FROM THE PODCAST “THE SMARTEST DOCTOR IN THE ROOM”

A new generation of exposure science reveals how a single strand of hair can preserve a detailed record of the body’s interaction with the environment.

New advances in exposure science suggest that hair may function as a biological archive—capturing traces of nutrients, toxins, and environmental chemicals circulating in the body over time.

In this interview, Dean Mitchell, MD, speaks with environmental epidemiologist Manish Arora, PhD, whose research has shown how hair and other biological tissues can preserve a time-resolved record of environmental exposures. By analyzing these molecular timelines, scientists are gaining new insight into how pollutants, nutrition, and other environmental factors influence human health—from early development through adulthood.

Dr. Dean Mitchell: Dr. Arora, welcome! I have to admit something right up front. For the three decades that I’ve been in practice, I have never used hair analysis in my diagnostic workups. For the most part, I had never heard of a reliable laboratory conducting proper analysis, and I wasn’t sure which conditions would be most helped by using this methodology.

The only area where I had heard hair analysis might have value was heavy metal testing and cancer, but it never really intersected with my work until recently, when I read an article in the New York Times about families in Los Angeles returning to homes affected by wildfires. The paper mentioned your company is doing testing on the toxic exposures in those homes. That really caught my attention.

Dr. Manish Arora: Dr. Mitchell, it’s my pleasure. I’m looking forward to the discussion.

Dr. M: I’d like to start with the basics, because many people—including myself—may be learning about this for the first time. In the article, you were quoted as saying that one centimeter of hair represents one month in a person’s life, and you also said that every other type of lab test—whether it’s blood or urine—is just a snapshot, while hair can map back in time like a molecular movie. Can you explain what you mean by that?

Dr. A: Absolutely. Every part of the human body—blood, urine, saliva, or hair—carries useful information about what our physiology is experiencing. But blood turns over quickly, so in a sense it forgets. If you were exposed to something like lead, that information in the blood begins to fade fairly quickly because the half-life of lead in blood is about a month. That means the signal of that exposure is cut in half in about thirty days. Hair is very different. It does not turn over in the same way. Instead, it preserves information in a stable archive.

The way we can look back in time using hair is actually a simple concept. If you’ve ever seen the cross-section of a tree trunk, you can see the growth rings. Each ring represents a different year of the tree’s life. Hair works in a somewhat similar way. It grows continuously, and those growth patterns capture information about what the body is experiencing at that moment. In hair, we can see growth rings forming roughly every hour. On average, hair grows about one centimeter per month, and within that centimeter there are roughly 1,000 growth rings. So if I analyze one centimeter of hair, I can see information from the entire past month.

Dr. M: That’s remarkable. Most people, myself included, tend to think of hair as cosmetic. We worry about whether it’s thinning or falling out, but we often assume hair itself is essentially dead tissue. What you’re saying is very different—that hair can actually tell us a great deal about our internal physiology.

Dr. A: That’s right. Hair isn’t just dead tissue. As hair grows, it absorbs information from the bloodstream. Molecules circulating in the blood—minerals, toxins, hormones, and other compounds—are incorporated into the hair shaft. Once they’re deposited there, they remain stable. Each segment of hair becomes like a capsule of information representing a specific moment in time.

Dr. M: So in theory, you could measure things like minerals in the body—zinc, copper, calcium—just by analyzing hair?

Dr. A: Exactly. In fact, we can measure thousands of molecular signatures within each growth ring. If you give me one centimeter of hair containing about 1,000 growth rings, and we measure about 10,000 molecular signatures in each one, that’s roughly 10,000,000 data points from a single strand of hair.

Dr. M: 10,000,000 data points from a single strand of hair. That’s astonishing.

Dr. A: The scale of information is enormous. And what makes it valuable is that it is time-resolved. Blood tests show you whether something is high or low at a single moment. Hair allows you to see patterns and rhythms over time. It’s similar to the way people use wearable devices like Apple Watches or Fitbits to track their activity or heart rate throughout the day. Hair analysis is somewhat like that, except it measures thousands of molecular markers inside the body rather than just a few external indicators.

Dr. M: Let me ask about something practical. When we talk about environmental toxins—heavy metals, pesticides, microplastics—are those things that can also be detected in hair?

Dr. A: Yes, absolutely. Hair can capture evidence of both internal biological processes and environmental exposures. We can detect heavy metals such as lead and arsenic, pesticides, compounds from plastics like BPA and phthalates, as well as substances the body produces itself, such as hormones, lipids, and cholesterol.

Dr. M: Earlier methods of hair testing had a reputation for being unreliable. What technological changes have enabled you to extract such precise information now?

Dr. A: The challenge historically was contamination. The outer surface of hair can accumulate substances from the environment. For example, I’m a non-smoker, but if I walk through Manhattan where people are smoking, nicotine can settle on the outside of my hair. Older testing methods analyzed clumps of hair and could mistake those external contaminants for internal exposures.

To solve this, we developed a technology that opens the hair strand lengthwise, almost like opening a book. That allows us to analyze the inner core of its shaft, which reflects what was coming from the bloodstream. By removing the contaminated outer layer, we can isolate the internal molecular archive.

