How Sneezing Works
In this episode of Stuff You Should Know, the hosts explore the biology and mechanics behind one of the body's most powerful reflexes: sneezing. They explain how specialized cells in our nasal passages detect irritants and trigger a coordinated response from multiple muscle groups, resulting in projectile speeds of up to 100 mph and droplets that can travel up to 30 feet.
The discussion covers common causes like allergies and colds, as well as unusual triggers such as bright light exposure and overeating. The hosts also examine how different cultures have interpreted sneezing throughout history, from ancient Persian beliefs about demon expulsion to the origins of saying "God bless you" during the Black Plague, and how these cultural practices compare to modern public health guidance.
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1-Page Summary
The Biology and Mechanics Of Sneezing
When irritants enter our nasal passages, specialized cells detect them and signal the brain's "sneeze center" in the lateral medulla. This triggers a powerful reflex that coordinates multiple muscle groups to forcefully expel air. According to Josh Clark, these sneezes can reach speeds of up to 100 mph, projecting droplets as far as 25-30 feet. These droplets can remain suspended in the air for several minutes as a fine mist.
Causes and Triggers Of Sneezing
The most common cause of sneezing is rhinitis, which can be triggered by allergies, colds, sinus infections, and environmental irritants. Josh Clark reveals he experiences photic sneezing, a genetic trait affecting 23-25% of people who sneeze in response to bright light. The hosts also discuss rarer conditions like "snatiation," where people sneeze after overeating, and unusual triggers like sexual arousal or orgasm.
Cultural and Historical Beliefs and Practices Around Sneezing
Throughout history, different cultures have attached various meanings to sneezing. Ancient Persians believed sneezing expelled demons, while the practice of saying "God bless you" originated during the Middle Ages' Black Plague. In China and Japan, the number of consecutive sneezes is believed to indicate whether someone is speaking well or ill of you. Chuck Bryant and Josh Clark note that modern public health guidance has largely replaced these traditional beliefs, emphasizing the importance of covering one's mouth and nose when sneezing to prevent the spread of illness.
1-Page Summary
Additional Materials
Actionables
- You can create a personalized sneeze kit to carry with you, including tissues, hand sanitizer, and a small informational card about sneeze etiquette to share with others. This kit ensures you're prepared to cover your mouth and nose during a sneeze, minimizing the spread of droplets, and it serves as a conversation starter to educate others on the importance of sneeze hygiene.
- Develop a habit of tracking your sneezing patterns in a journal or app to identify potential triggers and correlations with your activities or environment. By noting when you sneeze, the intensity, and possible causes, you can better manage your exposure to irritants or discuss patterns with a healthcare provider if you notice unusual triggers or an increase in sneezing frequency.
- Experiment with adjusting lighting in your environment if you experience photic sneezing, using dimmer switches or sunglasses to manage light exposure. This can help reduce the frequency of sneezes triggered by bright lights, making you more comfortable in various settings, especially if you find yourself sneezing frequently when stepping outside on sunny days or when encountering bright artificial lights.
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The Biology and Mechanics Of Sneezing
Sneezing is a powerful reflex designed to expel irritants from the nasal passages, involving a complex system of detection and a coordinated muscle response.
Sneezing: A Reflex From Nasal Irritation
When external particles enter the nasal passages, they can cause irritation. The nasal passages are designed with narrowness to induce turbulence, helping to move air toward the sides where specialized cells can detect irritants.
Nasal Passages Detect Particles and Signal the "Sneeze Center" in the Brain
The specialized cells, such as mast cells and irianophils, activate when they encounter irritating particles. They release histamines and send a chemical message to the sneeze center of the brain, located in the lateral medulla. The brain's sneeze center then coordinates a rapid response to expel these irritants. Evidence for the location of the "sneeze center" include the case of a fisherman who, after developing a lesion in his lateral medulla, lost the ability to sneeze.
Brain Coordinates Rapid Air Expulsion to Remove Irritant
The sneeze center of the brain commands a complex, involuntary reflex that happens in about a second and involves many muscle groups to eject the irritant from the nose. This action is not consciously controlled and is a result of a coordinated sequence of events triggered by the brain upon detecting nasal irritation.
