Kissing is an intimate act that allows for the transfer of bodily fluids like saliva between two people. This brings up an interesting question – if you kiss someone, how long will your DNA stay in their body afterwards?
How DNA is transferred through kissing
When two people kiss, their saliva mixes together. Saliva contains cells from the inner lining of the mouth, known as epithelial cells. These cells have DNA inside them – your unique genetic code that makes you who you are.
So when you kiss someone, you are essentially transferring some of your epithelial cells – and DNA – into their mouth. The same goes for them transferring their cells and DNA into your mouth.
How long does foreign DNA last in the body?
After swapping spit with someone during a kiss, how long will their DNA stick around inside you? Here are some estimates:
- Mouth – Foreign DNA can be detected in saliva for 1-2 hours after kissing.
- Throat – DNA may persist in throat epithelial cells for up to 24 hours after intimate kissing.
- Stomach – Any swallowed DNA is likely to be broken down by stomach acid and enzymes within an hour.
- Bloodstream – Only trace amounts of DNA may transfer from the mouth/throat into the bloodstream and circulate for a short time.
So most of the foreign DNA acquired through kissing is gone within a day. Though specific genes or fragments of DNA could possibly persist longer in the mouth or throat.
Why we don’t incorporate foreign DNA from kissing
An interesting question is – why don’t we incorporate the foreign DNA we get from kissing into our own genome? After all, kissing exchanges saliva which contains entire epithelial cells with DNA inside them.
There are a few key reasons for this:
- DNA degrades quickly – The DNA within transferred cells begins breaking down soon after entering a new host environment.
- No integration mechanism – The body does not have a mechanism for integrating foreign DNA sequences into its own genome.
- Immune response – The immune system recognizes foreign cells and tags them for destruction before integration can occur.
So while we temporarily harbor DNA from kissing partners in our saliva, it does not get integrated into our bodies’ long-term genetic code.
How kissing transfers DNA in special cases
While most DNA from kissing is temporary, there are a few special cases where foreign DNA gets incorporated into the recipient’s body more permanently:
Bacteria
Some bacteria in saliva can take up loose DNA fragments through “horizontal gene transfer.” This DNA may provide antibiotic resistance or other benefits to the bacteria as they colonize a new host.
Viruses
Viruses like herpes, cytomegalovirus, and Epstein-Barr virus spread through contact with saliva. These insert their DNA into host cells where it persists for life.
Pregnancy
In rare cases, small amounts of male DNA from saliva have been found to cross the placenta and persist in a pregnant woman’s bloodstream at low levels.
Cancers
There are also isolated cases of foreign DNA integrating into host cells and contributing to the development of oral cancers.
So while most DNA is temporary, kissing may facilitate rare DNA transfer events with lasting impacts in certain circumstances.
How kissing could transfer ancient retroviruses
Our genomes contain DNA sequences from ancient retroviruses that inserted themselves into our ancestor’s genomes millennia ago. For instance, about 8% of the human genome consists of human endogenous retroviruses (HERVs).
Some HERVs may still retain viral genes that get expressed in certain conditions. So could intimate contact like kissing provide a mechanism for ancient retroviral DNA to spread to new hosts today?
While possible, the risks are low since HERVs have accumulated mutations over thousands of years that prevent active infection. But effects like immune activation or inhibition could potentially get passed on through salivary transfer of viral DNA fragments and proteins.
This avenue of research warrants further study given the volume of retroviral DNA in the human population and the prevalence of intimate saliva contact.
Applications of tracing DNA from kissing
While DNA passed through kissing is generally short-lived, there are some applications of tracing where DNA goes after a kiss:
Forensics
Detecting a suspect’s DNA in a victim’s mouth can provide evidence of intimate contact in crimes. Though kits today look for chromosomal DNA rather than retroviral DNA.
Gene therapy
Salivary transfer may provide a novel route for delivering gene therapies using viral vectors. Some researchers have experimented with using engineered retroviruses to repair genetic defects.
Ancestry
Analyzing HERV sequences in saliva could potentially reveal information about human migration patterns and interaction throughout history.
However, many ethical considerations around privacy would need to be addressed first before applying such techniques.
Conclusion
To summarize, here’s how long DNA sticks around after kissing:
- Most DNA is undetectable after 24 hours
- Viral DNA may persist if infection occurs
- Bacterial gene transfer is possible
- Rare DNA integration events occur in special cases
So while kissing does transfer DNA, most of it is broken down and not incorporated into the recipient’s body long-term. But intimate contact like kissing continues to provide opportunities for rare genetic transmission events, both good and bad.