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How Interior Medicine Evaluates Products

Interior Medicine rates home products against fixed, published tier scales for each material and health function, using third-party certifications and documented evidence as reliable indicators of performance rather than brand claims or marketing language.

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 28, 2026 | Updated August 21, 2026

The Interior Medicine Method

The Interior Medicine Method rates products against consistent, published standards, applied the same way every time. Every material, filter, or finish is checked against third-party certifications, data, and documented evidence, not against how the product is marketed or whether it feels healthy or effective.

I do this because marketing is tricky, and most top-ten non-toxic round-ups don't add clarity. They mostly repeat brand claims, sometimes with personal opinion layered on top. But if you measure everything the same way, the truth emerges on its own: you can see, side by side, how healthy or effective a product really is compared to the next one.

I think of it as x-ray vision. Marketing and casual round-ups show you the surface level of a product and what it claims to do. The Interior Medicine Method looks deeper, at what a product is actually made of and what the evidence says about it, so what you see is it for what it really is.

In short: the Interior Medicine Method evaluates products to find what is true, not to offer an opinion, perpetuate wellness claims, or restate marketing as fact.

Methodology Overview

The Interior Medicine Method uses two kinds of scales.

Material Health Scales rate what a product is made of.
Health Function Scales rate how well a product performs the specific health job it exists to do.

Material Health Scale

See the scales in more detail here →

⟶ scroll to see all tiers

Material	Healthiest	Healthy	OK	Use Caution	Harmful
Fabric	Certified organic natural fibers (GOTS)	Natural fibers with whole-product certification (OEKO-TEX 100)	Uncertified natural fibers, or certified synthetic/semi-synthetic	Uncertified synthetic or semi-synthetic fibers	Known harmful chemistry (PVC, PFAS, flame retardants)
Foam	Certified organic latex (GOLS)	Natural rubber latex with whole-product certification (C2C, ecoINSTITUT)	Synthetic foam with some certification, or uncertified natural latex	Synthetic foam with minimal or no certification	Known harmful chemistry (PVC/vinyl foam)
Wood	Solid wood, unfinished or natural finishes only	Solid or no-added-formaldehyde wood with whole-product certification	Solid or engineered wood, low-VOC finish, uncertified	Standard wood with conventional surface treatments	Known harmful chemistry (melamine, thermofoil, PVC laminate)
Adhesive	No adhesive, or naturally-derived	Water-based synthetic adhesive with whole-product certification	Water-based synthetic adhesive, uncertified, or fully-cured epoxy	Solvent-based adhesive, uncertified	Known harmful chemistry (solvent-based + PFAS/biocides)
Metal	Bare metal, no chemical coating	Stable applied chemistry, ideally certified	Likely-safe coating resting on brand claims, not verified	Conventional coating, untested/undisclosed, or untraceable origin	PFAS non-stick, confirmed lead exposure paths
Ceramic	Third-party leach-tested, lead/cadmium below Prop 65	Modern ceramic under Prop 65 / EU compliance pressure	Brand-claimed lead/cadmium-free, no third-party testing	No testing, no traceable origin	Documented lead, cadmium, or heavy metals
Glass	Plain modern glass, no surface coatings	Modern glass with stable mineral additives (lead-free crystal)	— no OK / Use Caution tier for this material —		Lead and heavy metals (vintage lead crystal)
Plastic	No plastic	Plastic with third-party migration certification	No Prop 65 warning, but no migration certification	No certification, no Prop 65 status, no disclosure	Active Prop 65 warning

Health Function Scale

See the scales in more detail here →

Tier	Definition
Highest	Fully performs the health function with no meaningful compromise. The best available option for the job this product exists to do.
High	Performs the health function well, with a minor limitation or tradeoff that keeps it just short of the best available.
Moderate	Partially performs the health function. Workable for many people, but with a real gap compared to higher-rated options.
Low	Performs the health function poorly. Falls short of what the product is meant to deliver for most uses.
Lowest	Does not meaningfully perform the health function. Little to no benefit for the job this product is meant to do.

More About How Material-Based Products Are Evaluated

Furniture, Bedding, Cribs, Mattresses, Cookware, Rugs, Decor, Kitchenware and More

These products are evaluated based on what they’re made of. They’re items that contribute to the surrounding air and dust in your home, or that you come into physical contact with.

