Many yarn manufacturers make mothproof wool, which is chemically treated to repel or kill moths that come in contact with it. This sounds like a great idea to some knitters, while others are a little nervous at the prospect of having chemicals they don't know much about so close to their skin.
I asked Robert Wells of Brown Sheep Company about the process that is used to mothproof wool.
He told me that the chemical used to mothproof wool, Mitin FF, is added to the yarn in the dye bath at the same time as any coloring that is being added to the yarn. The mothproofing agent adheres to the yarn in a similar way as the dye does.
This means that like dye, the chemical will not rub off or wash off in normal cleaning or dry cleaning.
Mitin FF is a pesticide that works by killing the moth larvae when the ingest and digest the wool protein, which means if you do ever get moths in your stash, they won't be able to do a lot of damage.
But if the chemical kills moths, what can it do to humans? Wells said Mitin FF is relatively harmless if not ingested, and the federal government agrees. Mitin FF has been used as a pesticide in the United States since 1948 and is used exclusively by the textile industry for mothproofing wool. Laboratory tests have found the chemical to be "low to moderately toxic" and to have "low mammalian toxicity."
While there's no danger from using mothproofed wool, some people prefer not to use yarn with extra chemicals. For those people, a whole new world of organic wools and cottons are coming to the marketplace, allowing you to create without the chemicals.