Why does the rain increase our chances of catching a cold?

Question

Why do I catch cold after getting drenched in the rain? I don't catch cold after taking shower.

What special quality does rain water have which increases the chance of getting a cold?

Answer 1

• Why do I catch cold after getting drenched in the rain? I don't catch cold after taking shower.
• What special quality does rain water have which increases the chance of getting a cold?

To answer this, let's let's first compare (describe) the two situations:

Getting caught in the rain..

• Perhaps you were going for a run, or were walking to class, but either way you're outside, and you got caught in the rain. It's (typically) a little colder outside when raining (and windy), and because you weren't prepared, you got fairly wet all throughout your body, and will remain wet (cooler) for possibly a considerable amount of time (15+ minutes).

Getting out of the shower..

• You're in a bathroom that's (indoors and hopefully at least somewhat) clean, and you yourself are using soaps and shampoos. Perhaps the shower water is hot (and thus the bathroom is at a higher temp by the time you get out), or even just mildly temperatured (a cold shower is fine too). When you get out of the shower, you're (maybe) shivering and cold, but you quickly (within a minute or so) get a towel and dry yourself off, thus removing the cold water. Your body starts getting warmer, and then you get dressed (which further increases body temp).

The reason why people may catch cold after being rained on and not so much after taking (colder than not) showers is because the common cold (rhinovirus) thrives better in slightly cooler tempatures. Rain lowers environmental temperatures, and, when you get rained on, that'll further contribute to a lower body temp. Also, due to the fact that you're outside and not inside, there are (probably) more environmental risks, i.e., a higher prevalency of the rhinovirus. Lastly, if you get caught in the rain then your body is (likely) going to remain colder (wet) for a longer amount of time than if you were just getting out of the shower.

To support these claims of the common cold preferring cooler tempatures, I reference a study that was published in 2014, led by Yale researcher Ellen Foxman, in which they examined the performance of temperature-dependent (immune) defenses and their ability to fight off the common cold at various temperatures. From the study:

Most isolates of human rhinovirus, the common cold virus, replicate more robustly at the cool temperatures found in the nasal cavity (33–35 °C) than at core body temperature (37 °C). To gain insight into the mechanism of temperature-dependent growth, we compared the transcriptional response of primary mouse airway epithelial cells infected with rhinovirus at 33 °C vs. 37 °C.

..

These findings demonstrate that in mouse airway cells, rhinovirus replicates preferentially at nasal cavity temperature due, in part, to a less efficient antiviral defense response of infected cells at cool temperature.

So, ultimately, it's because some of our bodies' defenses against the common cold are temperature-dependent, with those defenses performing more efficiently at higher temps, and less efficient at lower temps.