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, shoulders and upper arms are especially affected.
The typical acne lesions are: comedones , papules, pustules and cysts. 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.
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
Birth control pills (however, many women have reported reduced acne while on the pill: this depends on the hormonal composition)
- Any medication containing halogens (iodides, chlorides, bromides), lithium, barbiturates, or androgens
- Exposure to high levels of chlorine compounds, particularly chlorinated dioxins, can cause 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.
Since the medical knowledge about acne is still relatively small, there are many misconceptions and rumours about what causes the condition:
Diet. Chocolate, chips and sugar, 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. However, one recent study , based on a survey of 47,335 women, did find a positive association between milk consumption and acne. The researchers hypothesize that the association may be caused by the hormones in milk. Seafood, on the other hand, may contain relatively high levels of iodine, but probably not enough to cause an acne outbreak. Still, people who are prone to acne may want to avoid excessive consumption of foods high in iodine.
- Deficient personal hygiene. Acne is not caused by dirt. This misconception probably comes from the fact that acne basically involves skin infections. In fact the blockages that cause acne usually occur deep within the narrow follicle channel, where it is usually impossible to wash them away, from the cells and sebum created there by your body. The bacteria involved are exactly the same bacteria that everyone has on their skin. It is useful to clean your skin, but doing so will not prevent acne. Anything beyond very gentle cleansing can actually worsen existing lesions and even encourage new ones by damaging or overdrying skin.
Sex. Common myths state that either celibacy or masturbation cause acne. There is no scientific evidence that this is the case. It is true, however, that sexual activity, as well as anger and stress, affect hormone levels and thus bodily oil production.
There are many 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. It is highly advisable to ask a dermatologist about the tradeoffs between these treatments for any individual case, especially when considering using any of them in combination. There are a number 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 or erythromycin. 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, some studies suggest, cause depression. Because of this, the drug is typically used given a last resort after milder treatments have proven insufficient. The drug also causes birth defects if women become pregnant while taking it. For this reason, female patients are required to either use birth control or vow abstinence while on the drug.
- 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 . Like Accutane/Roaccutane, they are related to Vitamin A, but they are administered as topicals and generally have much milder side effects. 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. Retinol, a form of Vitamin A, has similar but milder effects and is used in many over-the-counter moisturizers and other topical products. The topical retinoids are relatively new and not as widely used as the other treatments as of the year 2004.
- Exfoliating the skin. This can be done either mechanically, using an abrasive cloth or a liquid scrub, or chemically. Common chemical exfoliating agents include salicylic acid and glycolic acid , which encourage 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 already clogged pores. Note that the phrase "peeling" is not meant in the visible sense of shedding, but rather as the destruction of the top layer of skin cells at the microscopic level. Depending on the type of exfoliation used, some visible flaking is possible. Moisturizers and anti-acne topicals containing chemical exfoliating agents are commonly available over-the-counter.
- Phototherapy. It has long been known that short term improvement can be achieved with sunlight. However studies have shown that sunlight worsens acne long-term, presumably due to UV damage. More recently, visible light has been successfully employed to treat acne- in particular intense blue light generated by purpose-built fluorescent lighting, or lasers. Used twice weekly, this has been shown to reduce the number of acne by about 64% . The mechanism appears to be that the porphyrins generated by the P. acnes, under irradiation by blue light, generate free radicals damaging, and if consistently applied over several days, ultimately kill the bacteria . Extensive basic science and clinical work first initiated by dermatologists Yoram Harth and Alan Shalita have shown that intense blue/violet light (405-425 nanometer) can decrease the number of inflammtory acne lesion by 60-70% in 4 weeks of therapy. Since porphyrins are not otherwise present in skin, and no UV light is employed, it appears to be safe, and has been licensed by the U.S. FDA . However, the equipment is relatively expensive; several hundred US dollars upwards (c. 2004), and works best for mild-moderate acne.
Less widely used treatments include:
- Azelaic acid (brand names Azelex, Finevin, Skinoren). 
- Zinc. Orally administered zinc gluconate has been shown to be effective in the treatment of inflammatory acne, although less so than tetracyclines.  
- Alternative treatments. Nicholas Perricone's controversial book The Acne Prescription proposes an alternative treatment for adult acne, including a strict diet and topicals containing alpha lipoic acid. Perricone's claims do not seem to be backed up by strong scientific evidence. There are no double-blind studies proving the effectiveness of fatty acids against acne.
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
Since lasers and intense pulsed light sources cause thermal damage to the skin there are concerns that laser or intense pulsed light treatments for acne will induce hyperpignmented macules (spots) or cause long term dryness of the skin. As of 2005, 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 2005 DNA sequencing is not yet cheap and all this may still be decades off. It is also possible that gene therapy could be used to alter the skin's DNA.
Rosacea (ro-ZAY-she-ah) sometimes called "Adult Acne" occurs in people of all ages, especially older women when they go through menopause. Two famous men with the affliction are W.C. Fields and former United States President Bill Clinton. 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.
Severe acne often leaves small scars where the skin gets a "volcanic" shape. Acne scars are very hard (and expensive) to treat and it is unusual for the scars to be successfully removed completely. In those cases, scar treatment may be appropriate. The most commonly used forms of scar treatments are:
Dermabrasion. The top layer of the skin is removed to make the scar look less pitted. It makes the scar less visible but does not remove it completely. Multiple treatments may be necessary to get the desired results. This procedure is usually performed by a cosmetic surgeon.
- Microdermabrasion is a newer technique that has a similar effect to traditional dermabrasion, but is less radical. While dermabrasion is a surgical procedure, microdermabrasion is performed by blasting tiny crystals at the skin. Many dermatologists and cosmetic surgeons offer this procedure.
- Laser resurfacing . A laser is used to burn off the top layer of the skin. This procedure is commonly known by the brand names of the machines used to perform it, including SmoothBeam . Many dermatologists and cosmetic surgeons offer this procedure.
- Punch excision . The scar is excised with a punch tool and the edges are sutured together. This procedure is usually performed by a cosmetic surgeon.
- Chemical peels (also known as acid peels ). A type of organic acid, most commonly glycolic , salicylic, or lactic, is applied to the skin so that a smoother layer can surface. Despite its unpleasant name, this procedure is painless if performed properly and requires no anaesthetic. Peels are typically performed several times over a period of weeks or months. The procedure can also be beneficial for active acne. Many dermatologists and cosmetologists offer this procedure, although the peels given by dermatologists are generally of a higher concentration and therefore potentially more effective.
- Subcision . The scar is detached from deeper tissue, allowing a pool of blood to form under the scar which helps form a connective tissue under the scar, levelling it with the surface. This procedure is usually performed by a cosmetic surgeon.
- Dermal filler . The scar is filled with an injectable dermal filler like Bio-Alcamid®
Keratosis pilaris is a skin condition that is often confused with acne.
- James, W. D. (2005, April 7). Acne. In The New England Journal of Medicine, 352, 1463 – 1472.