Final answer:
A mass of keratinized cells and harder sebum is a blackhead, which is formed when sebum and dead skin cells accumulate in the hair follicles and oxidize. Proper cleansing and exfoliation are necessary to remove blackheads and prevent future blockages.
Step-by-step explanation:
A mass of keratinized cells and harder sebum refers to the formation of a comedo, which is commonly known as a blackhead. Blackheads occur when sebum and dead skin cells accumulate in the hair follicles and oxidize, resulting in a dark appearance. The excess production of sebum can be caused by hormonal changes, improper skin care, or certain medications. Removing blackheads involves gentle cleansing and exfoliation to unclog the pores and prevent future blockages.