The main ingredients in modern dry-erase markers include ethanol or isopropanol, pigments, an oily surfactant or co-solvent, and a polymer or resin. Originally, dry-erase markers used solvents that contained benzene.
The modern dry-erase marker has four basic ingredients. The carrier or solvent, typically ethanol or isopropanol, limits smearing and aids in drying. The coloring is created by pigments. A release agent, taking the form of an oily surfactant or co-solvent, prevents the ink from setting. Polymers or resin are added to help the ink spread evenly and not bead up. They also help the ink stay cohesive and stick to itself and not to the board surface.
The first dry-erase markers used benzene as their solvent. In the early 19th and 20th centuries, benzene was valued for its pleasant scent and degreasing attributes. It was used as both a men's aftershave, an industrial solvent and even as an additive to decaffeinated coffee. Eventually the toxicity of the compound and its carcinogenic nature were discovered. By the late 20th century, benzene had been almost completely replaced by other chemicals in most consumer applications, including dry-erase markers.
Modern dry-erase inks now use alcohol-based solvents to carry their ink. This change came in response to complaints about the marker's high toxicity and the strong odor created by the benzene solvents. Consequently most modern dry erase markers are now labeled "non-toxic."