Could sharing ketchup over french fries be an 'indirect kiss?'

Sharing ketchup with french fries can transfer oral bacteria, and double dipping may be what children jokingly call an indirect kiss. Researchers cited in the article estimated that about 800,000 double dips would transfer as many bacteria as a 10-second kiss. The article also says sauce type matters, with salsa picking up more bacteria than cheese dip or chocolate dip.

Clemson University researchers published findings in the Journal of Food Safety showing that bacteria from the mouth can enter a shared sauce after double dipping.

The researchers estimated that a single double dip could transfer roughly 50 to 100 bacteria between people under conditions involving shared food.

A separate study in Microbiome estimated that a 10-second kiss can transfer about 80 million bacteria between partners.

Immediately after double dipping, researchers detected around 1,000 colony-forming units per milliliter in salsa, about 200 CFU/mL in cheese dip and about 150 CFU/mL in chocolate dip.

A study in the International Journal of Environmental Research and Public Health found that 12 healthy adults who drank unsweetened tea directly from plastic bottles left about 18,000 CFU/mL around the bottle opening and about 8,000 CFU/mL in the remaining tea.

Published Oct 2, 2026 3:42 pm KST

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Sharing french fries with a friend can sometimes lead to a familiar moment: You take a bite, then plunge the same fry back into the communal ketchup.

It may seem harmless, particularly among close friends. Children and teenagers sometimes jokingly call sharing food this way an "indirect kiss." As it turns out, the joke may have a little science behind it.

Bacteria from the mouth can indeed make their way into a shared sauce when someone takes a bite and dips the food again, a practice known as "double dipping."

But how many double dips would it take to transfer roughly as many bacteria as a 10-second kiss?

The answer, based on a playful comparison of findings from separate studies, is around 800,000.

Double dipping can transfer oral bacteria

Researchers at Clemson University in the United States examined how much bacteria could be transferred when a person bites into food and then dips it back into a shared sauce. Their findings were published in the Journal of Food Safety.

The experiment confirmed that bacteria from the mouth can enter the sauce after double dipping. The researchers estimated that under conditions involving people actually sharing food, a single double dip could transfer roughly 50 to 100 bacteria between people.

That figure pales in comparison with what can happen during a kiss.

A separate study published in the journal Microbiome estimated that an intimate 10-second kiss can transfer an average of about 80 million bacteria between partners.

If one assumes that each double dip transfers 100 bacteria, a simple calculation suggests it would take about 800,000 double dips to transfer the same number of bacteria as a 10-second kiss.

The comparison is intended more as a fun illustration than a direct scientific equivalence. The studies examined different circumstances, and the types of bacteria, methods of transmission and experimental conditions were not the same.

Still, the research demonstrates that simply dipping partially eaten food back into a communal sauce can transfer oral bacteria to something other people may subsequently eat.

Salsa, cheese or chocolate: Which picks up the most bacteria?

The amount of bacterial contamination also differed depending on the sauce.

Immediately after double dipping, researchers detected around 1,000 colony-forming units per milliliter, or CFU/mL, in salsa. Cheese dip contained around 200 CFU/mL, while chocolate dip had about 150 CFU/mL.

CFU is a measure used to estimate the number of viable microorganisms capable of multiplying and forming colonies.

The researchers said differences in characteristics such as viscosity may help explain the results. A relatively thin sauce such as salsa can more readily drip off a cracker and back into the communal bowl, potentially carrying more saliva and oral bacteria with it.

However, bacterial levels in the salsa declined over time. The researchers said salsa's relatively high acidity may have made it more difficult for some bacteria to survive.

In other words, a large number of bacteria may initially enter the sauce without necessarily remaining there at the same levels.

What about sharing bottles, chopsticks and spoons?

Drinking directly from the same bottle can also leave substantial amounts of bacteria behind.

In a study published in the International Journal of Environmental Research and Public Health, 12 healthy adults drank unsweetened tea directly from plastic bottles. Immediately afterward, researchers detected an average of about 18,000 CFU/mL of bacteria around the bottle opening and about 8,000 CFU/mL in the remaining tea.

Chopsticks and spoons that have been placed in someone's mouth can similarly pick up oral bacteria.

A Clemson University study found that about 100,000 CFU of bacteria could be transferred to spoons or chopsticks after they were placed in the mouth. Researchers also confirmed that bacteria could subsequently move from the used utensils to food.

But a larger number of transferred bacteria does not necessarily mean a proportionally greater health risk.

What matters is not simply how many microorganisms are transferred, but which microorganisms are involved. If someone has symptoms of an infectious illness such as a cold or the flu, it is best to avoid double dipping into communal sauces or sharing bottles and eating utensils.

This article from Kormedi.com, Korea’s top health care and medical portal, was translated by a generative AI system and edited by The Korea Times.

