About 80% of people are 'secretors' whose blood type can be identified through saliva, sweat, and tears.

The secretor status is determined by the presence of the FUT2 gene, located on chromosome 19. This gene encodes an enzyme called alpha-(1,2)-fucosyltransferase, which is essential for producing the H antigen in bodily secretions. Approximately 80% of the global population possesses at least one functional copy of this gene, making them secretors. This discovery dates back to 1930 when researchers first noticed that some individuals had ABO blood group substances in their saliva.In forensic science, this trait has been historically significant for identifying suspects before the widespread use of DNA profiling. Investigators could determine a suspect's blood type from cigarette butts, licked envelopes, or sweat-stained clothing. For example, in the mid-20th century, secretor status was a primary tool used by the FBI and other agencies to narrow down suspect pools in criminal investigations.Beyond forensics, secretor status plays a critical role in human health and microbiology. The antigens secreted into the gut act as 'prebiotics' that feed specific beneficial bacteria like Bifidobacteria. Studies from institutions like the University of Helsinki have shown that non-secretors often have less diverse gut microbiomes. This lack of antigens can make non-secretors more resistant to certain stomach viruses, like Norovirus, but more susceptible to others, such as Crohn's disease.