Listen: A New Definition of ‘Clean’

The upsides and downsides of sterilizing ourselves

On this episode of the podcast Social Distance, the Atlantic staff writer James Hamblin talks about his new book, Clean: The New Science of Skin.

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What follows is an edited and condensed transcript of their conversation.

Katherine Wells: What does it mean to be clean?

James Hamblin: “Clean” started as a religious concept with a strong moral valence. It didn’t become associated with health and hygiene in any real sense until we learned about germ theory about 150 years ago. Since then, it’s been a slow growth of a lot of habits and practices that we sort of associate vaguely with health and hygiene and preventing infectious disease, but in many common uses today, it’s actually just a sort of a judgmental term that we use to say who is acceptable and who is not.

Wells: What was the first recorded instance of the concept of cleanliness?

Hamblin: Variations on cleanliness or purity were part of a lot of rituals. The Aztecs bathed people before killing them just to make sure that the person was pure. Baptisms and similar ceremonies are common in many religions. The point of this cleansing was never to remove microbes; there was no idea of what microbes were, and there wouldn’t be for a long time.

Wells: What made you want to write a book about cleanliness, and why is it coming out during a time of extreme fear over germs?

Hamblin: Well, I started working on this back in 2015 when there was some interesting new science coming out around the microbes that live on our skin. I wrote a story for The Atlantic that centered on a skin-probiotic company, for which I didn’t shower. I’d been leading up to it by minimizing my hygiene routine for a while, and for the story, I tried to see if I could just go with absolutely nothing. That got me into this idea of wondering why we do the things we do and how much of it is really associated with health. So I spent the last few years tracing those ideas and trying to break down the concept. I finished writing it at the end of last year and then this pandemic happened. Which, obviously, I did not anticipate. But I still think the book really holds up.

Wells: What does it mean to be clean today? Are we too clean? Not clean enough?

Hamblin: How would you describe “clean”?

Wells: Germ-free, I think, is usually the way I think of it. Post-soap.

Hamblin: It’s interesting that you think soap kills germs.

Wells: Doesn’t it?

Hamblin: No. Soap is a fatty acid that is combined with a base and heat and results in this product that you see as a bar of soap. It can become liquid depending on what kind of oils you use, but that’s all it is. Anything else that’s added to a soap makes it not a soap. For example, Dove is not a soap. It’s a beauty bar because there are emollients in it. Soap is just a collection of these molecules, called saponins, that will bind to an oil on one end and to water on the other. When you have, say, syrup on your hands and it’s really sticky and it’s not coming off with just water, you use soap and it miraculously washes the syrup off. One end of that molecule binds to the sticky, fatty syrup and the other binds to the water, and it washes away.

The idea that soap kills microbes on your hands is not accurate and potentially bad because the act of removing microbes from your hands comes from a combination of scrubbing water and soap. You know how people are asked to wash their hands for 20 seconds or to sing “Happy Birthday”?

Wells: Yes. I’ve heard that you should sing “Happy Birthday” twice.

Hamblin: Right. You wouldn’t have to do that if the soap was killing the virus like a hand sanitizer, which is killing microbes. The act of washing hands is really about scrubbing—that mechanical force of removing whatever is on your hands.

Wells: I thought the soap disintegrated the coronavirus cell walls?

Hamblin: It can, because the cell walls have some fats in them, but that is not the primary action. It’s really about scrubbing and about washing everything off that whole layer of skin.

Wells: Would you get the same result without soap?

Hamblin: It would be much, much better to wash your hands without soap than to not wash them at all. If you just cover your hands in soap and then hold them under water for a moment, it’s not effective. A good example is toothpaste: You’ve probably brushed your teeth without toothpaste, right?

Wells: I have. Yeah.

Hamblin: Doing that is certainly better than nothing. It doesn’t have that minty freshness, but that mint doesn’t mean your teeth are actually cleaner. Most of the work of tooth brushing is done by the mechanical force. Toothpaste will sort of help remove any really sticky stuff that’s clinging to your teeth, but the brushing is the thing. We should think of hand-washing the same way.

Wells: We’re in a moment where we’re all staying inside as much as we can. We are all trying to avoid contact with surfaces and other people. We are probably more sterile than we would otherwise be. Is that a wholly good thing? Is there such a thing as too clean?

Hamblin: It seems that there is such a thing as being too clean. All those microbes all over you are serving some purpose in shaping your immune system, especially when you’re young. We know that people who have diverse skin microbiomes, just like gut microbiomes, have lower incidences of skin conditions like acne, eczema, psoriasis.

Wells: Those are autoimmune conditions.

Hamblin: Yeah, exactly. The immune system flares up in those conditions. The microbes your body is exposed to shape your immune system. When you are exposed to certain things, your immune system learns that it doesn’t need to flare up and try to mobilize all these inflammatory molecules to deal with the exposure. This is a radical oversimplification, but if your body is not exposed to those things, it’s more likely to overreact. A good example is food allergies.

There’s this thing called the hygiene hypothesis—it’s sometimes called the biodiversity hypothesis. The idea is that when you don’t have biodiversity in your environment and in your exposures as a youth, you are at higher risk of allergic and inflammatory conditions like food allergies or eczema. There’s a famous study in the New England Journal of Medicine that looks at Amish populations. Amish populations don’t have the same rates of allergic disorders as genetically similar populations that have embraced the indoor, urbanized lifestyles that you and I have. Amish people spend a lot of time outdoors and also keep animals, often in places adjoining their houses. So they’re exposed to soil and to all different kinds of species. It is not an isolated, sterile lifestyle.

Wells: So being too sterile makes your immune system paranoid—it overreacts to exposures that aren’t harmful?

Hamblin: That’s the theory. It’s also the environments that we’ve created. If you live in New York and stop showering, it wouldn’t mean that you are really exposed to a healthy mix of microbes.

Wells: You would need to go out and lick a field in which animals graze.

Hamblin: [laughs] Well, it’s not that simple, because there are not a lot of undisturbed microbial environments where you can safely get these exposures. There’s a lot of pollution and actually harmful pathogens out there. Short of moving to a farm, there are some things that we know can help. There’s some evidence of a sibling effect, where people with more siblings have fewer of these allergic and inflammatory conditions. People with pets have fewer, too. You could eat foods that are higher in microbes. I wrote about this in The Atlantic—fresh produce is a natural probiotic. There are microbes inside of an apple that you’re getting exposed to that are not there once you’ve turned it into apple juice. All of these things together will help create a healthy biome and healthy immune system.

Wells: The temptation I’m having here is to think, Well, I should go out and expose myself to a bunch of stuff to build up the immune system. But is it too late for me as an adult?

Hamblin: It would be more difficult than if you were a child, but if you can get out in safe ways, you should. In normal times, being around other people and exposed to pets and the outdoors are the general patterns that keep the immune system healthy.

Wells: You mentioned that most of this sort of training of the immune system happens in childhood. Right now, kids aren’t in school and they’re not seeing people. They’re not going out and about as much. What’s the consequence of that?

Hamblin: I think it’s similar to the consequence of kids not being exposed socially to other people or not seeing the world as much. There are going to be longer-term consequences to that, which we don’t know how to predict yet. But we do know that kids end up more worldly and grounded and intelligent when they’ve had a broad array of experiences in childhood. I think we should think about their biomes and immune systems in the same way. I wish I could tell you how that will play out. I’m not suggesting that people give up any of the targeted practices that are being advised right now, but I think it can be overdone. Your idea of clean can’t mean totally isolated and totally sterile. You need a definition of clean that embraces complexity and plurality and diversity. That is when the term genuinely becomes synonymous with health.