What causes pimples on the scalp?

Pimples on the scalp occur when pores become blocked, according to HowStuffWorks. Just like on the face and back, a protective oil layer known as sebum forms in the skin on the scalp. Sebum rises to the skin's surface through pores, which become clogged with skin cells and excess oil.

Microcomedones, precursors to pimples, form when bacteria reproduce in trapped sebum, notes HowStuffWorks. When a microcomedone grows, it becomes a comedone, also known as a whitehead or blackhead. Comedones sometimes become inflamed and fill with pus, leading to pimples.

Blockage of pores can be caused by hormones and too much oil produced by the skin, according to HowStuffWorks. The presence of hair can contribute to sebum building up on the scalp. Some hair styling products also include ingredients that can cause pores to become clogged.