When your nostrils are partly blocked, irregular pressure through the nasal passages is created that makes the soft tissue in your nostrils flap.
This can also force you to breath through your mouth, which makes it more likely that your soft palate and uvula (the little flap you see hanging in the back of your mouth) will play the snoring song.
The most common cause of nasal snoring is the flu or seasonal allergies.
However, if you’re a chronic nasal snorer, it’s most likely due to tension in the nasalis, a sphincter-like muscle of the nose.
You can use the nasalis consciously to flare your nostrils.
However, your brain also uses it unconsciously. On a cold day, the nasalis narrows your nostrils to take in less cold air. When you work out, the nasalis flares your nostrils for you to inhale more oxygen. When you go underwater, the nasalis can completely block your nostrils to prevent water intake.
Nasal sprays and strips can be somewhat helpful with problems of the nasalis. You can also try deep breathing or focus on relaxation of the nostrils.
If your self-test reveals your nostrils are the main cause of your snoring and/or sleep apnea, I’ll tell you about other natural treatment options I find more effective.