You might not think too much about your surroundings when you exercise, but they could be the cause of your phlegm. The gym is typically full of chemicals used to disinfect the different machines which you could be sensitive to, while your morning hike opens you up to all the different allergens of nature.
Why do you have allergies? It’s because your body comes into contact with a substance it considers foreign, typically through eating, breathing, or touching. The minute the invader enters your body, your immune system jumps into action by sending out antibodies to identify the substance, which causes you to be flooded with histamine. Within minutes, you can feel inflammation affecting your sinuses, skin, and possibly airways, states the Mayo Clinic. For example, you might start sneezing or notice your nose running. This postnasal drip can lead to phlegm and coughing as you work out. You might even experience watering eyes, notes the Cleveland Clinic.
Inhaled allergens like chemicals, pollens, and perfumes can be hard to avoid. Taking preventive action by using an antihistamine can make it easier to get through your run. It can also be helpful to avoid areas you know are triggers for you, like fields of dandelions. Visiting an allergist can help you to determine the allergen and prevent exposure to it if possible, per the Asthma and Allergy Foundation of America (AAFA).