Upper respiratory tract infections, also known as colds and flus, are the most common human diseases. Rhinoviruses, coronaviruses, and influenza strains are to blame. But the severity and duration of these incurable illnesses depends mostly on the age and health of the host. 

We're all much too familiar with the suite of nasty symptoms - headache, sore throat, cough, lethargy, and the messiest symptom of all, the dreaded sneeze. But what causes this funhouse of phlegm? And what, if anything, can be done about it?

Science in Seconds takes a watery-eyed look.

<sub>Host: Rheanna Sand

Photo Credits:</sub>

<sub>CDC Public Health Image Library (public domain); Wikimedia Commons; Flickr

References:</sub>

_{http://download.thelancet.com/flatcontentassets/H1N1-flu/pathogenesis/pathogenesis-4.pdf}

_{http://www.ncbi.nlm.nih.gov/pubmed/19432914}

_{http://www.ncbi.nlm.nih.gov/pubmed/21328251}

_{http://www.ncbi.nlm.nih.gov/pubmed/19906491}

_{http://www.ncbi.nlm.nih.gov/pubmed/18186015}

_{http://www.ncbi.nlm.nih.gov/pubmed/19588387}

_{http://www.ncbi.nlm.nih.gov/pubmed/19047429}

_{http://www.ncbi.nlm.nih.gov/pubmed/22419312}