How Blemishes Form
2. This extra oil can block the pore, which is the opening in the skin where sebum normally flows out. Sebum and dead skin cells can build up behind the blockage to create a comedone (blackhead or whitehead).
3. The environment inside the blocked pore is airtight, providing an ideal home for bacteria called P. acnes, which thrive in airless conditions. These bacteria lead to the inflammation under the skin that causes the red, painful effects of acne.