In people with IPF, the tiny air sacs in the lungs (alveoli) become damaged and increasingly scarred. This causes the lungs to become stiff and means it's difficult for oxygen to get into the blood. The reason this happens isn't clear. Idiopathic means the cause is unknown. IPF has been linked to: exposure to certain types of dust, such as metal or wood dust viral infections a family history of IPF – around 1 in 20 people with IPF has another family member with the condition gastro-oesophageal reflux disease (GORD) smoking But it's not known whether some of these factors directly cause IPF.