Sleeping with wet hair often will increase the risk of cancer? The truth is here

Recently, a piece of news has been widely circulated on social media, claiming that if you "sleep with wet hair", a carcinogenic microorganism will multiply on your scalp, which in turn can increase your cancer risk.

What is going on here? Can sleeping with wet hair really cause cancer? The truth is actually far from the conclusion of this news...

Image source: Weibo screenshot

Let me first state the conclusion. Malassezia is a normal parasite on the surface of human skin and prefers a humid environment, but wet hair does not necessarily produce a large number of Malassezia. In addition, the study did not mention that the Malassezia in pancreatic cancer comes from the scalp. Malassezia is a conditional pathogen and under normal circumstances, it will coexist peacefully with humans.

There is no research that proves that tumor growth is related to fungus on the scalp. The myth simply uses the common factor of "humidity" to link wet hair and cancer.

Sleeping with wet hair can cause cancer

How did this rumor come about?

If you open this article, you can find that the author has seriously taken out a 2019 Nature magazine paper as a basis. There is nothing wrong with this paper itself: the authors found that the cancerous process of some tumors is often accompanied by microbial imbalance.

There is nothing wrong with the research itself. Image source: nature.com

Through their research, they found that pancreatic ductal adenocarcinoma and fungi are closely linked - compared with normal pancreatic tissue, the level of fungi in the tumors of patients with this cancer increased by about 3,000 times! From the analysis, these fungi were clearly rich in members of the genus Malassezia.

In order to understand the causal relationship between these fungi and cancer, the researchers further explored the mechanism behind it. They found that if these fungi are killed, they can play a certain protective role in the mouse cancer model. Similarly, if these fungi are transplanted into the mouse disease model, the process of cancer can be accelerated. Based on these findings, the researchers said that these pathogenic fungi can promote the occurrence of pancreatic ductal adenocarcinoma through some molecular mechanism.

The fact that this study was published in Nature certainly shows its rigor and reliability. But what does this have to do with "wet hair"? The news did not provide clear evidence, but only said that Malassezia likes a humid environment, and freshly washed hair is of course also humid. In other words, just by relying on the common factor of "humidity", the author of this news gave full play to his imagination and linked wet hair and cancer together.

Why is this news unreliable?

If we read this Nature paper carefully, we will find that the way Malassezia promotes the development of cancer is difficult to link to hair.

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The authors of the paper conducted an experiment in which they tagged fungi with fluorescent proteins, allowing them to glow noticeably under a microscope.

In this way, they found that fungi can "run" from the intestines to the pancreas and promote tumors. As members of the digestive tract, the movement of fungi can be said to be a visit between neighbors. It takes much more effort to run from wet hair to the pancreas.

There is also no clear evidence that humidity can breed Malassezia. If there is any factor that can promote the growth of this fungus, fat is an essential nutrient, which can also explain why this bacteria often causes skin infections - they like the oil secreted on the skin.

Because of this, regardless of whether the hair is damp or not, the number of Malassezia on an average person's head can be as high as tens of millions. If we follow the logic in this news, everyone's cancer risk is probably soaring every moment.

How to correctly understand a cancer study?

The reason why this news, which is full of doubts at first glance, can still go viral may also reflect the fact that ordinary people do not understand cancer research and often believe exaggerated conclusions based on the one-sided words of self-media.

When it comes to how to correctly understand cancer research, perhaps it should be divided into several points. One is the research on whether a certain substance can cause cancer, which also includes the Malassezia mentioned in this article. Generally speaking, to prove that a certain substance causes cancer, sufficient evidence is still needed - not only to find its carcinogenic mechanism in animal studies, but also to confirm the same carcinogenic mechanism in humans.

Back to the Nature paper, most of the research was actually conducted in mouse disease models. In order to simulate human cancer, these mice have undergone many modifications and have certain special features. The results observed in these mice cannot be simply extrapolated to humans. As for whether humans will be affected, more, longer, and more in-depth research is needed to confirm.

Please, we mice are different from you humans. Image from pixabay.com

Another type of cancer research may be related to cancer treatment, such as when cancer will disappear, or when scientists have created a drug that can completely cure cancer. If we break down these studies, we will find that most of them are also from animal experiments or even cell studies.

There are a few sayings in the pharmaceutical industry, one of which is "If humans had the same physiology as mice, cancer would have been cured long ago." This saying shows that positive results in animal research do not always translate to humans.

As for cell research, it is even further away. A joke goes like this: "If someone tells you that a certain drug can kill cancer cells, remember that boiling water can also kill cancer cells." A drug that can kill cancer cells may not necessarily work in the human body. It may be easily degraded by the body, or it may not be able to reach tumors buried deep in the tissues, or it may be too toxic and unsuitable for human use.

The reason why these rumors appear is largely because some media reports use exaggerated language to attract attention. In a sense, it is more appropriate to read these stories as a joke. After all, there are only a dozen or twenty new cancer drugs released every year worldwide, which shows how difficult it is to understand and treat cancer. If there is a "blockbuster" cancer news every now and then, it is probably not as blockbuster as it claims.

Summarize

Although this rumor seriously states that wet hair will cause Malassezia to multiply, and cites a paper in Nature to prove that Malassezia can promote the development of cancer, the premise that "wet hair will produce a large number of Malassezia" may not be true.

On the contrary, no matter whether the hair is dry or wet, every normal person has a lot of this kind of fungi on his head. What's more, a study in Nature magazine found that in order to promote the occurrence of pancreatic cancer, microorganisms must move from the intestines to the pancreas. These two parts are also far away from the hair. Looking to the future, if we encounter news such as simple living habits can cause cancer, we can first judge whether the content is well-founded or just generating anxiety. If the news does not talk about the animal model of the study, the sample size, the limitations of the study itself, the difference between causality and correlation, and the conclusions cannot be infinitely extrapolated, then when we read this kind of news, we must be careful to prevent being deceived.

Of course, if we are worried, we can consult doctors and other professionals in related fields. Their answers are obviously more authoritative.

References

[1]https://www.nature.com/articles/s41586-019-1608-2

[2]https://en.wikipedia.org/wiki/Malassezia

[3]https://zh.wikipedia.org/wiki/%E5%9B%BD%E9%99%85%E7%99%8C%E7%97%87%E7%A0 %94%E7%A9%B6%E6%9C%BA%E6%9E%84%E4%B8%80%E7%B1%BB%E8%87%B4%E7%99%8C%E7%89%A9

Planning and production

This article is a work of Science Popularization China-Starry Sky Project

Produced by | Supervised by the Science Popularization Department of the China Association for Science and Technology | China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.

Author: Ye Shi Popular Science Creator

Reviewer: Tang Qin, Director and Researcher of the Science Popularization Department of the Chinese Medical Association