Acne, medically known as Acne Vulgaris, is a skin disease that involves the oil glands at the base of hair follicles. 

It commonly occurs during puberty when the sebaceous (oil) glands come to life - the glands are stimulated by male hormones produced by the adrenal glands of both males and females.

The word acne comes from the word acme meaning "the highest point", which comes from the Greek akme meaning "point" or "spot" - it was originally misspelt, with an 'n' rather than an 'm' in 1835. 

Skin cells, sebum and hair can clump together into a plug, this plug gets infected with bacteria, resulting in a swelling. A pimple starts to develop when the plug begins to break down.

American Academy of Dermatology (AAD) describes that acne appears when a pore in our skin clogs. This clog begins with dead skin cells.

Normally, dead skin cells rise to surface of the pore, and the body sheds the cells. When the body starts to make lots of sebum (see-bum), oil that keeps our skin from drying out, the dead skin cells can stick together inside the pore. Instead of rising to the surface, the cells become trapped inside the pore.

Sometimes bacteria that live on our skin, p. acnes, also get inside the clogged pore. Inside the pore, the bacteria have a perfect environment for multiplying very quickly. With loads of bacteria inside, the pore becomes inflamed (red and swollen). If the inflammation goes deep into the skin, an acne cyst or nodule appears.

Mayo clinic lists three factors for occurrence of acne. They are as follows:

• Overproduction of oil (sebum)- Hair follicles are connected to sebaceous glands. These glands secrete an oily substance known as sebum to lubricate your hair and skin. When your body produces an excess amount of sebum and dead skin cells, the two can build up in the hair follicles and form together as a soft plug, creating an environment where bacteria can thrive.

•  Irregular shedding of dead skin cells resulting in irritation of the hair follicles of your skin

• Build-up of bacteria- •   When the oil is trapped inside the skin pores, some bacteria are produced which alter the composition of oil and it results in skin irritation.

Factors that may worsen acne:

These factors can trigger or aggravate an existing case of acne:

• Hormones. Androgens are hormones that increase in boys and girls during puberty and cause the sebaceous glands to enlarge and make more sebum. Hormonal changes related to pregnancy and the use of oral contraceptives can also affect sebum production.
• Certain medications. Drugs containing corticosteroids, androgens or lithium are known to cause acne.
• Diet. Studies indicate that certain dietary factors, including dairy products and carbohydrate-rich foods — such as bread, bagels and chips, which increase blood sugar — may trigger acne.