Final answer:
The main reason for a pimple is a combination of sebum overproduction, hormonal changes, the bacteria Propionibacterium acnes, and skin inflammation.
Step-by-step explanation:
The main reason for the presence of a pimple is multifactorial, involving increased production of sebum, increased levels of hormones during puberty, the colonization and infection by Propionibacterium acnes, and an inflammatory response to these bacteria within the skin. When androgens stimulate the sebaceous glands to produce excess sebum, it can combine with dead skin cells to block hair follicles, forming a plug that may appear as a whitehead or blackhead. This environment is ideal for the proliferation of Propionibacterium acnes, which leads to infection and the resulting inflammation we recognize as acne.
Acne is caused by clogged, sebum-filled pores that provide a perfect environment for the growth of bacteria. The bacteria cause infection, and the immune system responds with inflammation, leading to the formation of a pimple.