Question

why do some adolescents get acne on their face

Answer 1

The culprit behind acne on the face of adolescents is Sebaceous glands and it's secretion sebum.
Sebaceous glands are present in all mammals, especially on face and scalps, these secrete a waxy fluid named sebum to waterproof and moisturize the skin.
During adolescence secretion from these glands increase, an excess amount of sebum blocks the sebaceous ducts and causes inflammation and thus acne.