My nose has been one runny mess all morning. For people who are like that all the time, Mayo Clinic researchers think they've found the culprit.

What the researchers wanted to know: Do patients with chronic rhinosinusitis (also known as chronic sinusitis) suffer from an immune system's overreacting to fungi in the air?

What they did: The researchers tested 18 people with chronic rhinosinusitis and 15 normal people to see how their immune cells responded to four common species of airborne fungi. From nine more patients with chronic rhinosinusitis (and nine more normal people), they collected nasal secretions and tested them for levels of proteins from Alternaria species of fungi and for some chemicals that indicate your body is mounting an immune response.

What they found: When they were grown with extracts of Alternaria alternata, immune cells from 16 of the 18 patients jumped into action, making more of a protein called interleukin-5 than the immune cells from the normal people, which made hardly any. Interleukin-5 is made by some immune cells as a call to arms for other immune cells. Aspergillus fumigatus and Cladosporium herbarum got reactions from fewer patients, and no one reacted to Penicillium notatum. And, just to show that the people with chronic rhinosinusitis aren't getting exposed to more fungus, people with chronic rhinosinusitis and normal people had similar levels of Alternaria proteins in their noses. (But people with chronic rhinosinusitis had significantly higher levels of interleukin-5 and another immune protein in their snot.)

What the study means to you: Airborne fungi are everywhere, so unless you move into a bubble, you're stuck with them. But, if this study is right and chronic rhinosinusitis is often caused by overreaction to Alternaria alternata, it might be treatable with antifungal drugs or by flushing out the sinuses with water to get rid of allergens.

Caveats: This doesn't prove that every chronic sinus infection is caused by an immune system that responds inappropriately to fungus.

Find out more: Links to everything you ever wanted to know about sinusitis, from the National Library of Medicine

A microscope picture of our fungal friend Alternaria alternata: www.uoguelph.ca

The website www.doctorfungus.org bills itself as "your online reference to all things mycological!" and has pretty fungus pictures and enthusiastic descriptions of diseases.

Instructions on nasal irrigation from the University of California–San Diego: www-surgery.ucsd.edu

Read the article: Shin, S.-H. et al. "Chronic Rhinosinusitis: An Enhanced Immune Response to Ubiquitous Airborne Fungi." Journal of Allergy and Clinical Immunology. Published online Oct. 8, 2004.

Abstract online: www2.us.elsevierhealth.com