Acne vulgaris is a common, chronic and recurring disease that involves multiple etiological factors including follicular hyperkeratinization, increased sebum production, Propionibacterium acnes proliferation and inflammation. It affects about 80% of teenagers and young adults and is most prevalent in those aged 12 to 24 years, although it can occur at all ages. As many as 17 million people are thought to be affected in the United States alone and the acne therapeutics market is forecast to show moderate growth in revenues through 2016; market data suggests the global acne market was worth US $2.8 billion in 2009 and is estimated to reach revenues of $3.02 billion by 2016. This moderate increase in revenue is attributed to an overcrowding of the market with generics and increased consumer acceptance of alternative therapies, although the acne therapeutics market is witnessing a shift toward combination products using two or more effective acne treatments.
One of the major causes of acne is the increase in sex hormones, especially androgens such as testosterone, which occurs during puberty. Testerone is converted in the skin to dihydrotestosterone (DHT) by α-reductase, which stimulates the sebaceous glands to enlarge and produce more sebum. The more sebum produced, the worse the acne will become. Further, a study by Lee et al. suggests that DHT may also be involved in the production of proinflammatory cytokines in acne.
Abnormal follicular keratinization is also involved in the development of acne vulgaris. The presence of unsaturated fatty acids in sebum alter the calcium dynamics in epidermal keratinocytes and induce abnormal follicular keratinization,4 and if sebum and keratin block the skin pores, they can cause comedones—small, skin-colored bumps or papules—to develop and hair follicle walls to rupture. Further, bacterial and comedonal debris cause acne pimples or pustules, i.e., inflammatory lesions.
Acne typically appears on the oil-producing areas of the body, namely the face, chest and back, and can have short-term, potentially lasting psychological effects such as decreased self-esteem and self-confidence leading to social withdrawal and even depression. While the three levels of acne severity are generally considered mild, moderate or severe, even mild acne can be troublesome, especially to teenagers who see each pimple as a major cosmetic challenge.
Interestingly, using a genetic-based strategy, Bek-Thomsen et al. recently demonstrated that follicles from healthy skin were exclusively colonized by P. acnes, whereas the follicular microbiota of acne patients included, in addition to P. acnes, Staphylococcus epidermidis and minor proportions of other species.5 However, previous studies excluded Staphylococci as agents that play a role in the pathogenesis of acne due to their rapid development of resistance to therapeutic antibiotics.6 The presence of S. epidermidis exclusively in acne-affected follicles raises the question of the potential role of this species in acne.