Sneezing Involves Coordinated Muscle Contractions
A sneeze requires the participation of multiple muscles to generate the necessary force.
Diaphragm, Chest, and Abdominal Muscles Expel Air Forcefully
Chuck Bryant explains that when you have back problems, a sneeze can really tweak it, which indicates how a sneeze involves the abdomen, chest, and diaphragm. Josh Clark adds that the diaphragm pushes the air out violently during a sneeze through both the mouth and nose.
Vocal Cords Clamp to Build Pressure Before Releasing Air
The vocal cords first clamp shut, as explained by Chuck Bryant, to build pressure within the chest just before the powerful expulsion of air occurs in a sneeze.
Sneezes Reach Up t ...
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The Biology and Mechanics Of Sneezing
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Clarifications
- Mast cells are immune cells found in the nasal passages that detect harmful substances like allergens or irritants. When activated, they release chemicals such as histamine, which cause inflammation and trigger symptoms like sneezing. This release helps alert the body to the presence of irritants and initiates the sneeze reflex to expel them. Mast cells play a key role in the body's early immune response to airborne particles.
- The "sneeze center" is a specific area in the brainstem that controls the sneezing reflex. It integrates sensory signals from the nose and triggers the coordinated muscle actions needed to sneeze. The lateral medulla is part of the brainstem involved in autonomic functions like breathing and reflexes. Damage to this area can disrupt the ability to sneeze, showing its critical role.
- When nasal cells detect irritants, they release chemical signals that activate nearby sensory nerve endings. These nerves send electrical impulses through the trigeminal nerve to the brainstem. The signals reach the lateral medulla, where the sneeze center is located. This triggers the reflexive sneeze response.
- The sneeze begins with a deep inhalation, filling the lungs with air. Next, the vocal cords close tightly to trap the air and build pressure in the chest. Then, the diaphragm and abdominal muscles contract forcefully, pushing air out rapidly. Finally, the vocal cords suddenly open, releasing the air and expelling irritants through the nose and mouth.
- The vocal cords clamp shut to trap air in the lungs, creating high pressure. This pressure buildup allows for a sudden, forceful release of air when the cords open. The rapid expulsion helps eject irritants effectively from the nasal passages. Without this pressure, the sneeze would be weaker and less efficient.
- The diaphragm is a large, dome-shaped muscle beneath the lungs that contracts to increase lung volume. During a sneeze, its sudden, forceful contraction rapidly pushes air out of the lungs. This rapid airflow is essential for expelling irritants from the nasal passages effectively. Without the diaphragm's power, the sneeze would lack the necessary force to clear the nasal passages.
- Narrow nasal passages increase airflow speed, causing air to swirl unpredictably, which is called turbulence. This turbulence helps mix the air, bringing more particles into contact with the nasal lining. The swirling motion prevents particles from passing straight through, enhancing detection by sensory cells. This mechanism improves the nose's ability to trap and identify irritants.
- The initial fluid spray in a sneeze consists of larger droplets that travel quickly and fall to the ground relatively soon. As these droplets move through the air, they break apart into much smaller particles called aerosol mist. Aerosol mist droplets are tiny enough to remain suspended in the air f ...
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Causes and Triggers Of Sneezing
Sneezing is a common physiological response, but its causes and triggers are varied and sometimes unusual. Chuck Bryant and Josh Clark explore several of these causes, ranging from the well-known rhinitis to the more peculiar photic sneezing and "snatiation."
Rhinitis: The Most Common Cause Of Sneezing
Allergies, Colds, Sinus Infections, and Irritants Cause Rhinitis and Sneezing
Rhinitis, which is characterized by inflammation and swelling of the mucous membrane, is identified as the most common culprit behind sneezing. Allergies, colds, sinus infections, and even simple environmental irritants like pollen are common triggers that can cause this condition.
