Skin cells are the basic building blocks of the skin, which is the largest organ of the human body. These cells form a protective barrier that helps to keep out harmful substances, regulate temperature, and prevent water loss. The outermost layer of skin, known as the epidermis, is primarily made up of keratinocytes, which produce a protein called keratin that strengthens the skin. There are several types of skin cells, including melanocytes, which produce the pigment melanin that gives skin its color, and Langerhans cells, which play a role in the immune response. Skin cells continuously regenerate, with new cells forming at the base of the epidermis and gradually moving to the surface, where they eventually shed off.