Blowing one's nose to try and relieve nasal congestion, actually seems to increase and prolong congestion. This is according to a University of Virginia study reported in the NYTimes. They report:
Coughing and sneezing generated little if any pressure in the nasal cavities. But nose blowing generated enormous pressure — “equivalent to a person’s diastolic blood pressure reading,” Dr. Hendley said — and propelled mucus into the sinuses every time. Dr. Hendley said it was unclear whether this was harmful, but added that during sickness it could shoot viruses or bacteria into the sinuses, and possibly cause further infection.
So what are we to do?
The proper method is to blow one nostril at a time and to take decongestants, said Dr. Anil Kumar Lalwani, chairman of the department of otolaryngology at the New York University Langone Medical Center. This prevents a buildup of excess pressure.