There are many reasons why allergies can become worse when traveling. In general, changes in climate can make them worse. For example, a dry climate and low humidity in an airplane or new location.
Traveling to areas with higher counts of pollen, mold spores, dust mites, and animal allergens can impact your allergies. These allergens may also be present on a flight. This is from exposure to other people’s clothing, shoes, hair, and luggage. Accommodations while traveling (e.g., hotels) can also expose people to allergens and irritants. This includes passive tobacco smoke and pollutants.
Additionally, exposure to illnesses from other travelers can make allergies worse. Changes in cabin pressure can worsen nasal congestion. An increase in stress can also affect symptoms.