What Causes The Common Cold?

17:24 minutes

Design by Daniel Peterschmidt


The common cold is an unwelcome yet familiar visitor this time of year. But how much do we really know about it? The term “common cold” is actually a catch-all for several different families of viruses that give us cold-like symptoms. The most common type is a small RNA virus called a rhinovirus, made up of just 10 genes. Researchers think it most likely originated as an enterovirus, a virus most commonly found in the low pH environment of the human gut, that mutated and developed an affinity for the comfy moist confines of the nose and throat.


So what about the elusive “cure” for the common cold? Even if researchers could develop a vaccine for the three species of rhinovirus that cause the majority of colds, we could still be susceptible to one of the other families of viruses, including the coronavirus, the type of virus responsible for Middle East Respiratory System or MERS, and which originated in camels.

Fred Adler, a professor of mathematics and biology at the University of Utah, explains what we know about the history of the human rhinovirus. And Jeff Bender, a professor of public health at the University of Minnesota, clarifies the viral relationship between humans and animals, including whether it’s possible to exchange colds with your pets.

Images via Shutterstock

Segment Guests

Fred Adler

Fred Adler is a professor of Mathematics and Biology at the University of Utah in Salt Lake City, Utah.

Jeff Bender

Jeff Bender is a professor of Public Health in the College of Veterinary Medicine at the University of Minnesota in St. Paul, Minnesota.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. Know thyself. KnOW thy enemy. You might be familiar with that line from Sun Tzu’s, The Art Of War, but it’s not exclusive to the battlefield. It could refer to a political opponent or an opposing sports team or a cold. That’s right, this hour we’re getting to know the enemy within, the common cold, starting with, where does it come from?

Does it have any weaknesses? How does it spread? Will we ever get our hands on that secret weapon, a cold vaccine? That’s what we’re going to be talking about, lots of stuff. Our number 844-724-8255. You want to talk with us, 844-724-8255. Or you can tweet us @scifri.

Let me introduce my guests. Fred Adler is Professor of Mathematics and Biology at the University of Utah. Jeff Bender, Professor of Public Health and the College of Veterinary Medicine at the University of Minnesota. He joins us via Skype. Welcome, gentlemen to Science Friday.

JEFF BENDER: Thank you for having us.

FRED ADLER: Thank you.

IRA FLATOW: You’re welcome. Fred, when we use the term, common cold, it’s really a catchall for many different families of viruses, is it not?

FRED ADLER: That’s correct. There’s at least six families of viruses that cause common colds in people and they’re actually quite hard to tell apart from your own symptoms.

IRA FLATOW: So you can’t tell by what kind of– I’m not going to get gross, mucus is coming out or sneezing, which kind of cold virus you have.

FRED ADLER: In general, no. Usually the most severe things caused by influenza are distinguishable because you’re so sick. But most of the other colds are fairly similar in the way they play out.

IRA FLATOW: Jeff, what do we know about where these viruses come from?

JEFF BENDER: We often speculate that many of our novel viruses come from animals. Sorry, am I getting feedback?

IRA FLATOW: No, we hear you fine.

JEFF BENDER: Sorry. We often speculate that many of these novel viruses come from animals, and many do. And I would also argue many of these come from people, and are actually well adjusted in people. And so there seems to be this constant interchange historically, a kind of shared microorganisms that we’ve had historically. However, we have seen this concern recently about some of these viruses jumping between animals and people.

IRA FLATOW: How do they do that? Do we come in contact with them directly or their droppings? How does that happen?

JEFF BENDER: Oftentimes it’s with direct contact with the animals themselves. And thankfully, when you think about most of the cold viruses, we think about rhinoviruses and adenoviruses and metapneumoviruses viruses. And these ones are actually have what we call a high species barrier, very difficult to jump. But basically, sometimes there is that time when it does jump high enough to get over that species barrier to allow for that interchange. And that might be through direct contact with the animal itself

IRA FLATOW: Fred, what is it about the rhinovirus and rhino means nose, right?


IRA FLATOW: That makes it so well adapted to humans?

