Curiosities: What’s the difference between dishwasher detergent, laundry detergent and dish soap? Why aren’t they interchangeable?

July 26, 2010

All detergents — whether intended for hands, hair, clothes or dishes — work on the same principles: Break up oils and dirt and wash them away. However, different products are formulated for specific conditions and are not interchangeable.

The main differences are in the pH, presence or absence of bleach, and the types of surfactants — long molecules that are water-loving at one end and oil-loving at the other. “Surfactants are active ingredients we put in cleaning products that bridge the gap between water and greasy dirt and help wash it away,” says Allen Clauss, a UW-Madison chemistry lecturer who previously worked at consumer products company Procter & Gamble.

Automatic dishwasher detergents use a brute force approach that is effective but far too harsh for skin, breaking down stains and food with high pH and chlorine bleach. “It’s a great way to clean your dishes, but it’s not something you want to put your hands into,” Clauss says. Detergents for hand dishwashing do not contain bleach and use blends of surfactants that are mild to skin and work near neutral pH.

Laundry products are somewhere in between — tougher than hand dishwashing products but gentle enough for fabrics and dyes. Traditional powdered versions are closer to automatic dishwasher detergents and use higher pH to clean, while the newer liquid detergents are closer to neutral pH and rely more on surfactants that are less susceptible to water hardness, enzymes to break down proteins, starches and fats, and water-soluble polymers to help disperse dirt and oils.