Everyone has had a cold. Your nose is runny, ears are blocked, and your head feels like it’s filled with cotton balls. Hot soup and tea become the elixir of life, and health is more important than work stress or any diet you’ve been trying to keep. But then something interesting happens; after a few days the symptoms slow down. Less snot runs down your nose, you can hear again, and you can taste! It’s about this time that perhaps you have been invited to a party. Had the cold been at its worst you would never have thought of attending. For one, it’s difficult to have interesting conversation with wet tissues in your hand; plus, you don’t want to make you’re friends sick. But now the worst is over: no more wet tissues and you’re not contagious anymore. Are you?

 Friends have told me that they “aren’t contagious anymore.” I have no idea if it’s true or not, and I’m sure neither do they. All I know is that I don’t want to go to a party where my friend is sick and my health is in doubt with every passing moment.

 Catching a cold

I should be clear at this point that I’m talking about the common cold, which is caused by viruses, and I’m not talking about the flu. Commonly confused with the cold, the flu is a more serious disease, caused by different viruses (and sometimes bacteria).

 There are thousands of viruses around the world. For a person to be infected by a particular virus, a few things have to happen. The virus has to be able to attach to a human, survive inside a human, and start replicating: effectively making virus babies that can attack (infect) other parts of our tissue.

 A virus becomes contagious when it moves from one person to another. Not all viruses can attach to a human; they have to have “hands” that can grab onto human cells. This is why some viruses can infect animals, like horses and pigs, but not humans, because the horse and pig cells look and feel a little different to human cells.

 Each type of virus has different ways of travelling from person to person, surviving inside us and reproducing. Some viruses can move through air (and can infect us as we are speaking), while others need direct touch, or to be ingested in food. The reason that viruses can spread through different environments is because each of these pose different threats to the poor little virus. The air might be too cold or hot, there might be pollutants that kill them, plus if the virus needs live cells to reproduce, they won’t find them in air. Also, some viruses are better at grabbing onto human cells or can survive harsher outside conditions, so they are more contagious than other viruses. With all this in mind, it makes answering the question, “Am I still contagious?” a little difficult, because it all depends which virus has made its happy home inside your body.

 Getting viral

Over 200 different viruses have been blamed for causing symptoms of the common cold, and each year more are identified. (This is why we don’t have a vaccine for the cold). Despite this, there are some usual suspects. Rhinovirus is a well-known virus that causes the common cold. It can survive harsh temperatures and conditions, including our dry and acidic skin. This little bugger is really good at grabbing onto human tissue and reproducing there. Studies have shown that if a family member is infected with rhinovirus it spreads, on average, to two thirds of the other family members. The rhinovirus can easily be spread by contacting contaminated hands and objects, but its great infectious power is that it can live for up to three hours on the skin and other surfaces. Plus, the rhinovirus can spread through air (but it’s not so good at this and often dies in the air before it reaches another person).

 Generally, as long as the viral parts are alive inside the snot coming out of your nose, you are still highly contagious. Usually, your body hasn’t learned how to kill the virus in the initial stages of the cold, so you have the most live virus particles in your snot between the second and fourth days of an infection. In these early days, if you have coughed, or wiped snot from your hand, you will probably be spreading germs by touching your friends, and other things (because rhinovirus can survive on objects).

 The more virus that is alive in your snot, the more contagious you are. But, don’t necessarily be fooled by the fact that you have snot as an indicator that you are still infected with a live virus. Once infected (and contagious) your body will begin to mount an attack on the virus. From the attack, you will keep producing snot, but it will be made of dead virus cells that can’t infect people and excess white blood cells.

 If you are the friend at the party who has just heard a mate say “I’m not contagious”, don’t believe them, not even for a second. Chances are they wouldn’t have a clue whether there are live viruses inside their snot. So if the conversation is fairly dull, get out of there quick-smart, because I’m telling you now -  it isn’t worth the few days of sneezing and coughing ahead. If you are enticed by the conversation, try washing your hands or any parts of the body that have made contact with the person after the conversation. And because rhinovirus can survive on surfaces, washing utensils or benches they have touched is not a bad idea.

 You can’t truthfully tell a friend that you aren’t contagious anymore, unless you’ve had your snot tested for live viruses. And if you haven’t done this, and are spending time with friends while contagious, you are being very rude. Although it’s more socially acceptable, for all of your rudeness, you may as well be picking your friend’s nose.  So if you feel a cold coming on, hold off on the party, don’t touch anyone, and stay at home with your tea. Or go to the party, but be honest. Tell your friends that you are sick, and they could get sick. Then watch the conversation end as they slowly slide away from you.

 If a friend has just told you that they are not contagious, what should you do?

•  Ask them when they started getting symptoms of the cold. If it happened two to four days ago, they are probably still contagious.
• Avoid touching, and try not to stand too close to them, to avoid being infected from virus particles moving from their mouth to you.
• Ask them what colour their snot is (hey, if they are being selfish and speaking to you whilst sick, you can breach social norms and inquire about the colour of their mucus). If it is green or yellow there is a higher chance that they are still contagious. However, if symptoms just started developing mucus may still be clear or white. (Keep reading to find out what’s hot and what’s snot?)