Leaky homes need more energy to keep warm or cool. Sealing the gaps in a house, or increasing airtightness, is a common tip to reduce energy consumption, as well as make the house more comfortable to live in. However, people need a certain amount of fresh air in their homes to maintain air quality, and concerns have been raised that increased airtightness may have the unintended consequence of reduced indoor air quality (IAQ). Our review explored the recent literature to answer the question “What impacts does increasing airtightness have on mould, condensation and measures of indoor air quality?”