If you have a blocked or runny nose, chances are you’ll reach for a tissue or hanky to clear the mucus by having a good blow. But do you go for one nostril or two? Hard blow or gentle? It turns out that some ways are more effective (and less risky) than others.
The three most common reasons for extra mucus or snot are the common cold, sinusitis (infection or inflammation of the sinuses, the air-filled spaces inside the face bones) and hay fever. Each of these conditions cause the lining in the nose to swell up, and to produce extra mucus to flush away infection, irritants or allergens.
Both the swelling and extra mucus lead to nasal congestion. This is when the narrowed passages increase the effort of breathing through the nose. Clearing the mucus by blowing the nose should reduce this congestion somewhat.
At the beginning of colds and for most of the time with hay fever, there’s lots of runny mucus. Blowing the nose regularly prevents mucus building up and running down from the nostrils towards the upper lip, the all-too-familiar runny nose.
Later in colds and with sinusitis, nasal mucus can become thick, sticky and harder to clear.
Think of “snotty nosed kids”, in particular infants or toddlers who haven’t yet learnt to coordinate the mechanics of blowing their noses. They tend to repeatedly sniff thick mucus back into their nose or allow it to dribble down their upper lip.
Keeping this mucus (rather than blowing it out) is thought to contribute to a cycle of irritation that causes the snotty nose to persist for weeks or longer.
This may be due to the retained mucus acting as a good “home” for bacteria to grow in, as well as fatigue of the “hairs” (cilia) that cleanse the nose by moving along mucus and carrying with it irritants, inhaled debris and bacteria.
Thick retained mucus is also more likely to be transported to the throat rather than gravity working it from the nostrils, leading to throat irritation and possibly a cough. This is the mechanism behind the most common cause of prolonged cough after a viral infection or hay fever, known as the post-nasal drip cough.
So it makes sense to encourage people to blow their nose to remove unwanted mucus.
Rare risks if you blow too hard and too often
Although extremely rare, there are a few examples in the medical literature of people blowing so hard they generated pressures high enough to cause serious damage. In most of these cases people had underlying chronic sinusitis or an existing weakness in the structure they damaged after blowing too hard.
These injuries included fractures of the base of the eye socket; air forced into the tissue between the two lobes of the lung; severe headache from air forced inside the skull; and rupture of the oesophagus, the tube that sends food to the stomach.
One study looked at the pressures generated when people with and without a range of nasal complaints blew their noses.
People with chronic sinusitis generated pressures significantly higher than people without a nasal complaint, up to 9,130 Pascals of pressure. They also found blowing by blocking both nostrils generated much higher pressures than blowing with one nostril open.