A pimple begins when a hair follicle becomes blocked with excess oil and dead skin cells, trapping material beneath the skin. If the blockage stays closed, it forms a whitehead, where oil and cells are sealed under the surface. If the pore remains open, oxygen darkens the trapped material, creating a blackhead. When bacteria start multiplying inside a blocked follicle, the immune system responds, leading to redness and swelling called a papule. As the immune response continues, white blood cells