Science Friday - How Common Household Products Pollute Our Indoor Air

Episode Date: September 3, 2025

You have probably given some thought to outdoor air pollution, whether it’s wildfire smoke or smog from traffic. You may even check AQI measurements on your phone. But what about the air inside your home? Host Flora Lichtman talks to civil and environmental engineer Nusrat Jung, who studies indoor air pollution, about how we create toxic air without even knowing it, and what we can do to avoid it. Guest: Dr. Nusrat Jung is a civil and environmental engineer at Purdue University.Transcripts for each episode are available within 1-3 days at sciencefriday.com. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

Hey, I'm Flor Lichtenen, and you're listening to Science Friday. Before we get going, we need your help. We are working on a show about SpyCraft. What do you want to know? Is Bond's Aston Martin Eject receipt receipt for real? How much tech can you really squeeze into a pen? What spy gadget questions would you ask a former spy? 8774 Spy. Please call us with your questions. Okay, let's get on with it. Today in the show, So what are you breathing in when you do your hair? When we think about air pollution, we think of smoke, we think of smog, we think of wildfires. But we don't think of everyday hair care products to be causing indoor air pollution. You've probably given some thought to outdoor air pollution. Whether it's smog, from traffic or wildfire smoke, I suspect that many of us are checking AQI measurements on our phone more than we used to. But what about the air inside your house? Today we're talking to a researcher who thinks a lot about indoor air pollution and how we create toxic air without even knowing it and how to avoid it.

Dr. Neustrot-jong is a civil and environmental engineer at Purdue University in West Lafayette, Indiana, and she has a new study out on the toxins released during basic hair care. Newstart, welcome to Science Friday. Thank you, Flora. How are you? I'm well. Let's brush up on your research. findings. This is sort of where hair care products meet heat. What did you find? Our study shows that routine hair-based styling can release billions of nanoparticles into the air just within 10 to 20-minute routine. These particles are small enough to penetrate deep into the lungs. So when we think about

air pollution, we think of smoke, we think of smog, we think of wildfires. But we don't think of everyday hair care products to be causing indoor air pollution. When you talk about sort of basic hair care routines, what do you mean? Is it hair spray? Is it using a blow dryer? What are we talking about here? Right. So hair care routine means utilizing hair care products that are categorized as leave on hair care products, which means you do not wash them off. So we are not talking about shampoo and conditioner because that is something you would use when you are taking a shower. We are talking about gels, creams, hairsprays, oils, any kind of liquids that you would leave on your hair. And are they releasing these nanoparticles

only when they're heated or if you're spraying hairspray, you know, if you're doing aqua net all over your hair, are you also getting that same dose of nanoparticles? So we found that heat tends to exacerbate. the sheer number of nanoparticles released from everyday hair care products. And this is far greater than what we have ever expected to see. When you say far greater, what do you mean? The concentrations are about 10,000, 200,000 nanoparticles per cubic centimeter. So it is not just about concentration flora.

This is important to understand because we studied not just the concentration, but what are you going to receive in terms of dose when you inhale? So our study shows that the exposures can rival highway traffic, which means that highway traffic exposure occurs outdoors, where pollutants are diluted in much larger air volume. In contrast, the hairstyling takes place just inches away from the nose and mouth in an enclosed indoor space where nanoparticle concentrations can build up quickly. but especially this closed proximity and confinement gives airborne nanoparticles a more direct pathway into the lungs.

And the doses can be surprisingly high even during a short styling routine. The heat-based hair styling can release billions of nanoparticles into the air within just 10 to 20 minutes. And they deposit and penetrate deep into the lungs. and the exposure from a single session can rival those from sitting in heavy traffic. Wow, and you're doing it every day? Yes. So do you know what nanoparticles are being generated by these processes, and do we know if they're harmful?

Yes, so our research shows that some of the tiny particles released during heat styling come from the chemical ingredients, particularly siloxins. Siloxanes have been found to lead to adverse effects on the respiratory track, liver, and nervous system of laboratory animals. And when these ingredients are heated, they can break down and form airborne nanoparticles that people breathe in. So these are really the reactions or the secondary mechanism that occurs where they are being formed because they're exposed to heat. It's a chemical reaction, basically. Yes, they become something else than what is listed on the list of ingredients. So I think this is quite serious because breathing them in can irritate the lungs and worsen conditions like asthma.

