Final answer:
A blackhead is caused by the accumulation of sebum produced by sebaceous glands. These glands secrete an oily substance that can block hair follicles when overproduced, leading to the formation of a plug that turns black upon exposure to air.
Step-by-step explanation:
A blackhead is an accumulation of oily material produced by sebaceous glands. These glands are located in the dermis of the skin and secrete an oily substance called sebum. Sebum has several functions, including waterproofing the hair and skin, preventing them from drying out, and inhibiting the growth of microorganisms on the skin due to its antibacterial properties. When sebum, along with keratin, overproduces and accumulates, it can block hair follicles. This blockage forms a plug that initially appears white and turns black upon oxidation when exposed to air, hence the typical appearance of a blackhead.
To prevent acne, which includes the formation of blackheads, it is recommended to clean the skin daily with a mild soap to remove excess oil and dirt. Although sweat glands also play a role in skin health by secreting sweat to cool the body and remove waste products, they are not responsible for the formation of blackheads.