How cold is too cold?

[weathergal]

.....The point I took from the article is that that if dry weather, not cold weather, restricts airways, then people with asthma should presumably be able to exercise in cold, damp weather. Is that true?

I'm not sure about asthma, but humidity can be deceiving when it's cold. When temperatures are colder the air is able to "hold" less water vapor. Even when it's damp out, the dewpoint (one way to measure water vapor content) is low in the winter time, often in the 20s and 30s or even lower. The temperature is also lower, and thus the relative humidity is high and we can get snow, freezing drizzle, whatever. But during a sunny day in the summer, the air can "hold" more water vapor and the dewpoint and temperature will be much higher, even though the relative humidity is lower and there is no precipitation.

I've probably really mucked up that explanation, but the point is it can be deceptively dry during the winter. So maybe that's what's irritating to people who have asthma.