Why does my asthma flare up when i run in cold weather?

Bronchospasm: Cold air can trigger bronchospasm. I recommend either running indoors or using an inhaler before execise.

Maybe uncontrolled: Any flare of asthma suggests that asthma may not be controlled. However, the lungs seem to be particularly sensitive to cold air, although there is some information to suggest that it may be more related to the low humidity of cold air, rather than the temperature itself. Inhaling through your nose while running may help. See an allergist to make sure that your asthma is being optimally controlled.