Sebum is a natural oil produced by glands in hair follicles that keeps the skin moist and forms a barrier to protect the skin from damage. Sebum is produced by sebaceous glands that are found all over the surface of the body, except for the palms of the hands and the soles of the feet. Most of the sebaceous glands connect to hair follicles. Sebum helps to protect the scalp and hair, keeping them healthy and moisturized. It forms a barrier on the surface of the skin to protect it from the elements and oxidative damage, and it travels down the hair shaft to protect each hair strand. Sebum also helps to protect from bacterial infection by forming a barrier to keep most disease-causing microbes out. However, when sebum builds up, it can cause problems. A build-up of sebum can make the hair look greasy, dull, and oily rather than looking healthy, shiny, and voluminous. Sebum accumulation on the scalp can cause irritation, redness, and inflammation of the hair follicles, leading to flakiness, irritation, or swelling of the hair follicle.