Pimples form when tiny holes in the skin, called hair follicles or pores, become clogged. Here is how the process works:

• The sebaceous glands, located in the dermis layer of the skin and connected to hair follicles, produce an oily substance called sebum. Sebum's role is to keep the skin moisturized and protected.
• Sometimes these glands produce excess sebum. This excess oil mixes with dead skin cells that are naturally shed and can form a plug in the hair follicle.
• When the follicle or pore is blocked by this combination of sebum and dead skin cells, it traps bacteria that normally live harmlessly on the skin, especially Cutibacterium acnes (C. acnes).
• The trapped bacteria multiply, causing inflammation and infection inside the follicle.
• The body's immune response to this bacterial growth and clogged pore causes swelling, redness, and the formation of pus. This results in the raised, red spot with a white tip that is recognized as a pimple.

Pimples can vary in severity. When the blockage is closer to the surface, it might form a whitehead or blackhead. When it is deeper and infected, it becomes an inflamed pustule, papule, nodule, or cyst. In summary, pimples form due to clogged pores from excess oil, dead skin cells, and bacterial growth causing inflammation and infection in the skin.