The climate that surrounds you, both indoors and outdoors, can impact your asthma. Cold and dry weather is most likely to trigger an attack, so it's helpful to warm your breath in winter by covering your mouth with a scarf. Air that is humid is more easily warmed, so humidity outdoors can be an advantage. However, humidity indoors is a different story. Indoor humidity encourages dust mites and molds to accumulate, and it can lead to worsened asthma due to allergy.

Weather can relate to air pollution. Chemical pollutants from motor vehicle exhaust and fumes combine together on hot days to create ozone. Ozone in the air we breathe is an irritant to our lungs and mucous membranes. It is a common trigger for asthma in children, and it is capable of causing throat and nose irritation, nasal discharge, chest discomfort and cough.

The most dense ozone pollution forms from April through September, particularly in smoggy areas. Other months have half as much ground-level ozone, or less. The air is both cooler and fresher indoors. Air from indoors contains much less dense pollution and ozone than does air from outdoors (a third of the pollution quantity in some study findings).

Researchers have compared the number of people with asthma problems who come to large emergency rooms from day to day through the heavy ozone season. When elevated ozone concentrations are detected ("ozone alert" days), doctors can expect to see more asthma cases than usual during the following day.

Outdoor exercise during days with problematic ground-level ozone levels can be a particular challenge. When you exercise, you breathe heavily and amplify your exposure to environmental pollution, if it is present in high levels. Exercise is a trigger for many asthmatics anyway, but ozone can make symptoms more likely to appear.