Acne is a skin problem that affects the skin's oil glands.
An oily substance known as sebum is made by these glands.
And these are connected to the pores by a follicle.
An acne develop when the follicle of a skin oil glands clog up.
The main cause of acne is not known by the doctor.
But the health care providers believe that it may cause by many related factors.
An increase in hormones levels is the main factor, known as androgens.
During puberty, the levels of hormones increased in both male and females.
The changes in hormones linked to pregnancy or sometimes, acne is associated by beginning or stopping of birth control pills.
Genetics or heredity is other factor of acne.
For examples, various students who are suffered from acne have a family history of this disease.
In some cases, acne is caused by certain medications containing lithium and androgens.
The cells of the follicles are altered by oily or greasy cosmetics and making a plug.
The other triggers that are developed acne may include:

• Skin squeezing or picking
• Humidity
• Menstrual periods
• Skin rubbing
• Pollution
• Skin scrubbing
• Stress

The health care providers defined it as a disorder of the pilosebaceous units.
It is found mostly parts of the body.
Pilosebaceous units include sebaceous glands that are connected to a follicle, and consist a hair.
These units are found on the upper back, chest and face.
The sebaceous glands produce a greasy substance known as sebum.
Cells (keratinocytes) line the follicle.
The keratinocytes, hair and sebum may make a plug.
The sebum is prevented by plug from skin by a pore.
Bacteria Propionibacterium acnes are allowed by the mixture of cells and oil.
Then bacteria make enzymes and chemicals and added with white blood cells.
The basic lesion of acne is known as comedo that is plugged hair follicle and large in size.
The types of lesions include pustules, cysts, papules and nodules.

1. Pustules- they appear in red color at the base and are pus-filled lesions
2. Cysts-harmful, pus-filled and deep lesions which can leave scar after healing
3. Papules- they are appeared in pink color bumps on the surface of the skin and they are inflamed lesions.
   
4. Nodules- harmful, large in size and hard lesions that are occurred deep within the skin.
   

The changes in the levels of hormones can develop acne after adolescence.
In some cases, women feel acne during the period of pregnancy.
Other factors of acne include pressure from backpacks, tight collars, and bike helmets and environmental irritants.