Acne is a common  skin disease, characterized by areas of skin with multiple non-inflammatory follicular papules or comedones and by inflammatory papules, pustules, and nodules in its more severe forms. Acne mostly affects the areas of skin with the densest population of sebaceous follicles; these areas include the face, the upper part of the chest, and the back. Severe acne is inflammatory, but acne can also manifest in noninflammatory forms. Acne lesions are commonly referred to as pimples, blemishes, spots or simply acne. Acne lesions are caused by changes in pilosebaceous units, skin structures consisting of a hair follicle and its associated sebaceous gland, changes which require androgen stimulation.
Acne occurs most commonly during adolescence, affecting more than 96% of teenagers, and frequently continues into adulthood. In adolescence, acne is usually caused by an increase in male sex hormones, which people of both genders accrue during puberty. For most people, acne diminishes over time and tends to disappear or at the very least decrease after one reaches one's early twenties. There is, however, no way to predict how long it will take to disappear entirely, and some individuals will carry this condition well into their thirties, forties and beyond.
The face and upper neck are the most commonly affected, but the chest, back and shoulders may have acne as well. The upper arms can also have acne, but lesions found there are often keratosis pilaris, not acne. Typical acne lesions are comedones, inflammatory papules, pustules and nodules.

Causes of acne
Acne develops as a result of blockages in follicles. Hyperkeratinization and formation of a plug of keratin and sebum (a microcomedo) is the earliest change. Enlargement of sebaceous glands and an increase in sebum production occur with increased androgen (DHEA-S) production at adrenarche. The microcomedo may enlarge to form an open comedone (blackhead) or closed comedone (whitehead). Whiteheads are the direct result of sebaceous glands becoming clogged with sebum, a naturally occurring oil, and dead skin cells. In these conditions the naturally occurring largely commensal bacteria Propionibacterium acnes can cause inflammation, leading to inflammatory lesions (papules, infected pustules, or nodules) in the dermis around the microcomedo or comedone, which results in redness and may result in scarring or hyperpigmentation. 
Primary causes
Acne is known to be partly hereditary, but no particular genetic cause has been identified. Acne is not contagious or infectious. Several factors are known to be linked to acne:
•    Family/Genetic history. The tendency to develop acne runs in families. For example, school-age boys with acne often have other members in their family with acne as well. A family history of acne is associated with an earlier occurrence of acne and an increased number of retentional acne lesions.
•    Hormonal activity, such as menstrual cycles and puberty. During puberty, an increase in male sex hormones called androgens cause the follicular glands to grow larger and make more sebum.
•    Inflammation, skin irritation or scratching of any sort will activate inflammation.
•    Stress.
•    Hyperactive sebaceous glands,
•    Bacteria in the pores. Propionibacterium acnes (P. acnes) is the anaerobic bacterium that causes acne.
•    Use of anabolic steroids
•    Exposure to certain chemical compounds. Chloracne is particularly linked to toxic exposure to dioxins, namely Chlorinated dioxins.

Several hormones have been linked to acne: the androgens testosterone, dihydrotestosterone (DHT) and dehydroepiandrosterone sulfate (DHEAS), as well as insulin-like growth factor 1 (IGF-I).
Others include Diet- Chocolate, Milk, Carbohydrates, Vitamins A and E.

What are some common acne symptoms? Surprisingly, signs of acne can go way beyond that typical pimple.
Acne vulgaris, or common acne, is a disorder of the pilosebaceous unit, causing some form of lesions on the skin. Acne is characterized by the presence of one or more of the following:
•    Papules
•    Pustules
•    Blackheads
•    Whiteheads or milia
•    Nodules
•    Cysts
What are the type of Acne
Acne can be divided into two categories: inflamed and non-inflamed. Non-inflamed acne breakouts consist of microcomedones, blackheads, and milia. These types of comedones are not red or painful. Symptoms of non-inflamed acne include bumps or bumpiness across the skin's surface, or an uneven skin texture. Even if comedones are not readily visible, they will make the skin feel rough or "sandpapery." People with non-inflamed acne experience blackheads, milia, and closed comedones but rarely have reddened breakouts, such as papules or pustules. Left untreated, non-inflamed acne may progress to inflamed acne.

Inflamed Acne
Inflamed acne is characterized by redness and inflammation. Those with inflamed acne will have microcomedones, blackheads, and milia, as well as papules, pustules, and possibly nodules and cysts. Symptoms also include redness, swelling, and irritation of the skin, along with possible crusting, oozing, or scabbing of the lesions. Inflamed acne ranges in acuity from very mild to extremely severe. Some inflamed acne sufferers will experience only the occasional pustule while others will battle angry-looking cysts. Cystic acne is the most serious form of inflamed acne. Inflamed acne sufferers are most at risk for skin damage and scarring.

Doctor can diagnose acne based on the appearance of the skin. Testing is usually not required.

Acne treatment depends on whether you have a mild, moderate, or severe form. Sometimes your doctor will combine treatments to get the best results and to avoid developing drug-resistant bacteria. Treatment could include lotions or gels you put on blemishes or sometimes entire areas of skin, such as the chest or back (topical medicines). You might also take medicines by mouth (oral medicines).


