A pimple, zit or spot is a kind of acne, and one of the many results of excess oil getting trapped in the pores. Some of the varieties are pustules or papules. Pimples can be treated by various acne medications prescribed by a dermatologist, or purchased at a drug store with a wide variety of treatments.

A pimple, also known as a zit or spot is a small papule or pustule; small skin lesions or inflammation of the skin - they are oil glands (sebaceous glands) that are infected with bacteria, become inflamed, and then fill up with pus.

Pimples are caused when the sebaceous glands located at the base of hair follicles become overactive; the most vulnerable parts of the body are the face, back, chest and shoulders. Pimples are palpable signs of acne, especially when a breakout occurs.
According to Medilexicon's medical dictionary:

The sebaceous glands are tiny skin glands which secrete sebum - an waxy/oily substance - to lubricate the skin and hair of mammals (humans are mammals).

In human beings they exist throughout all skin sites except the palms and soles; there is a greater abundance of sebaceous glands on the face and scalp. In our eyelids, meibomian sebaceous glands secrete a special type of sebum into tears.

Several medical conditions are linked to an abnormality in sebaceous gland function, including:
  • Acne (pimples).
  • Sebaceous cysts - closed sacs or cysts below the surface of the skin.
  • Hyperplasia - the sebaceous glands become enlarged, producing yellow, shiny bumps on the face.
  • Sebaceous adenoma - a slow-growing tumor (benign, non-cancerous) usually presenting as a pink, flesh-colored, or yellow papule or nodule.
  • Sebaceous gland carcinoma - an aggressive (cancerous) and uncommon skin tumor.
If a breakout occurs, doctors recommend that they be treated promptly to prevent the risk developing severe acne. There is also the danger that untreated severe acne may result in visible scars on the skin.

The sebaceous glands, which produce sebum, exist inside the pores of our skin. The outer layers of our skin are being shed continuously.

Sometimes, dead skin cells are left behind and get stuck together by the sticky sebum, causing a blockage in the pore.

Pore blockage is more likely to occur during puberty (the process of physical changes by which a child's body becomes an adult body capable of reproduction). More sebum is produced by the sebaceous gland - as the pore is blocked, it accumulates behind the blockage.

This accumulated and blocked sebum has bacteria, including Propionibacterium acnes; this slow-growing bacterium is linked to acne. Propionibacterium acnes generally exists harmlessly on our skin - however, when the conditions are right, it can reproduce more rapidly and become a problem. The bacterium feeds off the sebum and produces a substance that causes an immune response, leading to inflammation of the skin and spots.

The skin of people who are prone to acne are especially sensitive to normal blood levels of testosterone - a natural hormone found in both males and females. In such people the testosterone can make the sebaceous glands produce too much sebum, making the clogging up of dead skin cells more likely, which in turn increases the probability of blocking the pores, etc.

You cannot catch pimples from another person; they are not infectious.

There is no scientifically compelling evidence to prove that pimples are caused by diet.

Having pimples or acne can be hereditary.
Source : medical news