Erectile tissue is only found in a few areas of the body, the genitals, breasts and the lining of the nose. This tissue receives extra blood through microscopic passageways, causing the tissue to expand and harden. It is not uncommon when a person has over stimulation of sexuality for the nose lining to swell as well. It is called honeymoon nose, for newlyweds are often engaged in a lot of sexual activities.

The swelling of the nasal erectile tissue, independent of sexual activities, has a distinct, regular pattern of swelling and shrinkage, causing one nostril to be more open than the other at various times through the day. This creates a right/left variation in breath flow. This alternates in a very predictable fashion, every 45 minutes to two hours depending on the individual, and each nostril takes its turn at being predominant in the breathing pattern. It reaches a peak, and then decreases.

This is a natural pattern, but it can be interrupted by emotional disturbance, irregular mealtimes, sleep problems, pollution, infection and other forces that affect the bio-organism. This is why calm emotions, regular routines, and a sensible lifestyle are so important. This left/right breathing pattern affects brain activity, and certain kinds of brain activity are more conducive to particular activities than others.

This rhythm between the nostrils is called "infradian rhythm," a recently coined term for an ancient understanding by yogis who spent great amounts of time in self-observation cataloguing these patterns of the human body. Yogis who focused on this study of the breath were called swara yogis. They also documented the psychological and physiological states that correlated to different nostril dominations in the breath. For instance, the right nostril dominance matched more active, alert states (outer world activities), while the left side dominance promotes quiet, passive and meditative states, (inner world activities). This is very precisely the same as right and left side brain activity. Right nostril breathing is conducive to digestion, and swara yogis were prone to open the right nostril before eating. Before taking fluids and meditation, the swara yogis were inclined to open the left nostril.