FRED ADLER: I think there’s a few things. One as Jeff just said, it’s perfectly human specialized. So it’s good at its job because it mainly does one thing. Another is that it seems that it’s evolved from viruses enteroviruses that live in our gut. And it pops up periodically, loses its ability to survive in your gut, and then takes over your nose and transmits itself there. And third. There’s this huge diversity of them, at least 150 types of it. So you have a long life to look forward to getting fresh new rhinoviruses.

IRA FLATOW: But does that mean, you know, this is a question we get asked and I’ve asked all the time. I’ve had a family of kids. If I get a cold and my kid gets the cold and I get over the cold, am I immune to the cold I just gave it to the kid?

FRED ADLER: It depends. So rhinovirus seems to be unusual in that you get some degree of immunity, but not perfect immunity. Influenza, as a much more severe disease, tends to give perfect immunity for the rest of your life. So rhinovirus immunity, for reasons that are not fully understood, fades over time. And so, not only are there 150 different rhinoviruses, you can get over the course of your life, you can get them more than once.

IRA FLATOW: And so is that the total number of viruses or are there subsets of these viruses and other subsets that go on and on?

FRED ADLER: It’s hard to know exactly how many there are. People have now taken to characterizing them by genetic sequencing. And once again, they characterize about 150 rhinoviruses. I don’t think there are that many others, to tell you the truth. And then there’s roughly 50 other virus types in these other families that can also cause these colds that are so hard to tell apart.

IRA FLATOW: Is that one of the problems in developing a vaccine for a cold virus, there are so many viruses?

FRED ADLER: Yes that’s right. So there’s been some exciting new trials just came out this year on a vaccine. And they managed to pack 50 different types into one vaccine and showed a good response at least in mice and in rhesus macaques. And so it is possible that somebody could load up a vaccine with a lot of these different common colds and induce pretty effective immunity.

IRA FLATOW: Jeff Bender, is it possible to trace back in history when viruses started spreading from animals into humans?

JEFF BENDER: Yeah. I think for some of these, we’re getting the tools to better detect when we see the divergence or change over time. Some of these viruses are quite old or actually some are actually quite new. I think a good example of one that manifests itself with some common cold system is the metapneumovirus. And I think it’s speculated that it’s probably in the last couple hundred years that transmission probably from birds to humans occurred. But again, I think we have a lot to learn here still regarding when and how often these interchanges occur.

IRA FLATOW: Donna Henderson tweets in, wants to know why is it called a cold? When you think about it, how did that start?

FRED ADLER: Traditionally it’s because they’re associated with winter. And so people assume that cold caused colds. And rhinovirus itself is not that actually tightly associated with the winter season. People get rhinoviruses all year. We just think of them differently in the summer, and there may more annoying because you’re not supposed to get colds in the summer. But once again, there’s some other recent really exciting data showing that the tissues in our bodies and our noses that are not quite as warm as the rest of our body are more susceptible to getting infected. And so maybe there is a real association between cooler temperatures and being susceptible to getting infected by colds.

IRA FLATOW: Yeah, I remember we had a story on years ago where we found out that even just having a warmer climate, I mean, I remember the numbers were something, 93 degrees and 86% humidity or something like that, that the viruses don’t survive well in that kind of heat and humidity. Any truth to that?

FRED ADLER: I’m not certain about that it seems to vary a lot from virus to virus, what sort of external conditions they can tolerate. This new work is more about how our cells that have to spend a lot of their time fighting off viruses are less capable of doing that when they’re slightly chilled.

IRA FLATOW: That’s because our body’s immunity is down a little bit when we get cold?

FRED ADLER: Exactly, yeah, the functions of cells like interferon that you’ve probably heard about are reduced when those cells are not at typical body temperature.

IRA FLATOW: I like that. Explains a lot. So Jeff a lot of people want to know, can you give your cold to your pet or vice versa?

JEFF BENDER: That’s a good question. I think Fred really has done a good job to say that many of these viruses that we associate with colds are really species specific and really well adapted to people for the most part. And so the ones that we’ve been talking about specifically rhinovirus or adenovirus. These really are human specific and so the chance that we can get something or give something to our pet is pretty unlikely.