Drugs, Hormones, and Occupations Can Cause Rhinitis
The hosts also discuss how rhinitis can be induced by various drugs, hormonal changes, and occupational hazards. Women may experience hormonal rhinitis due to increased estrogen levels during periods such as pregnancy, puberty, or when taking contraceptive pills. Occupational rhinitis might affect individuals exposed to specific substances in their workplace. Drug-induced rhinitis can develop as a side effect of certain medications, including NSAIDs, beta blockers, and anti-hypertensives. Additionally, geriatric rhinitis, which occurs as submucosal glands atrophy, can make the noses of older individuals more prone to irritation.
Photic Sneezing From Bright Lights
Believed to Be a Genetic Trait
Josh Clark reveals that he is a photic sneezer, usually triggered by bright lights like sunlight. It's believed that the photic sneeze reflex is genetically inherited through autosomal dominant patterns.
Bright Light Causes Cross-Wiring of Pupillary and Sneeze Reflexes
Clark and Bryant further discuss the peculiar condition known as "autosomal dominant compelling helio-ophthalmic outburst syndrome" or "ACHOO." The reflex may be due to a cross-wiring between the pupillary light reflex arc and the sneeze r ...
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Causes and Triggers Of Sneezing
Additional Materials
Actionables
- You can track your sneezing patterns to identify potential triggers and manage your exposure. Start a sneeze diary noting the time, location, and what you were doing when you sneezed, along with any potential triggers you suspect, such as eating, being in a bright environment, or encountering strong smells. Over time, you may notice patterns that can help you avoid certain triggers or prepare for them, like wearing sunglasses to mitigate photic sneezing.
- Create a personalized "sneeze kit" to carry with you, especially if you have identified specific triggers for your rhinitis. Include items like antihistamines if allergies are a trigger, a portable nasal saline spray for dry environments, tissues, and a small flashlight to test if you have a photic sneeze reflex in a controlled manner. Having these items on hand can help you quickly address sneezing episodes and make you feel more prepared and ...
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Cultural and Historical Beliefs and Practices Around Sneezing
Sneezing has been subject to various cultural interpretations and superstitions throughout history, ranging from signs of omen to myths and practices for health.
Sneezing As Good Luck or Supernatural Sign In Cultures
Different cultures have had their own unique beliefs and responses to the act of sneezing.
Ancient Persians Believed Sneezing Expelled a Demon
Zoroastrians, dating back to ancient Persia, believed that sneezing was a sign of the body fighting and expelling an invading demon or spirit, indicating a victory for the person's health.
Sneezing Was Seen As a Death Omen; "God Bless You" Was the Response
In Americal culture, the custom of saying "God bless you" after someone sneezes dates back to the Middle Ages during the Black Plague. Pope Gregory VII suggested saying "God bless you" if someone sneezed because it might be a sign of impending death.
Various Traditions and Superstitions Have Developed Around Sneezing
Across the world, sneezing has elicited various superstitions and traditional responses.
China and Japan: Sneezes Indicate Someone Is Speaking Well or Ill of You
In China and Japan, a superstition holds that sneezing indicates someone else is talking about you; a single sneeze suggests they are saying something nice, whereas two sneezes might mean they are spreading gossip.
Sneezing With Eyes Open Can’t Make Eyes Pop Out
Addressing myths surrounding sneezing, Chuck Bryant notes that contrary to the belief, sneezing with your eyes open cannot cause your eyes to pop out.
Cover Mouth/Nose When Sneezing to Prevent Illness Spread
In terms of public health, there is clear guidance on how to sneeze to prevent the spread of illness.
Droplet and Aerosol Expulsion During Sneeze ...
Here’s what you’ll find in our full summary
Cultural and Historical Beliefs and Practices Around Sneezing
Additional Materials
Actionables
- Create a sneeze safety kit for your car or workplace that includes tissues, hand sanitizer, and a small trash bag to ensure you can follow hygienic practices even when on the go. This way, you're always prepared to sneeze into a tissue and clean your hands immediately afterward, reducing the spread of germs.
- Start a playful tradition with friends or family where you come up with creative, non-religious responses to sneezes that reflect personal inside jokes or positive affirmations, moving away from the "bless you" custom and adding a touch of humor or encouragement to the day.
- Designate a ...
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