Question: what are the causes of low oxygen levels in the blood?
Answer: Anemia.
ARDS (Acute respiratory distress syndrome)
Asthma.
Congenital heart defects in children.
Congenital heart disease in adults.
COPD (chronic obstructive pulmonary disease) exacerbation — worsening of symptoms.
Emphysema.
Interstitial lung disease.