A<unk>  is a semi-autonomous, convulsive expulsion of air from the lungs.<unk> ng occurs when a particle (or sufficient particles) passes through the nasal hairs and reaches the nasal mucosa. This triggers the production of histamines, which reach the nerve cells in the nose, which then send a signal to the brain to initiate the<unk> . The brain relates the initial signal and creates a large opening of the nasal cavity.  In certain individuals,<unk> ng can also be caused by exposure to bright light.  This is called the photic<unk>  reflex.
In recent years it has been shown that stifling or holding back<unk> s can cause damage to the sinuses as well as the inner ear.  This is due to the back flow of air pressure. The symptoms of this can include tinnitus, or reduced high frequency hearing, and in extreme cases, rupturing of the ear drum.<unk> s spread disease by producing infectious droplets that are 0.5 to 5 µm in diameter. About 40,000 such droplets can be produced by a single<unk> .
Sneeze
Cough
Cough  
Trench mouth
Breathe odor
Sore throat
Sore throat  
Laryngospasm