Sebaceous glands secrete an oily substance called sebum (tallow) that is made of fat (lipids) and the debris of dead fat-producing cells. In the glands, sebum is produced within specialized cells and is released as these cells burst. Sebum is odorless, but its bacterial breakdown can produce odors. Hyperactive sebaceous glands produce too much sebum which is the cause of oily hair or skin and is also involved in skin problems such as blemished skin and dry and itchy scalp. Therefore, an important part of treating these conditions is the reduction of the sebum production.