Acne is an inflammatory disease of the skin, caused by changes in the pilosebaseous units(skin structures consisting of a hair follicle and its associated sebaceous gland).

The most common form of acne is known as acne vulgaris, which means common acne. Excessive secretion of oils from the glands combine with naturally occurring dead skin cells to block the hair follicles.

Oil secretions build up beneath the blocked pore, providing a perfect environment for the skin bacteria Propionibacterium acnes to multiply uncontrolled. In response, the skin inflames, producing the visible lesion. The face, chest, back and upper arms are especially exposed.

The typical lesions of acne are: small whitish or skin-colored bumps whiteheads or blackish elevations blackheads. More inflamed rashes take the form of pus-filled, or reddish bumps, even boil-like tender swellings. After resolution of the lesions, prominent unsightly scars may remain.

The condition is common in puberty as a result of an abnormal response to normal levels of the male hormone testosterone. The response for most people diminishes over time and acne thus tends to disappear, or at least decrease, after one reaches the third decade of life.

There is, however, no way to predict how long it will take for it to disappear entirely, and some individuals will continue to suffer from acne decades later, into their thirties and forties and even beyond.

Acne affects a large percentage of humans at some stage in life. Aside from scarring its main effects are psychological, such as reduced self-esteem and depression. Acne usually appears during adolescence, when people already tend to be at their most socially-insecure. For this reason acne should be treated if severe.

Acne rosacea
Rosacea (ro-ZAY-she-ah) sometimes called "Adult Acne" occurs in people of all ages especially older woman when they go through menopause. The disorder is characterized by redness, pimples, and, in advanced stages, thickened skin. People who flush or blush easily are most at risk of developing rosacea.


Causes for acne
Exactly why some people get acne and some do not is not fully known. It is known to be partly hereditary. Several factors are known to be linked to acne:

Hormonal activity
Hyperactive sebaceous glands
Accumulation of dead skin cells
Bacteria in the pores
Skin irritation or scratching of any sort
Anabolic steroids
Birth control pills, however many women have reported reduced acne while on the pill
Those exposed to high levels of chlorine compounds, particularly chlorinated dioxins, often develop severe, long-lasting acne, known as Chloracne

Traditionally, attention has focused mostly on over-production of sebum as the main contributing factor of acne. More recently, more attention has been given to narrowing of the follicle channel as a second main contributing factor.

Abnormal shedding of the cells lining the follicle, abnormal cell binding ("hyperkeratinization") within the follicle, and water retention in the skin (swelling the skin and so pressing the follicles shut) have all been put forward as mechanisms involved, but there does not appear to be much conclusive medical research on the subject.


Acne misconceptions
Since the medical knowledge about acne is still relatively small, many misconceptions and rumors about what causes acne exist:

Diet. Chocolate, chips, sugar, milk and seafood among others have not been shown to affect acne. This means that the scientific studies done to date did not find a big difference between acne in two groups of people, one group eating the food in question and one group avoiding it.

It is possible that a given individual is sensitive to certain foods, but be sure to check that a flare-up happens again and again and again, whenever you eat the food you 'suspect'. It is quite easy to see false patterns in coincidences because one wants to find a cause to one's problem so badly.

Deficient personal hygiene. Acne is not caused by dirt. This misconception probably comes from the fact that blackheads by their nature are black and the acne infected skin, therefore, looks dirty. The blockages that cause acne occur deep within the narrow follicle channel, from the cells and sebum created there by your body. It is useful to clean your skin, but doing so will not prevent acne. Anything beyond very mild cleaning will make your skin worse because you'll damage it.

Sex. Rumors have had it that both celibacy and masturbation are causes for acne. This is not the case. It is notable however that masturbation and any other sexual activity affects hormone levels and thus bodily oil production.


Treatments
There is a myriad of products sold for the treatment of acne, many of them without any scientifically proven effects. However, a combination of treatments can greatly reduce the amount and severity of acne in many cases. There are four types of treatments that have been proven effective:

Killing the bacteria that are harbored in the blocked follicles. This is done either by the intake of antibiotics like tetracyclines, or by treating the affected areas externally with bactericidal substances like benzoyl peroxide (Benzac) or erythromycin (Ilosone).

However, reducing the P.acnes bacteria will not, in itself, do anything to reduce the oil secretion and abnormal cell behaviour that is the initial cause of the blocked follicles. Therefore, acne will generally reappear quite soon after the end of treatment - days later in the case of topical applications, and weeks later in the case of oral antibiotics.

Reducing the secretion of oils from the glands. This is done by a great daily oral intake of Vitamin A derivates like isotretinoin over a period of a few months. The product is sold by Roche under the names Accutane in USA and Roaccutane in Europe. Isotretinoin has been shown to be very effective in treating severe acne and is effective in up to 80% of the patients.
The drug has a much longer effect than anti-bacterial treatments and will often cure acne for good. The treatment requires close medical examination by a dermatologist since the drug has many known side effects (which can be severe). At the end of the initial treatment, about 25% of patients need to take a second treatment for another few months to obtain desired results.

The most common side effects are dry skin and nosebleed. It can also permanently damage the liver and cause depression. The drug also causes birth defects if women become pregnant while taking it.

Normalizing the follicle cell lifecycle. A group of medications for this are topical retinoids such as Tretinoin (brand name Retin-A), Adapalene (brand name Differin) and Tazarotene. They are also related to Vitamin A, just as Accutane in the previous entry, but put on your face instead of swallowed.

They can give significant irritation of the skin, but are probably rather less nasty than Accutane because less of it circulates in the bloodstream. The retinoids appear to influence the cell creation and death lifecycle of cells in the follicle lining. This helps prevent the hyperkeratinization of these cells that can create a blockage.

Exfoliating the skin. The topical treatment salicylic acid for example encourages the peeling of the top layer of skin to prevent a build-up of dead skin cells which combine with skin oil to block pores. It also helps to unblock clogged pores.

Benzoyl peroxide and the topical retinoids may be the best compromise between genuine effectiveness and negative side effects in many cases. The topical retinoids are relatively new and not as widely used as the other treatments as of the year 2004. It is highly advisable to ask a doctor or dermatologist about the tradeoffs between these treatments for any individual case.
Popping a pimple or any physical acne treatment should not be attempted by anyone but a qualified dermatologist. Pimple popping irritates skin, can spread the infection deeper into the skin and can cause permanent scarring.

Lasers have been in use for some time to reduce the scars left behind by acne, but research is now being done on lasers for prevention of acne formation itself. The laser is used to produce one of the following effects:

to burn away the follicle sac from which the hair grows
to burn away the sebaceous gland which produces the oil
to induce formation of oxygen in the bacteria, killing them

As of 2004, this is still mostly at the stage of medical research rather than established treatment.

Because acne appears to have a significant hereditary link, there is some expectation that cheap whole-genome DNA sequencing may help isolate the body mechanisms involved in acne more precisely, possibly leading to a more satisfactory treatment. (Crudely put, take the DNA of large samples of people with significant acne and of people without, and let a computer search for statistically strong differences in genes between the two groups). However, as of 2004 DNA sequencing is not yet cheap and all this may still be decades off.