When you are sick with a cold or the flu, you may have a runny nose. Why is it called a runny nose? Because of the mucus flowing and dripping from your nose.

Yucky! But, guess what? Mucus is very helpful.

Just hearing the word is enough to make some people uneasy, but science tells us that mucus is our friend. New research has found that health benefits can come from mucus and viruses.

Our bodies can produces more than a liter of it every day. So what is it?

"Mucus is typically a clear, gel-like substance. It is very slimy. Mucus is a secretion or substance that your body produces, and it produces it to protect itself but also to select for specific bacteria and microbes that actually help you and contributes to your immune system, and it sort of covers and coats almost the entire inside of our bodies.

That is Jeremy Barr, adjunct professor at San Diego State University. He says that mucus is where all of your good bacteria lives and grows.

When you have a virus, it can cause many illnesses. Barr and his fellow researchers studied a virus called "phage."

He says this virus, when mixed with mucus cells in the body, can help protect it against bacteria.

"Phages are a special kind of virus because they only infect and kill bacteria. They don't infect humans or other animals. What our research has shown is that these phages actually stick to mucus layers all throughout your body and by sticking there they work with your body to protect and control the bacterial community that can reside or live in your mucus layers."

Mucus also helps protect your lungs from dust, bacteria, cigarette smoke, exhaust fumes and other intruders.

Barr says the interaction between mucus and phage is constant. And there are health benefits when you have a cold.

"When you get sick, the common cold is actually a type of virus that infects our own cells and so, in that case, changes to your mucus layer could disrupt these phages or...and could sometimes lead to what we call a secondary infection. So you will actually get a bacterial pathogen that will come in and cause an infection after the common cold. We think this is a very important mechanism in your body to keep you healthy and to protect you from bacterial infection."

The group grew human lung cells in petri dishes to produce sterile mucus. They then added the phage virus. Then, they added bacteria. They found that the lung cells were better protected from bacteria than those without the added phage virus.

Jeremy Barr says he hopes the research will bring forth new fields of phage research, even to help prevent food-borne outbreaks like E. coli.

"So we think that if we could use these phages and how they stick to mucosal surfaces and potentially protect against some of these food-borne outbreaks."

So the next time you have a cold, remember your mucus -- along with the phage virus -- is hard at work to make you healthy and keep those harmful bacteria away.

I'm Marsha James.

Marsha James wrote this story for Learning English. Kathleen Struck was the editor.