references in Eccles 1996]). Thus, the nasal cycle may at least be a feature of mammals but it may be a feature of other bilateral animals that use nostrils for respiration. In addition, the nasal cycle may be an artifact of the evolution of bilateral symmetry in animals, and how the autonomic nervous system operates between the two sides.

The autonomic nervous system controls the nasal cycle. The autonomic nervous system has two divisions, the sympathetic nervous system and the parasympathetic nervous system. Interestingly, these two divisions show a lateralized ultradian rhythm (Shannahoff-Khalsa 2007). This means that the parasympathetic nervous system dominates one side of the body and the sympathetic nervous system dominates the other side of the body. The two systems later switch dominate sides. This dominance swithcing back and forth between the parasympathetic and sympathetic happens with a regular rhythmic cycle every few hours. As it happens, this switching between sides correlates very well with the nasal cycle (Shannahoff-Khalsa 1991). When the parasympathetic-sympathetic systems switch sides, so do the nostrils. This is also associated with a switch in EEG activity between the two brain hemispheres (Werntz et al. 1983).

Therefore, the nasal cycle may not have a specific function, adaptive or otherwise. Instead, it could result from dominance of the parasympathetic system. Whichever side is dominated by the parasympathetic system will have the primary nostril in use for respiration. However, others have argued that the nasal cycle does provide a function. For example, Eccles (1996) argued that the nasal cycle may function as a respiratory defense mechanism. They found that the rate of cycling increases when nasal infection is present in the nose. They argue that the congestion-decongestion helps generate "plasma exudate" (nasal fluids derived from blood plasma) which may help remove bacteria and viruses.

The nasal cycle is an interesting phenomenon but whether it evolved as an adaptation (such as a mechanism proposed by Eccles et al. (1996) or is simply an artifact of the operation of the autonomic nervous system may never be known for sure.

Original question: Why do I only breathe out of one nostril?

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    (This answer is a community wiki, by the way, so I won't get reputation for copy and pasting someone else's answer) – YviDe Dec 5 '15 at 14:45

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