Blemish-prone skin is skin that has a propensity to develop comedones and pimples. It is often oily and appears shiny. This is because the sebaceous glands produce more sebum than in other skin types.  The cause of a blemish is the clogging of pores with dead skin cells and excessive oil, which results in acne. When this happens in the upper layers of the epidermis, we get whiteheads and blackheads. However, when this happens in the inner layers, we end up with acne. Acne leaves our skin red and inflamed, which then turns into a blemish once the pimple goes away.