Cold exposure, such as being outside unprotected for 10 minutes, can temporarily reduce immune system capacity, allowing latent infections to manifest as illness.

“The point is that this illness is already there, but I can cope with it. So you have a rhinovirus or whatever cause of my common cold and my immune system is coping with it. So let's say I have 100 units of immunity which have to fight to 80 units of a viral or whatever infection. So the immune system dominates the infectious agent and this is a continuous process. Now I go 10 minutes into the cold, the blood flow changes because the cold gives vasoconstriction, so you have less blood. So my 100 units per time can't reach that place and become 75. "Hey," says the virus, puff, and because that goes very fast, half a day or a day later, you have a common cold.”