1 When air doesn't path freely through the nose and mouth
People snore when the air doesn't pass freely through the nose and mouth. This could be caused by various reasons.
2 Too much nasal tissue
If a person has too much nasal tissue, air might not pass freely through his nose and the snoring sound might happen as the extra nasal tissue vibrates.
3 The position of tongue
The position of the tongue during sleep can result in snoring. If the tongue moved so that it affected the ease with which air moves, snoring might happen. In such a case, changing the sleeping position can stop the snoring.
4 Poor sleep posture
A poor sleep posture can narrow the throat. When the throat narrows the air passing through it can result in a snoring sound.
5 The throat narrows as people grow older
Older people are more likely to snore because as a person gets older the throat narrows.
6 Men are more likely to snore
Men have narrower air passages than woman and this makes their chances of snoring higher for them. A man who sleeps with poor posture is more likely to snore than a woman who does the same. (See Why do we have dreams at night?)
7 Being overweight
Extra fatty tissues, poor muscle tone and an obese body can contribute to snoring. An overweight person is more likely to snore than a slim person provided that everything else is similar.
8 Alcohol and smoking can increase smoking
Alcohol intake, smoking, and certain medications can increase muscle relaxation leading to more snoring. People who reduce alcohol intake and smoking experience less snoring. (See What Alcohol does to your Brain?)
9 Sleeping on the back
Sleeping flat on your back causes the flesh of your throat to relax and might partially block the passage of air. This leads to snoring.
10 Some pillows can cause snoring
Sleeping on an overly soft or large pillow can cause snoring.