Houses often contain invisible, hidden and odorless hazards. For example, radon, an odorless gas, is the second-leading cause of lung cancer. Mold, often hidden, can cause allergies, asthma attacks and frequent infections. Lead, an unseen component of house dust, affects the intelligence learning ability and behavior of children. Carbon monoxide, an odorless gas produced by combustion appliances, can kill. what we bring into and use in our houses can also bring dangerous gases and fumes. Examples include burning wet wood, cleaning with strong store-bought products or storing points and solvents inside the home.