Treatment for mild acne ( whiteheads, blackheads, or pimples) may include:
•    Gentle cleansing with a mild soap.
•    Applying benzoyl peroxide (such as Benzyl Peroxide).
•    Applying salicylic acid.

If these treatments do not work, you may want to see your doctor. Your doctor can give you a prescription for stronger lotions or creams. You may try an antibiotic lotion. Or you may try a lotion with medicine that helps to unplug your pores.

Moderate to severe acne
Sometimes acne needs treatment with stronger medicines or a combination of therapies. Deeper blemishes, such as nodules and cysts, are more likely to leave scars. As a result, your doctor may give you oral antibiotics sooner to start the healing process. Inflammatory acne may need a combination of several therapies. Treatment for moderate to severe acne may include:
•    Applying benzoyl peroxide.
•    Draining of large pimples and cysts by a doctor.
•    Applying prescription antibiotic gels, creams, or lotions.
•    Applying prescription retinoids.
•    Applying azelaic acid.
•    Taking prescription oral antibiotics.
•    Taking prescription oral retinoids (such as isotretinoin).
Treatment for acne scars
Treatment may improve and even remove acne scars. Sometimes a combination of treatments works best. These treatments include:
•    Collagen injections, which smooth the skin by plumping the skin under the scar.
•    Dermabrasion, which uses a whirling wire brush to skim off scar tissue.
•    Laser resurfacing, which uses a carefully controlled laser to burn away scar tissue.
•    Chemabrasion, which uses chemicals to peel away top layers of skin.
•    Most treatments for acne take time. It often takes 6 to 8 weeks for acne to improve after you start treatment. 1 Some treatments may cause acne to get worse before it gets better.
•    If your acne still hasn't improved after several tries with other treatment, your doctor may recommend that you take an oral retinoid, such as isotretinoin (Accutane). Doctors prescribe this medicine as a last resort, because it has some rare but serious side effects and is expensive.
•    Certain low-dose birth control pills may help control acne in women who tend to have flare-ups before menstruation.

Complications
Acne scarring: Acne scarring can sometimes develop as a complication of acne when the most serious types of spots, nodules and cysts, rupture (burst) damaging nearby skin. Scarring can also occur if you pick or squeeze your spots, so it is important to avoid doing this.

Precautions and Preventions
Acne can tremendously embarrassing for the acne sufferer. It is advisable to maintain the right kind of diet, nutritional balance and proper skin care. Here are some tips that will help you heal your acne:
•    Use an astringent to remove the excess oil.
•    Although moisturizing is not advisable on a daily basis, oil-free moisturizers can be applied if your skin is rough after washing.
•    It is advisable to choose water-based products, rather than products containing oil or petroleum.
•    Apply a honey mask once a week. Honey is regarded as a disinfectant and also it has medicinal properties believed to heal minor blemishes. It has the properties of destroying the bacteria present in the skin.
•    It is advisable to wash your face at least twice a day with sulfur-based soap. Once when you wake up and again when you go to bed. Do not scrub; just give it a smooth touch. Washing your skin over and over again will create more trouble than help you.
•    If you have long hair it is advisable to cut it short. Your hair contains oil and when you move, the dust particles do mix up with your hair and when your hair bangs on your face or neck or forehead or the affected area, the situation could worsen. Also wash your hair on a daily basis.
•    Take a multi-vitamin daily. Your skin needs proper nutrition.
•    It is advisable to take a chromium supplement once a day, as it will heal your pimples quickly.
•    Vitamin A protects the skin and prevents acne. It also helps reduce sebum production.
•    While going to bed make sure to remove your makeup and it is also advisable not to use any kind of cold cream and lotions. If you really want to wear makeup, make sure that it is water-based.
•    Drink at least 8 glasses of water daily. Water helps in cleaning and hydrating the skin and maintaining overall health.
•    Don't pop or squeeze pimples, as it could lead to inflammation and infection. It could also push the infected materials deep into the skin and create more swelling. Squeezing or popping pimples could lead to permanent scars on the face.
•    Alcohol-based lotions and creams are to be avoided completely.
•    Wash or change your pillowcase every day.
•    Zinc is an antibacterial agent. A diet low in zinc can cause acne breakouts. First use warm water to wash the face (to remove dirt) and use cold water to rinse.
•    If you get acne on your body, it is advisable not to wear tight clothes.
•    People with acne should avoid sun exposure and use UVA/UVB sunscreen. Oil-based sunscreen should be avoided.
•    Eat plenty of fresh fruits and vegetables daily.
•    Exercise moderately as it helps in blood circulation and helps eliminate toxins.
•    It is advisable to breathe deeply when you feel stressed. Doctors have found out that there is a direct link between stress and acne. Studies have shown that there is increased amount of androgen production when a person is under stress. Not only mental but physical stress such as allergies, surgery etc, could activate the androgen production. When androgen is activated the sebaceous glands pumps out more oil/sebum leading to acne.