In fact, the opposite sometimes happened is that we’ve given some things to our pets. And I think probably most recently we’ve seen this discussion about influenza, especially when we had the pandemic of 2009. There were the number of reported cases of basically pets actually picking up influenza from there probably sick caretakers or sick human caretakers.

IRA FLATOW: Let’s go to the phones. 844-724-8255. Let’s go to Minneapolis, to Wes. Hi, Wes. Welcome to Science Friday.

WES: Hi. Thanks for having me on.

IRA FLATOW: Go ahead.

WES: My question was if you were to let’s say live in a remote island in the Pacific, would you get a cold or would somebody else have to show up there to spread the virus to you?


FRED ADLER: Somebody else would have to show up. So there’s various anecdotes from the Antarctic, like the Shackleton expedition. Those guys did not get colds because there were so isolated that their population wasn’t large enough to support colds at all. And there’s other more recent studies in the British Antarctic surveys showing that they became actually increasingly susceptible to getting colds because they went for months or years without being exposed.

IRA FLATOW: Could a bird show up and bring the cold to you?

FRED ADLER: As Jeff pointed out, most of these colds couldn’t come from a bird. I guess if you’re unlucky and an avian influenza showed up, that would be a disaster on your remote island.

IRA FLATOW: Are there diseases, Jeff, that we do need to worry about possibly getting from our pets?

JEFF BENDER: For the most part, no. You know, just simple things that we do can put us at risk. And this gets into some basic hygiene things, which is good to remember even for the common cold. And that gets into good hand hygiene. The other thing I often tell folks it’s probably not a good idea to let your pet lick your face or to lick them, or basically potentially share things that they might have and more of some of the enteric bacteria or other things that I’m more worried about in transmission versus probably a cold virus or something along those lines.

IRA FLATOW: Can dogs get the flu, things like that?

JEFF BENDER: They do. In fact, in the past year there’s been a fairly substantial outbreak of canine influenza. So there are specific strains that we see in dogs. The good news is that we haven’t seen that particular strain manifested in people. But it’s a good idea that we watch for these viruses because we know that sometimes they’re sloppy in their replication and there are potential opportunities for interchange of those viruses between animals and people.

IRA FLATOW: What do you think the most misunderstood thing about– I’ll ask both of you –about catching or keeping a getting rid of a cold is?

FRED ADLER: Hard to say.

IRA FLATOW: Is it because there’s so many misunderstood things you can’t narrow it down?

FRED ADLER: Yeah, I guess one of the things I think of is people who claim that they’ve never had a cold in their life. And it seems extremely unlikely there’s anyone who’s never had a cold. There maybe people for whom the symptoms are so mild they don’t notice them, and there are many undiagnosed or undetectable viral infections in people. But the idea that I’m 93 and I’ve never had a cold, I think is pretty much impossible.

IRA FLATOW: Go ahead, I didn’t mean to interrupt your–

FRED ADLER: That’s it. That was my main misconception I can think of. I mean there’s all the stuff about the various folk remedies, but I’m not expert on whether or not some of those in fact work.

IRA FLATOW: We’re going to get into that a little bit later in the program. Here’s a tweet that came in. It said from Tweedle-Dee. It says, I heard that cold viruses mutate their coats so fast that they can duck the immune system and reinfect. Is that true?

FRED ADLER: They mutate very quickly but not so fast as to reinfect. And most of the viruses we’ve been talking about have extremely high mutation rates, like 10,000 or 100,000 times faster than us. So they’re very poorly built in general. But even that is not enough for them to completely change their shape. The way that the most dangerous influenza pandemics have emerged is through changing their external coats. But that’s something that we see happening only every two or three years.

IRA FLATOW: Let’s go to Lindsey in Lubbock, Texas. Hi, Lindsey. Welcome to Science Friday.

IRA FLATOW: Hi. My question is I’ve always heard that we get a cold in the winter because we tend to be indoors near other people bore that in the summer where we’re all walking around outside. Is that true?

FRED ADLER: I would say yes. One of the primary factors in triggering the spread of colds and other infectious diseases kids going back to school. And that does do exactly what you say, concentrate them indoors. The other factor that does seem to have some support is vitamin D, that if we spend less time outdoors we get less vitamin D from the sun and vitamin D is important in keeping our immune system active.

