Cosmetics are integral to daily routines worldwide. Legally defined as substances intended for external human contact, the term encompasses a vast range of products.
Shampoos and soaps cleanse via surfactants, molecules with fat-soluble (lipophilic) and water-soluble (hydrophilic) properties. The lipophilic end binds to oil and dirt, allowing the water-soluble end to wash them away. Dish and laundry detergents utilize similar principles but contain harsher ingredients unsuitable for skin and hair, potentially causing irritation.
Lipstick, another common cosmetic, blends waxes (like beeswax) with non-volatile oils (like castor oil) and water. This combination creates a water-insoluble substance that spreads smoothly on lips. Its lipophilic nature prevents dissolution from saliva or drink residue. Some lipsticks employ dyes that react with skin amino acids, appearing blue or green in the container but transforming to red upon application.
Dry skin arises when surface water loss exceeds moisture absorption from underlying cells. Moisturizers combat this by preventing further water loss (occlusion) and adding humectants, which enhance the skin’s hydrophilic properties. Humectant moisturizers, containing ingredients like alpha hydroxy acids or glycerine, hydrate the skin’s surface. Occlusive moisturizers create a waterproof barrier, reducing moisture loss and enabling the body’s natural rehydration processes.