Take two bolts of fabric. Both began as wood pulp. Both were dissolved into a syrup and pushed through a showerhead of tiny holes to become thread. Both drape beautifully and feel cool on skin. On the Toxome Score, one earns an 88 for wearer health and the other earns a 64.
Twenty-four points is the widest gap inside a single fiber family that we score. It has nothing to do with the tree.
Lyocell is not a kind of viscose
Worth clearing up first, because the internet muddles it constantly. Viscose, rayon, and modal are all made by variations of the viscose process. Lyocell is made by a different process entirely. It belongs to the same broad category, manmade cellulosics, in the same way a bicycle and a motorcycle are both vehicles.
So when a tag says viscose or rayon, you are looking at the older chemistry. When it says lyocell, and especially TENCEL Lyocell, you are looking at the replacement that was invented to fix it.
The solvent is the whole story
The viscose process dissolves wood using caustic soda and carbon disulfide. That second chemical is the problem. It is a solvent that damages the nervous systems of people exposed to it over time, and in mills that run cheaply it leaves through the air and the water. The Changing Markets Foundation traced that pollution through the supply chain and found rivers running discolored beside the factories.
Lyocell dissolves the same wood using NMMO, a solvent that is not classified as toxic, inside a closed loop. Closed loop is a plain idea wearing an industrial name: the mill captures what it uses and puts it back in, rather than letting it out. Measured recovery runs above 99 percent, documented in the journal Fibers.
Same feedstock. Same finished cellulose. One process poisons a river and one process reuses its own bathwater.
Viscose is not dirty because it comes from a tree. It is dirty because of what happens to the tree.
What this means for the fiber against your skin
We will not overstate this, because overstating it is how the subject gets silly.
The thread that ends up in your shirt is cellulose either way, the same plant material as cotton. Carbon disulfide is spent during manufacturing. You are not wearing a reservoir of it. Viscose scoring 64 rather than 20 reflects exactly that: it is a middling fiber for the wearer, not a hazardous one.
What the lower score reflects is uncertainty and harm you cannot see from the fitting room. Generic viscose tells you nothing about which mill made it, how much was recovered, or what was left in the fiber. It also tends to arrive with heavier dye and easy-care finishing, and those finishes can release formaldehyde, which irritates skin and is linked to cancer. Lyocell's closed loop and traceable supply chain remove most of that guesswork. You are buying certainty as much as you are buying fiber.
There is a forest layer to this too. Because both fibers eat wood pulp, demand pulls on trees, and Canopy has shown that some of that pulp has come from ancient and endangered forests instead of managed plantations. Canopy's Hot Button Report ranks producers on exactly this, and the better mills now source certified wood.
The version of viscose that scores like lyocell
Viscose is not stuck at 64. Where a producer discloses a closed-loop process and the certification to back it, the same fiber climbs into the high eighties on our scale. LENZING ECOVERO is the clearest example, a certified viscose with far lower emissions and traceable pulp.
Which is the real lesson of this comparison. The fiber name sets a starting point. The process sets the score.
What it means for your closet
If you are choosing between two pieces and one says lyocell, take the lyocell. It is smoother, stronger when wet, better at moving moisture off your skin, and it comes with a supply chain you can name.
If you love a piece that says viscose or rayon, you do not need to put it back. Look for a named process instead: TENCEL, ECOVERO, or a brand that will tell you where its pulp comes from. Then check the finished garment for OEKO-TEX STANDARD 100, which tests for formaldehyde and harmful dyes on the thing you will actually wear. Skip anything sold as wrinkle-free or no-iron, whatever the fiber, and wash it before the first wear.
Nobody tells you any of this at the register. The tag lists a fiber and stops, as though the word alone settles the question, when the mill behind it is doing most of the work. Learning to read the difference takes about a minute, and after that you can never quite unsee it.
