The oil i.e. sebum produced by the oil glands get drained to the surface of the skin gets blocked and bacteria grow there and it start to form acne.
There are two types of acne 1) non-inflammatory acne and 2) inflammatory acne. Anti-inflammatory acne is further divided into whiteheads and blackheads. Whiteheads are the small white spots which are sometimes invisible to naked eyes. Blackheads are formed when the pores open to the surface which contains skin pigment melanin, black in color. An inflammatory acne is of two types i.e. papule and pustule. A papule is form due to the breakage in the follicular wall and pustule is form after white blood cells rush in and it becomes inflamed.
There are various factors responsible for the formation of acne which is listed below:
1) Hormones: Hormones are the primary cause for the formation of acne. During puberty because of the released of the sex hormone from the body. These hormones stimulate the oil glands to produce more oil and it results into clogging and ultimately results into acne.
2) The second reason is stress. Hormonal changes occur in the body due to stress and it causes the oil glands to produce more oil which results in the formation of acne.
3) Genetic factor: You can get acne if any your family members had acne in the past.
4) False food habits: It is also depends on the type of food you consume.
5) Diseases: Because of diseases like diabetes, polycystic ovaries and ovarian tumor also acne can form.
6) Environmental factors: There are some environmental factors like dirt, pollution which initiates the acne formation.
7) Oily skin or hair: The excess of oil on the face and hair can also cause the blockage of pores as the extra oil attracts dust particles.
8) Side effects of drugs: There are oral drugs or topical creams available whose side effects can result into the formation of acne.