What pore impaction forms when sebum hardens and the sebaceous duct becomes clogged?

When sebum hardens and clogs the sebaceous duct, it leads to the formation of a comedo, commonly known as a blackhead or whitehead. In the case of a blackhead, the clogged pore remains open, allowing the oxidized sebum to darken at the surface. Conversely, a whitehead forms when the clogged pore is closed, trapping the sebum beneath the skin. Both conditions are a result of the accumulation of oil and dead skin cells.