The pH scale measures how acidic or basic a water-based substance is, ranging from 0 to 14. A pH of 7 represents a neutral solution, like pure water. Substances below 7 are acidic (e.g., lemon juice), while those above 7 are basic, or alkaline. Understanding this framework helps analyze common household products, including dish soap.
The pH Profile of Dish Soap
Most liquid dish soaps formulated for handwashing are slightly alkaline. The pH of commercial dish detergents usually falls between 7 and 10. Brands marketed as “gentle on hands” often hover closer to neutral, with a pH between 7 and 8.
The primary cleaning agents in dish soap are surfactants, which reduce the surface tension between liquids. These surfactants and pH buffers are balanced to achieve the final pH value. A near-neutral to mildly alkaline formulation maximizes cleaning efficiency while minimizing skin irritation.
How pH Affects Cleaning Power
The slightly alkaline pH of dish soap is effective because it aids in breaking down organic materials, primarily fats and oils. Alkaline solutions are good at cutting through grease and removing oily residues. This contrasts with acidic cleaners, which are better suited for dissolving mineral deposits, rust, and limescale.
The basic environment facilitates two chemical processes: emulsification and saponification. Emulsification allows soap to act as a bridge, mixing oil (non-polar) with water (polar) so the grease can be rinsed away. Saponification is the reaction where the alkali reacts with triglycerides (fats and oils) to produce soap and glycerol, converting the grease into a water-soluble substance.
Practical Implications for Home Use
The mildly alkaline nature of dish soap has consequences for human skin health. Human skin maintains a slightly acidic surface layer, the “acid mantle,” which typically has a pH between 4.0 and 6.0. This acidic barrier helps retain moisture, supports beneficial bacteria, and inhibits pathogens.
Washing with a basic substance temporarily raises the skin’s pH. This disruption can compromise the skin’s barrier function, potentially leading to dryness, irritation, or increased susceptibility to issues like eczema. Frequent, prolonged exposure to a pH above 7 can strip the skin of its natural oils.
For household surfaces, the mild pH of handwashing dish soap makes it a safe choice for general cleaning. Highly acidic or strongly alkaline cleaners can damage materials like stone countertops or certain metals. Since most dish soap is near-neutral, it is safe for everyday use on a wide variety of kitchen surfaces without causing etching or corrosion.