Surfactant

Surfactants (surface-active agents) are amphiphilic molecules — they have a water-loving (hydrophilic) head and an oil-loving (lipophilic) tail. When applied to skin with water, their tails surround and encapsulate oil, sebum, and particulate dirt into micelles, which are then rinsed away. In cosmetics they serve as cleansing agents, emulsifying agents (stabilising oil-in-water or water-in-oil emulsions), and foam boosters. Harshness varies significantly: sodium lauryl sulfate (SLS) is a strong anionic surfactant that can disrupt the skin barrier; gentler options like cocamidopropyl betaine and sodium cocoyl isethionate are preferred for sensitive skin.

• pH A scale from 0 to 14 measuring how acidic or alkaline a solution is; 7 is neutral.
• Emollient An ingredient that softens and smooths skin by filling gaps between skin cells.