A layer of skin beneath the epidermis is called the dermis. It contains both sweat glands and sebum glands. The sweat and sebum produced from the glands come up to the skin surface through narrow channels known as pores.
The innermost layer of human skin is known as the subcutaneous layer. This is where hair begins its growth. It grows out of follicle, and makes its way through the other layers. Our skin contains thousands of minute hair follicles. Each comprises a sebaceous gland, which generates an oily substance termed sebum. Along with other lipids like linoleic acid, the dead skin cells, oily sebum and sweat together accumulate on the skin’s surface. This acts as a protective shield to prevent your skin from drying out.
Often an ‘unusual’ reaction of the sebaceous glands to the male hormone testosterone may cause them to make more sebum in the skin. As a result, sudden spike in sebum production happens.
This overproduction of sebum coupled with dead skin cells tends to block hair follicles. It’s the presence of skin pigment, and not dirt that causes the characteristic ‘blackhead’ appearance. On other hand, whiteheads are more common in nature. They are likely to become inflamed since the grease and bacteria, which is accumulated, finds no escape route.