What is the substance that makes up the water barrier of the skin?

The water barrier of the skin is primarily composed of keratin and lipids, which play vital roles in maintaining the skin's hydration and protective functions. Keratin, a type of fibrous protein, is abundant in the outer layers of the skin, particularly in the stratum corneum. It helps create a tough, protective layer that minimizes water loss and safeguards underlying tissues.

Lipids, which include fatty acids, ceramides, and cholesterol, are interspersed among the keratinocytes in the stratum corneum. They fill the spaces between the cells and contribute to forming a hydrophobic barrier that prevents transepidermal water loss. This lipid matrix is crucial in keeping the skin moisturized and also helps protect against environmental damage and pathogens.

Understanding the composition of the skin's water barrier highlights the importance of both keratin and lipids in preserving skin integrity and function. Other options like collagen and elastin are important for skin structure and elasticity but do not directly contribute to the water barrier. Hyaluronic acid is primarily involved in hydration and moisture retention within tissues but is not a major component of the skin's outer protective barrier.