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What “Non-Toxic” Actually Means: A Course

Dr. Meg Christensen is the physician founder of Interior Medicine, a non-toxic home resource built on her background in medicine, biochemistry, epidemiology, and clinical research

Published March 1, 2026 | Updated June 4, 2026

Welcome to What "Non-Toxic" Actually Means, a free course on how to read product claims and navigate healthier materials more clearly. Working through the parts in order makes the most sense, but you can jump around if you want.

The Intro takes ~8 min to read

Welcome!

How the Course Works

The course is set up as two volumes. The first half goes deep on background: why there's so much conflicting non-toxic advice, toxicology basics, how to read a research study, why people perceive the same risk so differently. This foundation matters for the second half, but it's not where everyone needs to start.

The second half, starting at Part 6, shifts from background philosophy to the practical work of evaluating a product: how to use certifications and chemical behavior, and which parts of the toxicology framework are yours to decide rather than mine. It's what I do to evaluate any product, and I'm showing the full complexity. If it feels too heavy, the Second Opinion Product Checker at the end is the fast way through: it walks you through a real product start to finish, and you can circle back to the parts you're most curious about afterward.

The whole thing takes 2½–3 hours, and you can work through it at your own pace. Jump around if you'd like, though if you have questions, the answer might be in an earlier part.

Browse the curriculum and read more about why I wrote this course below, or get started with Part 1 now ➜

What “Non-Toxic” Actually Means: A Course by Interior Medicine
Course Curriculum

        
        10 parts
      

        
        Self-paced
      

        
        Free
      
Volume 1
Why Nobody Agrees on What “Non-Toxic” Means
01
Why “Non-Toxic” Information Is So Confusing Right Now
Every institution has a different top-ten-to-avoid list, brands claim non-toxic but end up in court, and the doctors and influencers you'd trust to sort it out contradict each other. Why it's all so confusing, with a map to get out of the mess.
02
Hazard vs Risk: The 6-Step Toxicology Framework
Why EWG ratings, Prop 65 warnings, and “sunscreen in blood” headlines all measure something other than toxicity. The six-step toxicology framework that clarifies what they are instead.
03
How to Read a Toxicity Study in 4 Steps
Four steps to reach for when you get that “wait, is this real?” feeling about a research claim. Plus why environmental health research so often contradicts itself.
04
Why “Is It Non-Toxic?” Has No Clean Answer
Just how complex a single product really is, why a tidy yes-or-no on “non-toxic” doesn't exist, and why that's freeing rather than discouraging.
05
Why Smart People Disagree About the Same Facts
Worldview and identity quietly shape how we perceive danger, and understanding that is both illuminating and useful. A personality quiz on EMFs that reveals how you interpret risk, and why the person who disagrees with you isn't being unreasonable.
Volume 2
The Interior Medicine Method
06
What Household Chemicals Should I Avoid?
The 70 substances that show up across scientific, advocacy, and wellness sources. Hazard is the starting point, not the endpoint, for the rest of this course.
07
Can Toxins in Products Actually Reach You?
A hazard on a list is one thing. Whether it becomes an exposure that reaches your lungs, skin, or bloodstream is another. How to tell the difference.
08
Detox Your Home: 5 Strategies For 70 Hazards
How to reduce the chance that anything hazardous in your home reaches a meaningful dose in your body.
09
What Does “Non-Toxic” Mean?
How susceptibility, risk, and relativity shape the actual answer to the question this course started with.
10
Second Opinion: A Non-Toxic Home Product Checker
The six-step framework turned into a tool you can use. Parts 6 through 9 at working speed.

Why This Course Exists

I wrote this course because figuring out what's truly non-toxic can be so confusing.

Every major institution has a different list of the top hazards. Brands that market themselves as non-toxic keep getting caught in lawsuits. Everything has a Prop 65 sticker on it. Research appears to contradict itself, and regulatory positions on things like formaldehyde and PFAS keep shifting. Even ingredients that seem completely benign — aloe vera, chamomile — have been flagged by major organizations, which raises more questions than it answers about how to interpret those flags in the first place.

What You’ll Learn

This course is about the why: why the same chemical gets a hazard rating from one institution and a safe rating from another, why you see research papers that say exact opposite things about the same toxicant, why the wellness influencer your friend follows sounds crazy to you and like the truth to her, and why we're in such a confusing moment in the first place.

There are very satisfying explanations for each of these things, and I hope this course feels like a series of aha! moments to you. Each section takes the bird's-eye view to see the complexity for what it is, and looks beyond where we usually look for answers. The course pulls from history, toxicology, research methodology, psychology, sociology, neuroscience, chemical behavior, and risk interpretation.

We go into the science and certainty as much as we go into relationships and navigating uncertainty. The course takes the bird's-eye view of why this whole conversation is so confusing, and it dives into the underlying mechanics so the patterns actually make sense.

It's challenging! These topics are complicated, but if you’re here, you’re probably looking for a deeper explanation. I recommend starting when you can get settled in.

It's not meant to be prescriptive or proprietary. There are references at the bottom of every page so you can see the studies behind what I write, rather than taking my word for it, and follow up on anything you want to look at more closely. In the second half, I use the word Method, but not to suggest a secret system you have to follow. It's just the actual steps I use, which you can take apart and adapt for your life.

Get started with Part 1 now ➜