The hard white particles inside the pimples are considered to be a mixture of keratin plugs and sebum.
Pimples are generally referred to as acne, and the cause of its development is mainly related to keratinization of the hair follicle orifices, androgen levels, and increased sebum production. During puberty, the sebaceous glands produce more sebum due to elevated androgen levels, and the sebum mixes with shed epidermal tissues to form a sludge-like substance that can clog pores leading to acne.
Acne has also been linked to the over proliferation of Propionibacterium, a bacterial overgrowth that stimulates an inflammatory response in and around the hair follicles, causing the mixture to collect.
In most cases, acne will subside on its own as the body’s hormone levels gradually stabilize with age, but if acne is more severe, it should be treated actively. Usually, you should pay attention to keeping your skin clean and hygienic, choose mild skin cleansers, avoid spicy and stimulating foods in your diet, and make sure that you get enough sleep to avoid too much mental stress.