Dirt can be perceived as three broad categories: organic, inorganic and a combination. Organic dirt covers a broad range and include food soils such as fat, grease, protein, and carbohydrate, living matter such as mold, yeast and bacteria and petroleum soils such as motor oil, axle grease and cutting oils. Most of the time organic soils are best removed using alkaline cleaners or solvents.
Inorganic soils include rust, scale, hard water deposits and minerals such as sand, silt and clay. Oftentimes acids are used to remove inorganic deposits such as rust and scale. Minerals are often cleaned with general purpose cleaners.
Combination soils often present the toughest challenge for a cleaner since the soil contains both organic and inorganic components. Most combination soils are removed with a very concentrated, highly built cleaner that also contains solvent.
A surfactant is the most important part of any cleaning agent. In general, they are chemicals that, when dissolved in water or another solvent, orient themselves at the interface (boundary) between the liquid and a solid (the dirt we are removing), and modify the properties of the interface.