Denatured alcohol is ethyl alcohol — ethanol — with an additive, usually methyl alcohol, that makes it unfit for humans to drink. The denaturing agents are chosen to be toxic, intensely bitter, or foul-smelling, so the product cannot be diverted into the drinks trade; common formulas add methanol, isopropanol, or bittering agents like denatonium. Because it cannot be drunk, denatured alcohol escapes the heavy excise duties levied on potable spirits, making it cheap for its legitimate uses: laboratory and medical disinfection, cleaning, solvents, fuel, and cosmetics manufacture. Food plants use it for sanitising where potable alcohol would be a tax absurdity. The system is a fiscal device rather than a safety one — the alcohol itself is identical to the drinkable kind, and the additives ensure it stays in the factory and out of the bottle.