Kissing has many benefits including reducing allergy symptoms, benefiting relationships, reducing stress by releasing oxytocin and dopamine, reducing cholesterol levels, increasing longevity, increasing blood flow to the face to give you a healthy glow.
However, kissing in its most mechanical sense, boils down to germ swapping with saliva. Saliva contains bacteria that grow in the mouth. Tooth brushing or mouth wash cannot eliminate the bacteria. These things just slow the growth of bacteria. When kissing, salivary flow with bacteria in it is increased. A Dutch study discovered that a 10-second French kiss can transmit 80 million bacteria between two mouths.
While that may be gross to contemplate, there is a hidden biological benefit to kissing. Our immune system can be strengthened by this transfer of bacteria that we then develop immunity to.
Some bacteria and viruses are not ok to transfer, however. There are contagious illnesses like herpes simplex virus or Human Papilloma Virus that cause pre-cancerous warts. These viruses can stay hidden for years and when a sudden decrease in immune resistance crops up, they break out with destructive lesions.
The bacteria responsible for tooth decay and gum disease are among the 80 million that can be transferred with a kiss. When a baby is born, on the one hand, the mothers kiss can transfer beneficial immune reactions but on the other hand, the contagious bacterial seeds of painful cavities and periodontal disease tooth loss are transferred as well.
For this reason, avoid kissing babies directly on the lips to prevent putting them at risk for tooth decay, or the risk of future gum disease.
Certainly, do not kiss someone if you or your companion are ill or have any mouth sores present. You certainly would not want to transmit those to someone close enough for you to kiss.
If you maintain optimal oral hygiene, which includes brushing your teeth twice daily, flossing once daily and visiting your dentist every three to six months, then the quantity of bacteria you can transmit with a kiss can be reduced to a bare minimum.
As a bonus this will brighten your smile and any bad breath (which is caused by oral bacteria) can be eliminated, making you a more attractive and even better kisser!