薯条蘸番茄酱容易传播口腔细菌，而“二次蘸酱”则被孩子们戏称为“间接接吻”。文章中引用的研究人员估计，大约80万次“二次蘸酱”传播的细菌量相当于一个10秒钟的吻。文章还指出，酱料的种类也很重要，莎莎酱比奶酪酱或巧克力酱更容易沾染细菌。

克莱姆森大学的研究人员在《食品安全杂志》上发表了研究结果，表明口腔中的细菌在两次蘸取酱汁后会进入共用的酱汁中。

研究人员估计，在共享食物的情况下，一次两次蘸酱可能会在人与人之间传播大约 50 到 100 个细菌。

《微生物组》杂志上的一项独立研究估计，一个 10 秒钟的吻可以在伴侣之间传播约 8000 万个细菌。

两次蘸酱后，研究人员立即在莎莎酱中检测到每毫升约 1000 个菌落形成单位，在奶酪蘸酱中检测到每毫升约 200 个菌落形成单位，在巧克力蘸酱中检测到每毫升约 150 个菌落形成单位。

《国际环境研究与公共卫生杂志》上的一项研究发现，12 名健康成年人直接从塑料瓶中饮用不加糖的茶，瓶口周围残留约 18,000 CFU/mL 的细菌，剩余茶水中残留约 8,000 CFU/mL 的细菌。

发布于2026年10月2日下午3:42（韩国标准时间）

由 ChatGPT 生成的图像

与朋友分享炸薯条有时会引发一个熟悉的场景：你咬一口，然后把同一根薯条又蘸回公用的番茄酱里。

这种做法看似无伤大雅，尤其是在亲密的朋友之间。孩子们和青少年有时会开玩笑地把这种分享食物的方式称为“间接接吻”。但事实上，这个玩笑背后可能蕴含着一些科学原理。

当有人咬了一口食物后又蘸了一次酱汁时，口腔中的细菌确实会进入共享的酱汁中，这种做法被称为“二次蘸酱”。

但是，需要多少次双重浸浴才能传播与 10 秒钟的亲吻大致相同的细菌量呢？

通过对不同研究结果进行有趣的比较，得出的答案是大约 80 万。

重复蘸取食物会传播口腔细菌。

美国克莱姆森大学的研究人员研究了当一个人咬了一口食物后再将其蘸入公用的酱汁中时，会有多少细菌转移。他们的研究结果发表在《食品安全杂志》上。

实验证实，口腔中的细菌会在二次蘸酱后进入酱汁中。研究人员估计，在人们实际分享食物的情况下，一次二次蘸酱就可能在人与人之间传播大约50到100个细菌。

与接吻时可能发生的情况相比，这个数字简直微不足道。

发表在《微生物组》杂志上的一项独立研究估计，一个 10 秒钟的亲密接吻平均可以在伴侣之间传播约 8000 万个细菌。

如果假设每次双浸会转移 100 个细菌，简单的计算表明，大约需要 80 万次双浸才能转移与 10 秒钟的亲吻相同数量的细菌。

这种比较更多是为了便于理解和举例说明，而非直接的科学等价关系。两项研究考察的是不同的情况，细菌种类、传播方式和实验条件都不相同。

不过，研究表明，即使只是将吃剩的食物蘸回公用的酱汁中，也可能将口腔细菌转移到其他人随后可能会吃的食物上。

莎莎酱、奶酪和巧克力：哪一种最容易滋生细菌？

不同酱料的细菌污染程度也不同。

研究人员在两次蘸酱后立即在莎莎酱中检测到每毫升约 1000 个菌落形成单位（CFU/mL）。奶酪蘸酱中含有约 200 CFU/mL，而巧克力蘸酱中含有约 150 CFU/mL。

CFU 是用于估计能够繁殖和形成菌落的活微生物数量的测量方法。

研究人员表示，粘度等特性差异或许可以解释这些结果。像莎莎酱这样相对较稀的酱汁更容易从饼干上滴落回公用的碗中，并可能携带更多的唾液和口腔细菌。

然而，随着时间的推移，莎莎酱中的细菌数量有所下降。研究人员表示，莎莎酱相对较高的酸度可能使某些细菌更难存活。

换句话说，大量的细菌最初可能会进入酱汁中，但并不一定会以相同的数量留在酱汁中。

共用瓶子、筷子和勺子怎么样？

直接用同一个瓶子喝水也会在瓶子里留下大量的细菌。

发表于《国际环境研究与公共卫生杂志》的一项研究中，12名健康成年人直接饮用了塑料瓶装的无糖茶。随后，研究人员在瓶口周围检测到平均每毫升约18,000 CFU的细菌，在剩余的茶水中检测到约每毫升约8,000 CFU的细菌。

筷子和勺子如果放进别人嘴里，也会沾染口腔细菌。

克莱姆森大学的一项研究发现，勺子或筷子放入口中后，大约有10万菌落形成单位（CFU）的细菌会转移到这些餐具上。研究人员还证实，细菌随后会从用过的餐具转移到食物上。

但是，转移细菌数量较多并不一定意味着健康风险会相应增加。

重要的不仅是传播了多少微生物，而是涉及哪些微生物。如果有人出现感冒或流感等传染病症状，最好避免重复蘸取公用酱料或共用瓶瓶罐罐和餐具。

本文来自韩国顶级医疗保健门户网站 Kormedi.com，由人工智能生成系统翻译，并由《韩国时报》编辑。