Your dog licks your face, you pet its head—this is the language of love you repeat every day. But in this back-and-forth, the bacteria in your mouths are quietly completing a two-way exchange. And the consequences of this exchange took researchers an entire study to fully understand.

In 2024, a South Korean research team conducted a study combining oral examinations and genetic analysis on 19 dog owners and their dogs. They sought to answer a seemingly simple question that almost no one had seriously considered:What impact does your daily intimate contact with your dog have on its oral health?

The results were more striking than anyone anticipated.

The study recruited 19 dogs and their owners—the first question alone was unsettling.

At the start of the study, veterinarians asked the owners a simple question: “How often do you brush your dog’s teeth?” Not a single owner answered “daily.” Only about 58% said they brushed once a week, while the remaining 42% brushed once a month or not at all. This finding prompted the research team to dig deeper—because the subsequent genetic analysis would reveal a truth most owners had never considered.

This is not a criticism, but a very common reality. Many owners know in their hearts that they “should brush their dog’s teeth,” but they often assume the dog will resist, they lack time, or “it looks fine,” so they keep putting it off. The problem is: dogs cannot tell you they have a toothache; they simply endure it silently.

How veterinarians “score” a dog’s teeth

In this study, veterinarians used two simple scores to assess each dog’s oral condition. You don’t need to understand medicine—just remember one thing:The lower the score, the healthier the teeth.

The study found that dogs brushed once a week or more had an average dental calculus accumulation score of 0.74 points, and a gingival inflammation score of 0.54 points. For dogs that were rarely brushed, the two scores were 0.83 points及 and0.61 points

The Other Side of Love

Every face lick is love—but also a moment of bacterial exchange between you

The study found that 15 out of 19 surveyed dogs (approximately 79%) had a habit of licking their owner’s face or mouth. For dogs, this is a natural way to express affection and seek connection. To them, every lick is pure love. But science tells us that each such intimate contact is also an opportunity for bacteria to flow bidirectionally between you. Using genetic analysis techniques, researchers identified the bacteria on the dogs’ tooth surfaces one by one. In samples from 10 dogs, they found a total of。

73 different bacterial species

The Journey of Bacteria

Human “cavity-causing bacteria” had taken up residence in dogs’ mouths The researchers specifically searched for traces of this “human cavity bacterium” in the dental plaque of all 19 dogs. Ultimately, in2 dogs

簡單來說：你每天親狗狗、讓牠舔臉，就像家人之間因為日常共同生活而互相傳遞細菌一樣。你口腔裡的細菌愈多，牠嘴裡就愈可能也有同樣的細菌。這不是要你停止愛牠——而是提醒你，愛牠的方式，可以更周全。

狗狗嘴裡還有哪些細菌？部分對人類也有影響

除了蛀牙菌之外，研究還在狗的牙菌斑裡找到了其他幾種細菌，在某些情況下可能對人類造成影響：

「我知道很重要」——但知道，並沒有讓我們動起來

研究裡有一個細節，比任何數字都更令人深思：在 19 位主人當中，有 12 位能夠準確判斷自己的狗牙齒健不健康。也就是說，大多數主人其實是有足夠認知的。

但研究同時發現，就算主人清楚知道狗的牙齒有問題，這個「知道」並沒有讓他們更頻繁地去刷牙。知識和行動之間，存在著一道很深的鴻溝。

但口腔問題的可怕之處，正是它的「無聲無息」。牙結石慢慢積累，牙齦悄悄發炎，細菌在牙縫裡繁殖——直到有一天獸醫告訴你「需要洗牙了，而且要全身麻醉」，你才意識到，問題早就在了。

牙齒壞了，不只是牙齒的問題

很多人以為，狗狗的牙齒壞了，頂多是口氣難聞、吃東西不方便。但事實上，長期的牙齦發炎，會對狗狗的整體健康造成非常深遠的影響。

當牙肉持續發炎，身體的免疫系統會一直保持「戰鬥狀態」，消耗大量能量，同時也可能讓牙齦旁邊的骨頭慢慢受損，長期下來甚至導致牙齒鬆動脫落。

更嚴重的是，口腔裡的細菌一旦穿過發炎破損的牙齦，進入血液循環，便有可能抵達心臟、腎臟等重要器官，引起更嚴重的健康問題。這對於年紀較大的狗狗而言，風險尤其不容忽視。

從今天開始，你可以為牠做的幾件小事

好消息是，改善狗狗的口腔健康，並不需要你變成一位獸醫，也不需要昂貴的保健品。只需要你願意建立幾個簡單的日常習慣：

• 每週刷牙 3 至 5 次——使用狗狗專用的牙刷和牙膏（人用牙膏含有對狗有害的成分，請勿使用）。如果狗狗一開始抗拒，可以先用手指沾牙膏輕輕摩擦牙齒，讓牠慢慢習慣。
• 定期去獸醫做專業洗牙——牙結石一旦硬化，自己在家刷牙是去不掉的，必須由獸醫在麻醉狀態下以超聲波工具清除。建議每 6 至 12 個月評估一次是否需要洗牙。
• 提供潔齒零食或潔齒玩具——這些輔助工具雖然取代不了刷牙，但在兩次刷牙之間，可以幫助減慢牙菌斑積累的速度。
• 主人自己也要保持良好口腔衛生——研究提醒，考慮到人犬之間的細菌傳播，你自己每天認真刷牙和使用牙線，也是在間接保護你的狗。
• 家中有長者或嬰幼兒，留意親密接觸的方式——不必完全禁止狗狗舔人，但避免嘴對嘴的親吻，以及舔觸皮膚有傷口的地方，可以大幅降低細菌傳播的機會。