Abarrier to pathogens is provided by a. melanin. b. collagen. c. sebum. d. keratin.

Answer;

Keratin

Explanation;The skin contains the protein keratin, which resists physical entry into cells. Keratin helps to adhere cells to each other and to form a protective layer on the outside of the skin. In epithelial cells, keratin proteins inside the cell attach to proteins called desmosomes on the surface.Keratin makes our skin tough and provides us with much-needed protection from microorganisms, physical harm, and chemical irritation.