Recently, I received an interesting private message backstage, which reads: “I am a female college student. Recently, on my way back to the dormitory from night self-study, I passed by the lake and saw my roommate and her boyfriend kissing very passionately. Perhaps because I have been single since birth, I don’t quite understand why couples can kiss for so long, with saliva that smells bad, plus if the other person has bad breath, wouldn’t they find the other’s saliva disgusting? I’m also curious if kissing can transmit diseases like hepatitis B or AIDS.”

No wonder this student is so curious; let’s clarify these questions once and for all.

Saliva Smells Bad

Why don’t people feel disgusted when kissing?

Everyone has saliva, and when it is in the mouth, you might not notice any smell, but if you wipe saliva on your skin and then smell it, it usually stinks. Why is that?

Actually, saliva generally has no odor in the mouth; it only begins to smell when exposed to air. This is because saliva is more than 98% water, with the rest being proteins, digestive enzymes, and other substances. Once saliva leaves the mouth and the water evaporates, the remaining proteins and enzymes react with microorganisms in the air, producing a foul odor.

Bad breath may be caused by periodontal diseases such as gingivitis or tooth decay, leftover food residues in the mouth, eating strong-flavored foods like garlic or onions, or dry mouth. Other causes might include infections like Helicobacter pylori, diseases, medications, or smoking.

So why don’t couples find each other’s saliva disgusting when kissing?

1. Close Contact: Saliva smells bad when exposed to air, but when couples kiss, their mouths are closed together, limiting air exposure and thus preventing any foul smell.
2. Romantic Blinders: The adrenaline and dopamine released during a kiss induce pleasure and happiness, and the serotonin produced can have numbing and pain-relieving effects, overshadowing any disgust.
3. Out of Sight, Out of Mind: Disgust is often a reaction to visual or sensory inputs, but since saliva is exchanged unseen during a kiss, it’s easier to ignore any negative thoughts about it.
4. Saliva Isn’t Naturally Foul: Saliva is mostly water and contains amylase, an enzyme that breaks down starch into sugars, which can taste slightly sweet.

Diseases That Can Be Transmitted Through Kissing that Many people are unaware

There are concerns about transmitting serious diseases like hepatitis B and AIDS through kissing. However, transmitting hepatitis B via kissing would require both partners to have cuts or sores in their mouths and for one of them to be highly infectious. Similarly, HIV is present in saliva in very low quantities; it would take a significant amount of infected saliva (20-50 mL swallowed in one go) to risk infection.

Instead, pay attention to these four transmissible diseases:

1. Mononucleosis (“Kissing Disease”): Typically transmitted through saliva by kissing, sharing food, or similar activities, causing symptoms like fever, sore throat, and swollen lymph nodes.
2. Respiratory Diseases: During flu season, kissing can spread viruses like influenza or bacteria like those causing tuberculosis.
3. Helicobacter pylori Infection: This bacterium can cause stomach problems and even stomach cancer and can be spread through kissing if it resides in the mouth.
4. Herpes Simplex Virus: Cold sores or fever blisters around the mouth are caused by this virus and can be easily transmitted through kissing.

Three Body Parts to Avoid Kissing Even if you are affectionate, be cautious:

1. Neck: The neck contains the carotid sinus, which helps regulate heart rate and blood pressure. Stimulating this area too much can cause dizziness or even loss of consciousness.
2. Ears: Aggressive kissing or blowing into the ear can change the pressure in the ear canal, potentially causing pain or damage.
3. Belly Button: The skin around the belly button is thin and sensitive, making it prone to pain and infection, particularly from the bacteria typically found there.

In summary, while saliva itself is not foul-smelling, its exposure to air can cause an odor. Couples under the spell of love tend not to notice or mind the smell during kissing. It’s best to avoid kissing parts of the body like the neck, ears, and belly button to prevent health risks.