The white matter found in pimples is pus made of dead skin cells, oil and bacteria. Sebum, a natural oil produced in the skin, gets trapped under the surface and forms a plug. It can also mix with bacteria in hair follicles and cause inflammation.
Pimples contain the bacteria to keep them from spreading. Squeezing them breaks the skin and can cause the bacteria to spread, leading to infection. It can also result in permanent scarring. Topical treatments such as benzoyl peroxide or retinol are generally effective treatments. Pimples can sometimes be prevented by exfoliation, which removes dirt and dead skin cells on the surface and reduces the chance of a breakout. Common causes of pimples include stress, hormonal changes and poor diet.