Dr. M: And this is done with robotics, correct?

Dr. A: Yes. Human hands can’t consistently achieve that level of precision, so we developed robotic systems that stretch the hair perfectly straight and open it lengthwise. These robots allow us to examine growth rings in extremely fine detail without damaging the molecular information within them.

Tracking Environmental Exposure After Wildfires Through Hair Analysis

Dr. M: I want to return to the wildfire example that first caught my attention. Families who had been exposed to the fires left their homes and stayed in hotels for weeks while the houses were being repaired. How did hair testing help determine what they had actually been exposed to?

Dr. A: That situation illustrates why time-based analysis is so powerful. When those families fled the fires, they understandably weren’t thinking about collecting blood samples. By the time they were tested later, their blood toxin levels had already begun to decline because blood turns over quickly. But hair preserved a record of the exposure.

When we analyzed the hair, we could see the pattern very clearly. While the families were near the fires, the toxin levels were rising. When they moved to hotels, those levels began to drop. When a parent returned briefly to clean the home, the levels rose again. The hair essentially mapped the entire exposure timeline.

Dr. M: That kind of pattern recognition seems incredibly useful for environmental medicine.

Dr. A: It really is. Blood gives you a single pixel of information. Hair gives you the entire pattern.

Dr. M: You’ve also applied this technology to studying chemical exposures in everyday life—things like BPA, phthalates, and flame retardants that many people worry about.

Dr. A: Yes. We measure dozens of these compounds. Many consumer products contain chemicals that can disrupt the endocrine system. In our research, we’ve examined exposures to phenols such as BPA, plasticizers such as phthalates, flame retardants used in furniture, and chemicals associated with nonstick cookware.

Dr. M: That raises an important question. If people discover they’ve been exposed to these chemicals, what can they realistically do to improve their health?

Dr. A: The most effective step is reducing exposure. You can’t change your genes, but you can make choices about the products you bring into your home, the food you eat, and the environments you spend time in. When people reduce those exposures, we often see improvements in markers such as oxidative stress over time.

Early Detection of Autism

Dr. M: I want to shift to another area of your work that’s getting a lot of attention—autism research. You’ve developed a biochemical test that can help rule out autism spectrum disorder using hair samples.

Dr. A: Yes. One of the biggest challenges in autism is delayed diagnosis. Autism exists at birth, but the average diagnosis occurs around five years of age. By that time, many opportunities for early intervention have already passed.

Dr. M: That delay is something clinicians struggle with all the time.

Dr. A: Exactly. We developed a test that can analyze a single strand of hair collected as early as one month after birth. By studying patterns in certain metabolic pathways—particularly those involving zinc and copper—we can identify signatures associated with autism spectrum disorder

Dr. M: And this test is extremely accurate?

Dr. A: In large studies involving families across multiple countries, we’ve shown that the test can rule out autism with more than 99 percent accuracy in the general population. The goal is to identify risk early so that interventions can begin during the critical stages of brain development.

Dr. M: That could be life-changing for many families.

Dr. A: Early therapy can dramatically improve outcomes. In some cases, children who receive early intervention may even fall below the diagnostic threshold for autism later in life.

Dr. M: Before we finish, I’d like to ask a practical question. If someone wanted to have their hair analyzed through your company, how accessible is that testing?

Dr. A: We designed the testing to be accessible. A home exposure analysis typically costs under $200, and the autism screening test costs under $500. People can request the tests through our website, and we provide support to anyone with questions about the process.

Dr. M: Dr. Arora, this has been an extraordinary conversation. I started this interview skeptical about hair analysis, and I’m leaving with a completely different perspective on how powerful this tool could be for understanding environmental exposures and human health. Thank you for having this important conversation.

Dr. A: Thank you, Dr. Mitchell. It’s been a pleasure to speak with you and your readers.

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Dean Mitchell, MD, is a board-certified allergist, immunologist, and integrative medicine specialist with over 25 years of experience. He is the founder of Mitchell Medical Group in New York City and a national leader in sublingual immunotherapy, a safer and more natural treatment for allergies. Dr. Mitchell is the author of Dr. Dean Mitchell’s Allergy and Asthma Solution, which offers an innovative, holistic approach to managing immune and allergic conditions.

A graduate of the Tel Aviv University School of Medicine, he is also the host of The Smartest Doctor in the Room podcast, where he explores cutting-edge strategies for treating chronic illness and restoring vibrant health. https://www.mitchellmedicalgroup.com

Manish Arora, PhD, is an environmental epidemiologist and exposure biologist whose research examines how environmental exposures during pregnancy and early childhood shape lifelong health. He is the Edith J Baerwald Professor and Vice Chair of Environmental Medicine and Public Health at the Icahn School of Medicine at Mount Sinai and founder of Linus Biotechnology.

His work led to an FDA Breakthrough autism biomarker detectable at birth. He is also the author of Environmental Biodynamics and received the Presidential Early Career Award for Scientists and Engineers from President Barack Obama.

Well Being Journal adapted the above transcript from the podcast The Smartest Doctor in the Room, Episode 212, “What Your Hair Can Tell You About Your Health,” hosted by Dean Mitchell, MD. Reprinted with permission from Mitchell Medicine.