Over time, you have potential for more serious impacts because they can pass from lungs into the bloodstream. They can spread to other organs. And long-term exposure to these kind of particles with, you know, with chronic respiratory and heart disease. and they have like possible effects on the brain. So these are serious things. Are these products regulated for their aerosol effects and these chemicals that they can generate? So our study is the first to have actually discovered

what is happening during the process of application of a hair care product. So we can only regulate something if we understand that there is a problem. So none of these products are. tested for their emissions, for what happens to them when they are being used. They are formulated only to do certain things, but no, we have never seen that information on any package material. I have never come across it. You know, as I was reading about this, you know, it occurred to me that there's just tons of things that we spray on a daily basis. There are things that we heat up on a daily basis, our cookware. What is your top concern for sort of indoor air

pollutants? Or what are you most interested in studying? So I have been fascinated Floraf with our everyday life and what can we be exposed to. So our discoveries have come from basically observing and then really using cutting edge is instrumentation to measure these everyday activities. to understand what is not visible to us. So air pollution in indoor environments is very, very important because we spend more than 90% of our time indoors. I mean, if you want to think about it, you know, we all, you know, go to sleep in a building. We wake up, we leave our building to go to some other building that may be work or maybe coffee shop, then we go to lunch, we are in another building.

Then we go back home. and that is another building. Maybe we go to a gym later in the evening. That's another building. So as humans, we keep rotating from one building to another. We spend 90% of our time inside buildings. And what happens within these buildings is really important to capture in terms of emissions, cooking activities, or sources of air pollution, using scented products,

candles are sources of air pollution, using heavily centered, cleaning products in your enclosed home environment is a source of air pollution. So we are inadvertently causing all of these chemical reactions in these. Really, we live in boxes that are mechanically ventilated. And if the ventilation conditions are good, even then you are not able to remove all of these pollutants. For example, the pollutants we are talking about today coming from hair care products, The sheer number of nanoparticles are so many that ventilation alone is not able to get rid of it.

So honestly, that's a lot about problems in environments. I think I'd like to make it a little lighter and maybe think about solutions. Well, yeah, I was going to ask. I mean, what are the solutions, do you think? So my number one recommendation is if there is any way you can, and get rid of your chemical mixtures that you are introducing next to your nose and your mouth would be like the best thing you can do. The second best thing you can do is simply reduce the frequency of them.

Try to limit it to once in a week, once in three days. Third would be limit the use of the amount of the product you are applying. Fourth would be to, yes, have ventilation on. I mean, ventilation does help. But then we have other problems, like what you are exhausting from your bathroom exhaust, maybe someone else's air intake in a city like New York. So these nanoparticles, these volatile chemical mixtures, they are cycling through our buildings.

So honestly, the best way would be to ideally remove the source of them. Has your own hair routine changed since you started studying this? Yes. So I am blessed with quite many curly, wavy hair, and I have enjoyed being in these aisles and aisles of so many kinds of hair care products. And believe me, when I say I have used so many of them. And then our team started measuring what is being released, and I think it was one surprise after another surprise

and that surprise turned into a shock and then that shock resulted in simply coming back home and getting rid of every single bottle of spray cream, heat protectant that I had. Really? Yes. I have decided now to be totally natural. So I'm very pleased with having,

changed my hair care routine and simply removed all chemical mixtures from my everyday routine. That says a lot, I think. Yeah, because if you think about it, Flora, your body is not filtering these things out. When people choose to smoke, it's like it's their choice, right? It's like, okay, I am smoking because I want to smoke and you kind of have your own will. But in case of a hair care routine, I mean, I never thought that I'm being exposed to anything at all. Yes. I think that's the fascinating thing about this, that it is a window into how little we really probably know about these kind of exposures, you know, that we didn't even think to wonder about this kind of exposure. Yeah. Heat-based hairstyling should be recognized as an emerging and serious

public health concern. And these exposures occur right where people live, where they breathe, they spend most of their time, and yet they remain invisible and unregulated. We have worked on indoor smoking bans, and we have now come up with volatile organic compound VOC labeling for our building materials. This represents another blind spot that deserves attention. Thank you for taking the time to talk to us. Thank you, Flora. Dr. Nostrad Zhang is a civil and environmental engineer at Purdue University in West Lafayette, Indiana. Thanks for listening. Don't forget to rate and review us wherever you listen. It really does help us get the word out and get the show in front of new listeners. Today's episode was produced by D. Peter Schmidt. I'm Flora Lichtman. Thanks for listening.