IRA FLATOW: And the idea that it’s cold out and that lowers our immunity perhaps to a virus attack? Does that hold any water?

FRED ADLER: I agree.


FRED ADLER: Yeah, I mean I don’t know. As far as I can tell, the evidence is difficult to obtain, because these viruses are so hard to study outside of the body. But I think that element, that is the viruses survive better outside of the body and what we were talking about before, the chilled tissues are more susceptible are all components of this.

IRA FLATOW: So when your mom told you to wear a jacket and bundle up warm, she was right?

FRED ADLER: Yeah, pretty much.

IRA FLATOW: I’m Ira Flatow. This is Science Friday from PRI, Public Radio International. Talking with Fred Adler and Jeff Bender about the common cold, trying to get to as many myths in whatever way. You mentioned it was so hard to study viruses. Why is it so hard to study them?

FRED ADLER: They’re very small. So they’re hard to see and it’s hard to study. Genetic methods have made it much easier to study them now. So a lot of the recent studies can just take swabs out of people’s noses and see what viruses are in there. But to figure out what they’re actually doing is much more difficult. And you really have to follow people over time. And to study transmission is very hard because it’s tiny numbers of viruses that are involved and figuring out exactly where they came from, were they are sitting on a table, floating around in the air, on your dog, it’s just hard to trace them back.

IRA FLATOW: Jeff, is it likely we could see a new virus spread from animals into humans today?

JEFF BENDER: Yes, actually just to build on Fred’s comment too about why some of this is so difficult to study, the mere fact that there might be well over 200 different viruses that are associated with the common cold makes it difficult. And is it just one or is it actually many of them working in concert as well? Do we have kind of multiple infections or multiple viruses causing infections as well?

So I think that when we think about this, we’re starting to get the tools, but frankly we don’t really understand in a sense the microbiome and its relationship to how these viruses actually grow and persist as well. So it really highlights that complex system.

IRA FLATOW: You’ve touched on our favorite subject. Just threw that in because you knew we liked it. Getting back to my question about is it likely we could see a new virus spread from animals into humans today?

JEFF BENDER: The answer is yes. I think that we’ve been seeing that, especially lately. There’s been a number of recent events that have highlighted some basically opportunistic viruses that have changed and mutated. And I think some specific ones are something like severe acute respiratory syndrome or SARS, if you recall, or even currently the Middle East Respiratory Syndrome Coronavirus. So both of these are coronaviruses. They have an animal host and so those are good examples of where we’ve seen that spill over occasionally from animals to humans.

IRA FLATOW: Question, we’ve all wondered about a tweet from Gene Landerville says, what about feed a fever, starve a cold or is it the other way around?

FRED ADLER: I don’t know what the answer is. My philosophy is if you’re hungry, you should eat.

IRA FLATOW: That means you’re healthy. Feeling better.

FRED ADLER: Exactly. If you feel good enough to eat, go for it. And I do believe in chicken soup.

IRA FLATOW: I only have about a minute or so left with you guys. Anything that we left out that you get asked all the time about colds?

FRED ADLER: Mainly it’s about what we were talking about before in terms of, will there be a treatment? Will there be a cure? How do they get transmitted?

IRA FLATOW: Will we ever have– I’ll ask the ultimate question, will we ever have a vaccine for the common cold, one vaccine or never going to happen?

FRED ADLER: I think yeah, I think there will be a vaccine and there will be a question of whether we’ll use it or not. And it may not seem worth it to people, given that colds aren’t that severe for most individuals.

IRA FLATOW: That’s a good way to wrap it up. I want to thank both of you for taking time to be with us. Fred Adler Professor of Math and Biology at the University of Utah, Jeff Bender, Professor of Public Health at the College of Veterinary Medicine at the University of Minnesota. Thank you and happy holidays to both of you.

JEFF BENDER: Thank you.

FRED ADLER: Thank you.

IRA FLATOW: You’re welcome. Up next, we explore which cold treatments are backed up by science and answer your questions about them. We’ll get to all those things from zinc to vitamin C to chicken soup. So stay with us. We’ll be right back after this break. Stay warm.

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