The most likely cause of lung dysfunction in a young adult non-smoker is a form of asthma
, in which there is spasm of the muscle layer in the airways of the lung. Asthma can be episodic, so can cause quite severe dysfunction one day while the lungs are essentially normal on another.
There also can be some chronic inflammation of the airways (bronchitis) related to some issue other than smoking, The most common would be from allergies. Allergies can actually also contribute to asthma, so it is possible to have a combined picture of asthma and chronic bronchitis from allergies.
Both of these conditions will cause an obstructive pattern on the spirometry.
It is also possible to develop excessive fibrous tissue in the lung, called pulmonary fibrosis
. The fibrous tissue is not as elastic as normal lung tissue, so that the lungs cannot expand normally. This would cause a restrictive pattern on the spirometry. Pulmonary fibrosis can occur as a primary problem (i.e., we cannot identify a cause), but it also can occur in response to inhaling a substance that irritates the lungs, such as asbestos or air that contains certain germs (bacteria or fungus), or as part of a systemic
condition, such as SLE, rheumatoid arthritis, or scleroderma. With your previous home environment, if the spirometry has a restrictive pattern, this could have happened in response to the dust that was inhaled at that time.
If you need any clarification, please let me know.