Denatured alcohol is ethanol (ethyl alcohol) made unfit for human consumption by adding one or more chemicals (denaturants) to it. Denaturing refers to removing a property from the alcohol (being able to drink it), not to chemically altering or decomposing it, so denatured alcohol contains ordinary ethyl alcohol.
Why Is Alcohol Denatured?
Why take a pure product and make it toxic? Basically, it's because alcohol is regulated and taxed by many governments. Pure alcohol, if it was used in household products, would offer a much less expensive and readily available source of ethanol for drinking. If alcohol wasn't denatured, people would drink it.
What Denatured Alcohol Looks Like
In some countries, denatured alcohol must be colored blue or purple using an aniline dye, in order to distinguish it from consumption-grade ethanol. In the United States, for example, denatured alcohol need not be colored, so you can't tell whether alcohol is pure or not simply by looking at it.
What Happens If You Drink Denatured Alcohol?
Short answer: nothing good! In addition to the effects of the alcohol, you'd experience effects from the other chemicals in the mixture. The exact nature of the effects depends on the denaturing agent. If methanol is the agent, possible effects include nervous system and other organ damage, increased risk of cancer, and possibly death.
Other denaturing agents carry risks, plus many products also contain perfumes and dyes not intended for human consumption. Some of these toxic compounds can be removed by distilling the alcohol, but others have boiling points close enough to ethanol that it's unlikely an inexperienced distiller could remove them to the point where the product would be safe for human consumption. However, the distillation of a fragrance-free, dye-free product might be a viable option if alcohol is to be used in laboratory situations.
Denatured Alcohol Chemical Composition
There are hundreds of ways ethanol is denatured. Denatured alcohol that is intended for use as a fuel or solvent typically contains 5% or more methanol. Methanol is flammable and has a boiling point close to that of ethanol. Methanol is absorbed through the skin and is highly toxic, so you really shouldn't use denatured alcohol for making perfume or bath products.
Examples of Products Containing Denatured Alcohol
You'll find denatured alcohol in reagent alcohol for use in labs, hand sanitizer, rubbing alcohol, and fuel for alcohol lamps. It's also found in cosmetics and other personal care products.
Denatured Alcohol for Cosmetics and Labs
Denatured alcohol for use in cosmetics often contains water and a bittering agent (Bitrex or Aversion which are denatonium benzoate or denatonium saccharide), but other chemicals are sometimes used. Other common additives include (but are not limited to) isopropanol, methyl ethyl ketone, methyl isobutyl ketone, pyridine, benzene, diethyl phthalate, and naphtha.
Now that you know about denatured alcohol, you may be interested in learning about the ingredients in rubbing alcohol or how you can purify alcohol yourself using the simple process of distillation.