The principle of cleaning by soap is

The primary principle behind the cleaning action of soap is the reduction of surface tension. Soap molecules are surfactants, meaning they possess a dual nature with a hydrophilic (water-attracting) ionic head and a hydrophobic (water-repelling) long-chain hydrocarbon tail [3]. In water, these molecules align at the surface to lower the surface tension, which allows the water to spread more effectively and 'wet' the fabric or surface being cleaned. This reduction in surface tension enables the water to penetrate dirt and grease that it would otherwise bead off of. Furthermore, soap molecules form micelles, where the hydrophobic tails trap oily dirt in the center while the hydrophilic heads remain in contact with water, creating an emulsion that can be easily rinsed away [2]. Thus, lowering surface tension is the fundamental physical mechanism that initiates the cleaning process.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > Activity 4.10 > p. 75
2. [2] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 7: Particulate Nature of Matter > Ever heard of ... > p. 111