Dirty cloths containing grease and oil stains are cleaned by adding detergents to water. Stains are removed because detergent :

Detergents act as surfactants (surface-active agents) that significantly reduce the surface tension of water [3]. Water naturally has high surface tension due to cohesive forces, which prevents it from effectively wetting oily surfaces [2]. Detergent molecules possess a dual nature: a hydrophilic (water-loving) head and a lipophilic (oil-loving) tail. When added to water, these molecules position themselves at the interface between water and oil, disrupting the cohesive forces and lowering the interfacial tension to nearly zero [2]. This reduction in surface tension allows the water to spread, wet the fabric, and emulsify the grease into structures called micelles [3]. By drastically reducing the tension between the immiscible liquids, the detergent enables the oil to be lifted from the cloth and suspended in the water to be washed away [1].

Sources

1. [3] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 7: Particulate Nature of Matter > Ever heard of ... > p. 111
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > Activity 4.10 > p. 75
3. [1] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 10: Light: Mirrors and Lenses > Activity 10.8: Let us explore > p. 162