Carcinoembryonic antigen values for most smokers are generally around 2.5 μg/L, with a small percentage of smokers > 5 μg/L. Carcinoembryonic antigen is a polysaccharide-rich protein complex, mainly used to assist in the diagnosis of malignant tumors, monitoring the efficacy of treatment, judging the prognosis, tumor recurrence, etc. 96% to 97% of non-smoking healthy people have carcinoembryonic antigen concentrations <2.5 μg/L, and 20% to 40% of the smokers have serum concentrations of carcinoembryonic antigen > 2.5 μg/L, and a small proportion of smokers have a carcinoembryonic antigen >5.0 μg/l. A small percentage of smokers have carcinoembryonic antigen >5.0μg/L. The normal value of carcinoembryonic antigen is <5 μg/L. Some smokers may have carcinoembryonic antigen values >5 μg/L, but this may not necessarily be due to a neoplastic lesion, and needs to be diagnosed in conjunction with imaging tests such as chest CT and PET-CT. Smoking is harmful to human health and increases the risk of cancer, so it is recommended to quit smoking as soon as possible.