Why Do We Sneeze ?

Sneezes are sudden and quick and end in a matter of seconds, and at the wrong time, pretty embarrassing. Yet, we need to entertain such a menace. Why do we sneeze? As you will see, a sneeze helps clear the nose and expel undesirable foreign matter like dust and allergens from the body.

Why do we sneeze ?

Our nasal passage is lined with hairs and sensitive skin. Whenever foreign stuff like dust or smoke enters the nostrils, it nudges the little hairs or irritates the sensitive skin.  The lining releases a group of chemicals that stimulate the trigeminal nerve. The nerve signals reach the “sneezing region” in the medulla area of the brain. The medulla connects the brain to the spinal cord. After the nerve signals pile up to a threshold, a series of neural and muscular actions cause a sneeze.

Sneezes release droplets into the air. Hence, hygiene must be maintained during a sneeze, Credit: Wikimedia/James Gathany

In 2012, researchers at the University of Pennsylvania discovered that sneezing is a nose’s way to ‘reset’ itself. The reset changes the nasal environment and prepares it to trap new particles that may enter the nose.

You may even sneeze if the sun’s a bit too bright. Photic sneeze reflex affects almost a third of the population, which causes the tendency to sneeze when looking at a bright light.

Chronic inflammation or nose stimulation can cause multiple sneezes in a row. Sneezes are the body’s first line of defense, removing allergens, dust, pollen, or other materials that can induce an allergic response.

Steps of a sneeze: The sneeze reflex

There are two phases of sneezing—the nasal or sensory phase and the efferent or respiratory phase. When foreign substances nudge the hairs and the sensitive skin, the trigeminal nerve sends a signal to the medulla oblongata. The medulla responds by activating two neural pathways—parasympathetic and motor pathways.

Parasympathetic activation increases the production of tears and nasal secretions. The motor pathway is the effector (something that causes the effect). It activates the muscles of the throat, diaphragm, and other respiratory muscles.

The motor pathway induces the following muscular actions:

  1. The diaphragm (dome-shaped muscle that helps us inhale and exhale) contracts as we take a deep breath.
  2. The glottis (opening between the vocal cords) shut close.
  3. The respiratory muscles of the chest contract to build up pressure in the lungs.
  4. The glottis opens to let out air, mucus, germs, and other entrapped foreign matter at almost 100 miles an hour. This is the sneeze.
Sneeze reflex arc
Sneeze reflex arc: Flowchart of the nervous and muscular responses in a sneeze

What triggers sneezing

  • Allergens: Any particle that can trigger an excessive immune response can cause allergies. Hay fever is one such response, and sneezing is a part of it.
  • Irritants like pollen, dust, or even bright light can cause sneezing.
  • Viral or bacterial infections can cause sneezing. Sneezing expels the causative pathogen outside the body.

Why do we sneeze multiple times

The reason why we sneeze multiple times is not known; however, people with chronic nasal inflammation may sneeze numerous times. Usually, it depends on whether the sneeze has eliminated the potential foreign particles.

Why do we close our eyes when we sneeze

The reason why we close our eyes while sneezing is not clear. One hypothesis says that this is an evolutionary response of the body to keep the germs and droplets from entering the eyes. Also, our eyes don’t pop out if we sneeze with our eyes open. We will be fine if we can hold our eyelids open mechanically and sneeze.

Hygiene practices with sneezing

Sneezing can release droplets into the air, which may contain bacteria and viruses that can spread respiratory disease if inhaled by another individual. To maintain good hygiene practices while sneezing is of paramount importance. The measures we can take while sneezing, according to the CDC, are as follows:

  • One must cover their mouth and nose when sneezing with a tissue.
  • The used tissue should be appropriately disposed of.
  • One should use their elbow to cover the mouth and nose when sneezing.
  • One must wash their hands for at least 20 seconds to eliminate germs.

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