The four appendages of the skin include sebaceous or oil glands, sweat or sudoriferous glands, hair, and nails. The appendages reside in the dermis and are generated in the epidermis.
Sebaceous glands produce an oily substance known as sebum. Sebum contains antibacterial properties and also functions to keep the hair and skin soft. It is connected via a duct to a hair follicle. The sweat glands produce sweat, an important component in keeping the body cool when it becomes overheated. The nervous system controls the function of the sweat glands and their ability to regulate temperature. Both hair and nails are formed from keratinized cells, or skin cells that have undergone a hardening process.