Sebum
Sebum plays a part in the defense mechanism of the body by acting as a barrier to microorganism attack. Sebum produced by sebaceous glands travels via the hair follicle and above the upper layer of the skin. Sebum also carries dead skin cells and bacteria inside the hair follicle. Excessive sebum secretion modulated by hormonal imbalance can cause these dead skin cells, bacteria and sebum turn into a sticky substance that clogs the opening of the hair follicle.