A whitehead, also known as a ‘closed’ comedo or pimple, is one of the most common types of acne.
These occur when extra sebum produced in the follicle mixes with the faster shedding dead skin cells. They “stick” together and create a plug in the follicle (pore) under the surface of the skin. This traps oil and bacteria in the follicle below the skin’s surface. The white debris you see above the skin's surface is composed of trapped oil, dead skin cells and white blood cells.
A blackhead, also known as an ‘open’ comedo, is a common result of your skin’s natural processes.
Although many people think they are caused by dirt, this is not true. They occur if the plug of a developing whitehead enlarges and widens the pore. This action exposes the oil to the air and causes it to oxidise, which causes the black or grey colour.
A papule, is basically a small inflamed whitehead.
They are small, hard cone-shaped bumps like whiteheads, that are pink in colour and tender to touch; however, they do not usually contain any substance in them.
A pustule is a larger whitehead that has a yellow or white center with a red base.
These occur when a plug is formed deep inside a pore and it attracts white blood cells to help fight the infection. The more inflamed it becomes, the redder and larger the pustule. Like whiteheads, the white debris you see above the skin's surface is composed of trapped oil and dead white blood cells; however, there is more substance in these than a whitehead given they are deeper in the pore.