The proverbial "thick air" indoors has many consequences: 

- Disorders of well-being (headache, fatigue, mood swings, lack of concentration, loss of appetite, nausea, sleep disorders)

- Irritations of the respiratory tract and the eyes

- Allergies and hypersensitivities, impairments of the nervous system

- asthma, diabetes, infertility, cancer

Source: https://www.dropbox.com/s/8f2tzlmzgqowhey/raumluft.org-Info_Air quality_V_2.1.pdf?dl=0