In Interstitial Lung Disease (ILD) there is thickening of lung tissue, which makes it difficult for patients to breathe and get enough oxygen into their bodies. In addition to shortness of breath, daily cough is very common, with 4 out of 5 patients experiencing this symptom. Cough in particular has a major impact on the ability to exercise, be active, and to simply enjoy life. There are many reasons for cough in ILD, and very often there are multiple overlapping causes. It is hard to improve cough in these patients, with available medicines providing limited relief. One explanation for this gap is an incomplete understanding of cough in ILD. To improve patients' cough there is a need to better understand its cause. In other lung diseases, such as asthma, doctors and scientists have used phlegm tests to measure inflammation in the lung, which helps them choose the right medicine for the right patient. This has not been done for ILD, even though it has recently been found that many patients with ILD and everyday cough have abnormal phlegm tests. Using this strategy in ILD could improve patients' cough and quality of life, and possibly even slow progression of the disease.