Blackhead, yellowish or blackish plug of material accumulated in the duct of a sebaceous gland. The material consists of keratin (horny cells of the epidermis) and modified sebum (oily secretions of the sebaceous gland). Blackheads are the primary lesions in acne.

Blackhead is caused when excess skin oil, sebum and congesting toxins are expelled through your skin from the blood and lymph fluid that supplies your skin with nutrients. These congesting toxins combined with skin oil and sebum clogs your pores causing blackheads, whiteheads, and full blown acne.