What causes pimples?

Pimples are lesions of substantial protuberances within 0.5 mm in diameter. Pimples can be red, black, brown, white, etc. For causes, there are generally allergic, such as eczema; infectious, such as warts, warts caused by papules; like syringoma is also a flat papule, rice grain size, this is a tumor; like pigmented nevus, it is a nevus cell accumulation, but also a papule; immune, like lichen planus; metabolic, such as amyloidosis.