How worried should we be about a sneeze? The answer, it turns out, is surprisingly complex. Throughout history, sneezes have been imbued with meaning, from auspicious omens in Homer’s Odyssey to confirmations of divine favor in Xenophon’s Anabasis. Even St. Augustine noted a tendency to return to bed after a sneeze while putting on slippers. But beyond cultural interpretations, what does a sneeze actually signify?
“It’s a physical response to get rid of something that’s irritating your body,” explains Sheena Cruickshank, an immunologist and professor at the University of Manchester. Our noses aren’t just passive entryways. they’re equipped with microscopic hairs called cilia, which actively sense and move to trap irritants. When these cilia detect something unwelcome, they trigger a nerve response culminating in a sneeze – a forceful expulsion of air designed to clear the nasal passages.
The triggers for this response are varied. Allergens, viruses responsible for the common cold or flu and irritants like dust or pepper are common culprits. However, the mechanism isn’t always directly related to a foreign substance. The trigeminal nerve, responsible for sensory and motor functions in the face, can be activated by stimuli like cold air or even the simple act of plucking an eyebrow, initiating a sneeze even in the absence of a true irritant.
Perhaps most curiously, some individuals experience sneezing triggered by bright light – a phenomenon researchers dubbed autosomal-dominant compelling helio-ophthalmic outburst, or Achoo syndrome, in the 1980s. While the precise mechanism remains unclear, it’s understood to be a hereditary and congenital condition.
Why such a dramatic physiological reflex? Sneezing is one of the most explosive involuntary actions the body performs, engaging abdominal and chest muscles to forcefully expel air from the lungs. However, recent research suggests the force isn’t quite as substantial as previously believed. Studies indicate that the visible airflow from a sneeze travels less than a metre, at a speed of approximately 10mph – significantly less than the often-cited comparison to a tennis serve.
Despite its power, sneezing doesn’t cause the heart to stop or eyeballs to pop out, debunking common urban myths. Cruickshank emphasizes that sneezing is fundamentally a protective mechanism. “The first part of any immune response is trying to stop things getting in, but the next is to get rid of things that might be damaging to you. It can go awry in cases of dusty rooms or allergens, but it’s actually a very sensible response that we see in a lot of mammalian species.”
What can a sneeze tell us about potential dangers? Scientists are actively investigating this question. Cruickshank’s work with citizen science projects has revealed a significant link between exposure to air pollution and increased allergy symptoms, including sneezing. “We know pollution damages the linings of your nose and your lungs, and that helps things get in that shouldn’t. So that’s one theory about what’s happening,” she says. “But there’s also evidence emerging that pollution can start to reprogramme your immune system, making you react inappropriately to things.”
Assessing the risk a sneeze itself poses is challenging. Catherine Noakes, professor of environmental engineering for buildings at the University of Leeds and a specialist in airborne pathogens, notes the difficulty in studying an involuntary and infrequent event. “We have a lot more data on the amount and type of particles that we release when we talk, breathe, sing, or cough, because you can make somebody do those things – but we don’t really know much about the relative importance of sneezing.”
Sneezes can transmit infections like colds, flu, and COVID-19, as well as diseases such as tuberculosis, measles, mumps, rubella, chickenpox, respiratory syncytial virus, glandular fever and adenovirus. To minimize transmission, catching a sneeze in a tissue is the most effective method. Covering the face with the elbow – the “vampire sneeze” – is a reasonable alternative. The risk of transmission from contaminated surfaces is variable, with research suggesting the initial concern regarding COVID-19 transmission from inanimate objects may have been overstated.
If concerned about exposure, Noakes recommends wearing an FFP2 mask. However, she emphasizes that the most effective strategy for those experiencing frequent sneezing is to limit potential exposure to others.
a sneeze can be an indicator of environmental factors like pollution, a sign of illness, or simply a response to an irritant. While it’s unlikely to be a harbinger of doom, understanding the underlying mechanisms and potential implications can help us navigate this common physiological event with informed awareness. And, as history suggests, offering a polite “Bless you” remains a thoughtful gesture.
