Acne alias jerawat

Acne begins when the pores in the skin become clogged and can no longer drain sebum (an oil made by the sebaceous glands that protects and moisturizes the skin.) The sebum build-up causes the surrounding hair follicle to swell

Hair follicles swollen with sebum are called comedones. If the sebum stays beneath the skin, the comedones produce white bumps called whiteheads. If the sebum reaches the surface of the skin, the comedones produce darkened bumps called blackheads. This black discoloration is due to sebum darkening when it is exposed to air. It is not due to dirt. Both whiteheads and blackheads may stay in the skin for a long time.
Bacteria called Propionibacterium acnes (P. acnes) that normally live on the top of the skin can enter the clogged pores and infect the sebum. This causes the skin to become swollen, red, and painful.

Infected sebaceous glands may burst, releasing sebum and bacteria into the surrounding skin, creating additional inflammation. In severe cases, larger nodules and cysts may form in the deeper layers of the skin