A sneeze is an involuntary, forceful expulsion of air through the mouth and nose. It requires the coordination of muscles of the chest, throat and face. It is very common, and not a sign of serious problems.
The resulting stream or air carries tiny particles and droplets, and can reach an estimated wind speed of around 1 000 km/h.
Inhaled particles touching the lining of the nose trigger the release of histamine, which causes the nerve cells in the nose to send a signal to the brain. The result is a sneeze which dislodges the irritating particles which started the whole reflex cycle in the first place.
Anything causing irritation to the nasal mucosa can thus result in a sneeze, and common causes are:
Allergy – allergic rhinitis, allergy to mould, danders, and so on;
Inhaled irritants – dust or powders; and
Virus infections – the common cold, or upper respiratory tract infections.
In some people, sudden exposure to bright light, usually sunlight, can cause a reflex photic sneeze. Even more rare is sneezing after a large meal, triggered by a full stomach. This condition, called snatiation, is a genetically determined.
Many people try to hold back a sneeze, but this is regarded as dangerous: the backflow of air under high pressure can damage sinuses, and in severe cases, can rupture the eardrum. Long term problems could then include hearing loss and tinnitus.
Detailed questioning will usually indicate what triggers the sneeze. If the cause is environmental, removing the cause or limiting exposure to it will help. In the case of suspected allergies, tests can be done to identify the allergen, and appropriate desensitising can be undertaken. Impending or established illnesses are treated. Pets may be the source of allergenic danders, and a home may have a heavy load of mould: dealing with this could be a problem.
In all of the above cases, it may not be possible to remove or avoid the allergen. In these cases, symptomatic treatment can be given. Antihistamines are effective, and special non-sedating types can be used during the day. For chronic conditions, nasal steroid sprays can be very effective.
Sneezing can spray up to 40 000 small droplets and particles at a time. If these particles and droplets contain infectious organisms, the sneeze becomes a very effective aerosol method of disease distribution.
(Dr AG Hall)