Secretor status refers to the presence or absence of water-soluble ABO blood group antigens in a person's bodily fluids, such as saliva, tears, breast milk, urine, and semen. People who secrete these antigens in their bodily fluids are referred to as secretors, while people who do not are termed non-secretors. Secretor status is controlled by the FUT2 gene, and the secretor phenotype is inherited in an autosomal dominant manner, being expressed by individuals who have at least one functioning copy of the gene. The non-secretor phenotype (se) is a recessive trait. Approximately 80% of Caucasian people are secretors, while 20% are non-secretors. Non-secretors have reduced susceptibility to the most common strains of norovirus. Expression of the antigens in the Lewis blood group is also affected by secretor status: non-secretors cannot produce the Le(b) antigen.