Why do stuffy noses get more productive when you’re recovering from getting sick? If the point of a runny nose is to expel the bad germs through mucus, then wouldn’t it make more sense for them to get less productive as you recover because the bad germs are mostly gone?

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Why do stuffy noses get more productive when you’re recovering from getting sick? If the point of a runny nose is to expel the bad germs through mucus, then wouldn’t it make more sense for them to get less productive as you recover because the bad germs are mostly gone?

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Actually, a runny nose is just the result of your body making extra mucus. This is separate from a stuffy nose, which is caused by *inflammation* (which is like swelling, but inside the body in this case). So basically, when our noses and sinuses get irritated — by an illness or allergies — they do 2 things: they produce more mucus and they become inflamed.

As long as your nose is stuffy, there is a lot less room for mucus to drain out and for air to come in. *That doesn’t mean that you have less mucus!* Instead of coming out of your nose, the mucus usually drains down the back of your throat into your stomach. When the congestion goes away, however, the mucus can start finally flowing directly out of nostrils, which is why your nose gets runnier as it gets less stuffy.

I don’t have the answer to this question, but I want to mention that it’s not always good to assume everything in biology has a purpose. Evolution is a flawed and messy process that often comes up with a “good enough” solution, rather than an ideal one. And there are two evolutionary processes going on here. Humans evolve in response to viruses, but viruses also evolve to affect humans in a way that makes it easier for them to spread.

This is entirely speculation, but I’ll give an example of how this *could* hypothetically evolve without having a purpose. It’s good for viruses if you produce a lot of mucus, because then you sneeze, blow your nose, and spread germs. The virus benefits from you producing as much as possible while you’re infectious. When you’re recovering, the virus doesn’t benefit from you producing mucus, but it doesn’t hurt, either. Maybe the easiest way for the virus to make you produce more mucus when you’re sick and infectious also makes you produce more mucus when you’re recovering.

You could make a similar argument on the human end. Producing more mucus during the illness helps flush out the virus. If the response lasts too long, that’s not ideal, but will it actually cause you to have fewer kids and not pass on your genes? Probably not. And if it doesn’t stop you from passing on your genes, evolution doesn’t care.

They don’t always get more productive later in an illness, but what you may have been experiencing is post-viral acute rhinosinusitis. In this scenario, a viral upper respiratory tract infection (a cold) sets up a more prolonged inflammatory process in your sinuses, leading to them discharging for a more prolonged period after the initial illness has cleared up. The mucus doesn’t really exist just to expel bad germs, but it’s the consequence of the inflammation caused by the illness.