Ethoxydiglycol Back in the '50s, home hair dyes were laced with toxic chemicals that turned a simple touch-up into a haz-mat operation. Luckily, dye makers found substitutes like EDG, a fume- free organic solvent that keeps the ingredients in a thin, pourable consistency.

Oleyl Alcohol, Vegetable Fatty Acid That thin, pourable consistency would be problematic during application. Mixing the base with the separate bottle of "color developer" causes these two fatty organic thickeners to kick in, making the product cling to your hair like shampoo.

Ethanolamine In last month's episode of What's Inside, this ingredient starred as a solvent in Easy-Off oven cleaner. Here it's an alkalizer that boosts the pH toward bleachlike levels and swells the hair's outer layer so the color can penetrate more fully.

Erythorbic Acid If you take ascorbic acid — aka vitamin C — and rearrange the atoms just so (isomerization!), you get erythorbic acid. It's a cheaper antioxidant that protects the dye from sun and oxygen damage.

Trisodium EDTA With its ability to bind heavy metals, EDTA is used to clean up after radioactive spills. That same talent is enlisted here to suck up copper in tap water, which might otherwise react with the product to create damaging radicals. Dyed hair is messed up enough already.

Polyquaterium-22 Sounds like a comic- book invention, but this common polymer coats each strand, smoothing the shaft's outer layer and improving lubricity — a fancy way of saying it's a hair conditioner.

p-Aminophenol, p-Phenylenediamine These so-called intermediates react inside the hair fiber to produce the appropriate color when oxidized. This combination turns dark brown. Other chemicals (or different proportions of these) can make any shade — from Sandy Blond to Jet Black.

Resorcinol Is there anything this stuff can't do? It's used as a chemical skin peel, a biological glue for aortic surgery, a sunscreen, a treatment for whooping cough, and — when mixed with the right acids — a TNT-like explosive. In Just for Men, it's a coupler, an additive that reacts with the oxidized intermediates to dial in the target color.

Hydrogen Peroxide When combined with the other ingredients, this ubiquitous denizen of the medicine cabinet provides a superabundance of highly reactive oxygen, which turns those intermediates and couplers into luxurious dark coloring that will surely fool everyone into thinking that this is your natural look.