CBSE Class 10 Answered

Dear student,

Soap cleanses the skin, because it is a surfactant composed of hydrophobic fragments (water-insoluble) and hydrophilic fragments (water-soluble), which are at the same time lipophobic (fats-insoluble). According to the rule that ''like dissolves like'' a hydrophile fragment dissolves in water and a lipophobic binds with fat and dirt particles. Oil-in-water (O/W) type emulsion emerges, which prevents dirt from accumulating on the skin surface and facilitates rinsing of soap with water.

However, ordinary soaps are alkaline – have pH of about 9 and thus they can damage the skin's acidic barrier (about 5,5 pH), disturb the bacterial flora balance. In result, it increases the risk of the penetration of the skin by microorganisms or allergens. Breaking the continuity of the lipid coat also increase the skin's dehydration. After the soap is rinsed away, the skin remains alkaline with pH of 7-8. It takes at least 30 minutes for the lipid coat to rebuild. Sometimes this process takes even 3 hours. Thus,over-use of ordinary soaps might cause irritation to skin

In simpler words, the soaps  solubilise fats and oils. The skin requires some of the fats and oils secreted by the body to keep it in a reasonable condition. Over use of soaps and detergents removes too much of these oils with the result that irritation happens.