Furniture doesn’t have ingredients lists, so third party certifications exclusing harmful ingredients are used as the most reliable proxy. You can read about this process in detail here: How to Know What’s in a Product Without an Ingredient List.

Materials in this category have third-party certifications that test for hazards, which makes layer-by-layer evaluation possible. This includes international testing bodies like GOTS, OEKO-TEX, GreenGuard, and others. Each product is broken down into its material components, then each material (wood, foam, fabric, glue, metal, ceramic, glass) is evaluated separately against the certifications relevant to it. Full certification logic and detailed tier criteria for each material are in the Material Health Guides.

Every rating is relative. Nothing is perfectly non-toxic, and nothing is 100% toxic. The relevant question is not whether the finished product is "non-toxic" as a whole (no single certification evaluates a finished couch), but where the materials its made of sit on a spectrum from healthiest to harmful, defined by the certifications and evidence available at this moment. The spectrum itself shifts over time: materials standard a decade ago have been reformulated or phased out, new certifications appear, existing ones become more rigorous over time (or watered down), and the research about how materials affect our health changes, too. A rating on this site is a snapshot, not a permanent verdict, and the goal of the methodology is to make sure each one is consistent and fact-based.

More About How Products Are Rated with the Health Function Scale

Air Purifiers, Water Filters, Waterproof Items, and More

Some products are also rated on their health function. This is because their effectiveness as a tool for a healthier home is more important than what its made of. For example, an air purifier’s primary job is to remove harmful particles and VOCs from your home. A shower curtain should be waterproof enough that your bathroom doesn’t get damp or grow mold. A radon detector should be effective at detecting radon. This matters more than what they are made of.

When a Product is Rated on Both Scales

Blackout Curtains, Shower Curtains, Mattress Protectors, and Others

When a product is rated on both scales, the two ratings are independent and can point in different directions. An organic cotton blackout curtain may earn the highest material rating while landing lower on health function, because natural fibers can't achieve total blackout on their own. A synthetic curtain may be the reverse. Showing both, rather than collapsing them into a single verdict, is what lets you weigh the tradeoff against your own priorities.

Limits of This Methodology

The methodology above reflects the most rigorous approach currently possible given available evidence, certifications, and solo-operator resources. Not every product category has a completed rating yet. New material and health function scales are added as they're built out. The limits noted here are documented so they can be addressed as the field develops, as new certifications become available, and as the site's capacity expands. Updates will be made as warranted.

Certification reliance is partial coverage, not full disclosure. Where a certification tests for a defined set of substances, the evaluation is robust within that set. Substances outside the certification's scope remain unknowns, regardless of whether the product is otherwise well-certified. A GOTS-certified cotton fabric has been evaluated against GOTS criteria, not against every substance that could theoretically be present. This is the best available proxy for material composition disclosure, but it is a proxy.
Material-layer evaluation does not capture interactions between layers. The methodology rates each material layer separately and assigns the product's overall rating to its weakest layer. This is a reasonable simplification but does not account for chemical interactions across layers, the way certain finishes alter the off-gassing behavior of underlying materials, or cumulative effects from multiple low-rated layers.
The rating tier system is ordinal, not quantitative. Healthiest, Healthy, OK, Use Caution, and Harmful are relative positions on a scale, not measured exposure values. Two products in the same tier are not necessarily equivalent in actual exposure delivery, and the boundaries between tiers reflect judgment about which certifications and material characteristics warrant which classification rather than measured thresholds.
The methodology is documented but not externally audited. No third party has reviewed the rating logic for consistency, the database for completeness, or the per-category criteria for methodological soundness. This is standard for solo-operated resources but is a limit relative to formally peer-reviewed or institutionally audited methodologies.

A Note on “Non-Toxic” Terminology

The words non-toxic, chemical-free, toxin, and toxic appear throughout Interior Medicine despite being scientifically imprecise. No agreed-upon definition of non-toxic exists. Everything is made of chemicals, including water, so nothing is truly chemical-free. Toxin refers specifically to a natural poison or venom, while toxicant is the accurate term for synthetic chemicals with negative health effects. A substance being toxic at some dose does not mean it presents a health risk at the doses encountered in homes.

These terms are used anyway, for practical reasons. They are the most culturally recognized and searchable language for what people are looking for when they research healthier home products. Using technically correct terminology that no one searches for would make the information unfindable. Non-toxic is treated here as shorthand for a complicated problem, not as a literal claim. The terminology will be updated when the cultural language shifts.