A buccal swab is a simple, non-invasive collection tool used across genetic science, medicine, and law enforcement to gather deoxyribonucleic acid (DNA) from an individual. The term “buccal” refers to the cheek or mouth cavity, and the swab is gently rubbed against the inner lining of the cheek to collect epithelial cells. These cells provide a reliable source of nuclear DNA for analysis. This method is preferred due to its ease of use, cost-effectiveness, and painless nature, making it ideal for large-scale studies and self-collection across all age groups.
Establishing Biological Relationships
The ease of collection makes buccal swabs the industry standard for kinship testing, which seeks to establish a biological link between two or more people. This analysis is commonly used for paternity testing, but also verifies maternity, sibling relationships, and connections with extended family. The process involves analyzing specific regions of the genome called Short Tandem Repeats (STRs), which are short, repeated sequences of DNA.
Individuals inherit a unique pattern of STR markers—one from each parent—which laboratories compare between alleged relatives. In paternity testing, scientists look for an obligate match, meaning the child must share at least one allele at every tested STR locus with the alleged father. The results are then expressed as a Probability of Relationship, often reaching 99.9% or higher to confirm a biological link.
Screening for Genetic Health Markers
The DNA collected via a cheek swab provides information on an individual’s genetic predispositions for health conditions. This application is part of precision medicine, where genetic information is used to predict risk or guide treatment. One common use is screening for inherited disease risk, involving specific gene variants associated with conditions like cystic fibrosis or hereditary cancers.
Buccal swabs are also used to identify carrier status, determining if a person carries a gene variant for a recessive disorder without having the disease themselves. This information is particularly valuable for family planning, assessing the likelihood of passing the variant to a child. Pharmacogenomics studies how a person’s genes affect their response to medications. Testing for variants in genes like CYP2D6 can help clinicians tailor dosage or select alternative drugs to maximize efficacy and minimize adverse side effects. This screening provides an assessment of future risk or drug response, not a diagnosis of current disease.
Use in Legal and Forensic Applications
In the justice system, the buccal swab is a standardized tool for collecting reference DNA samples from known individuals, such as suspects, victims, or convicted offenders. These samples create a unique DNA profile—a genetic “fingerprint” based on STR marker analysis. This profile is then uploaded to national databases, such as the Combined DNA Index System (CODIS) in the United States.
CODIS allows law enforcement to search for matches between crime scene DNA (the forensic index) and the profiles of known individuals, linking suspects to cases or connecting multiple crime scenes. The use of buccal swabs is favored because it is fast and simple, often replacing the need for blood samples. Due to the legal sensitivity of this evidence, maintaining a strict chain of custody is required to ensure integrity from collection to analysis.
Consumer Genetic Testing for Ancestry
The non-invasive nature of the buccal swab has fueled direct-to-consumer (DTC) genetic testing for ancestry and genealogical purposes. These at-home kits use the cheek swab to collect DNA, which is analyzed to provide users with information about their geographical origins. The most common analysis involves autosomal DNA, inherited from both parents, which provides a broad picture of ancestry and identifies relatives within the last five generations.
Some tests also analyze mitochondrial DNA (mtDNA), passed down through the maternal line, or the Y-chromosome (Y-DNA), passed down through the paternal line. These specialized tests trace deep ancestral lineage by assigning a haplogroup, an ancient genetic population group, to either the direct mother’s or father’s line. Consumer test results can also identify non-medical inherited traits, such as predispositions for hair color, eye color, or athletic capabilities.