There mare mainly three things that cause acne. They are over production of oil called as sebum, the irregular shading of dead skin tissue which irritates the hair follicles and the growth of bacteria in the hair follicles. When the hair follicles get blocked by the oil, sebum and the skin debris acne develop. The oil producing sebaceous glands are connected to the hair follicles.

The produced oil reaches the skin surface by traveling along the hair shaft. When the oil sebum and the dead cells are in larger amounts they block the skin pores and the acne are caused. When there is an inflammation or infection of the blocked hair follicle then pimple develop. If the clogs and inflammation are deep inside the skin then lumps are produced just below the skin called as cysts. The pores which are openings of the sweat glands generally do not develop acne.

• The increased production of the oil sebum is due to heredity, hormones, bacteria and some medications. Use of harsh soaps to clean the pores or too much cleaning make the skin dry and worsens the acnes.
• Since hormone is one of the contributing factor in development of acne the condition in which there are hormonal changes in the body can develop acne like teenage girls and boys (puberty), pregnancy, two to seven days before the menstrual periods, use of certain medications and use of cortisone.
• Exposure of oily or greasy skin to direct sun, use of cosmetics directly on skin, family history of acne and rubbing or pressure to skin are the risk factors for the development of acne.
• Use of oily lotions, creams and other cosmetic products can cause acne. Improper removal of make up or allowing the make up to dry on face also can cause acne. Role of intake of oily food in development of cane is a debatable issue.
• Constipation is also considered as one of factors in development of acne.
• Contact with the irritants, tight fitting cloths, not washing the face, squeezing the blemishes and use of harsh soaps can cause acne to develop. Intake of saturated partially hydrogenated fats, red meat, high fat foods, margarine, reheated oils and fried foods can cause acne.  Lack of balanced diet can cause acne. Physical and mental stress also causes acne to develop.  Starting or discontinuing the birth control pills also causes acne to develop.