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What “Non-Toxic” Actually Means: A Free Course

This free course explains why "non-toxic" claims are so inconsistent across brands, institutions, and research, walking through the underlying reasons rather than just listing which chemicals to avoid. It draws on toxicology, research methodology, psychology, and risk interpretation to explain why the same chemical gets flagged as hazardous by one organization or person and cleared as safe by another. The material builds through a series of parts meant to be read in order, though each section stands on its own if you want to jump to a specific topic. Every page includes references to the underlying research, so claims can be checked against primary sources rather than taken at face value.

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

Published May 11, 2026 | Updated September 1, 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

This is free and always available. The entire course takes most people around 2–3 hours to read, 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.

Read more about why I wrote this course below, or get started with Part 1 now ➜

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 ➜