Acne is a disease of the human sebaceous follicle that occurs most commonly during adolescence and affects an estimated 80 to 90 percent of teenagers in the western world. With a prevalence of 22 to 32 percent worldwide, acne is the most common dermatological disease and the most common dermatological reason for medical consultation.

In 2010, acne was estimated to affect 650 million people globally, making it the eighth most common disease worldwide. The global anti-acne treatment market was $3.9 billion in 2013 and is estimated to reach $ 4.4 billion by 2020.

Acne Cause and Physical Response

Acne is caused by excessive oil production (sebum) caused by hormonal changes due to puberty and menstruation. The excessive oil production along with dead skin cells leads to clogged pores, which allows bacteria like Propionibacterium acnes (P. acnes) to proliferate. These clogged pores manifest themselves as white- or blackhead pimples.

P. acnes is a relatively slow-growing, anaerobic, gram-positive bacteria that uses sebum, cellular debris and metabolic byproducts as their primary sources of energy and nutrients. The presence of P. acnes causes an inflammatory skin response, leading to the development of inflamed red lesions. The oxidation of squalene in sebum to squalene hydroperoxide also significantly contributes to this response.

Acne Treatment Strategies

Current acne treatment strategies include correcting follicular keratinization using keratolytics, decreasing sebum, decreasing P. acnes using antimicrobial agents and reducing irritation using anti-inflammatory agents. These multiple strategies suggest using actives—or a combination of actives—that work by multiple mechanisms should lead to better efficacy.

Prescription retinoic acid is the only current therapy that is effective against all four mechanisms of action. All prescription therapies are either retinoids or antibiotics.

Prescription retinoids include Avita, Differin (adapalene), Retin-A (tretinoin), Tazorac (tazarotene), and Accutane. The most common oral antibiotics include clindamycin, doxycline, erythromycin, and tetracycline (oral). Clindamycin is also used topically.

Current over-the-counter monographed actives in the U.S. include salicylic acid (SA) from .5 to 2 percent, benzoyl peroxide (BPO) from 2.5 to 10 percent, and a combination of sulfur and resorcinol. All work as antimicrobial agents with SA also having keratolytic activity.

Salicylic acid should be formulated at a pH of ~3 to maximize its antimicrobial and keratolytic activity. A 2 percent SA lotion will reduce inflamed and noninflamed lesions by around 50 percent after four weeks, on average.

Benzoyl peroxide is normally used as a micronized powder in formulations due to its instability when solubilized. Ten percent BPO is quite irritating to skin and only incrementally better than using 2.5 percent BPO, which has much better skin compatibility. In the literature, it has been reported that 5 percent BPO reduces noninflamed lesions by 32 to 57 percent after 10 to 12 weeks of use.

In a 12-week study comparing SA with BPO, a 2 percent SA cream was shown to be superior to a 5 percent BPO cream in reducing closed comedones, open comedones, inflammatory lesions and total lesions.
Cosmetic approaches for treating acne include the use of antimicrobial agents and oil-control ingredients to reduce sebum. It is estimated that a 30 to 50 percent reduction in sebum will reduce acne by as much as 50 percent.

Numerous cosmetic agents have been shown to be effective oil-control agents. A formulation containing 2 percent niacinamide was reported to reduce sebum by 30 percent after four weeks of use. Another published study evaluated a 4 percent niacinamide gel against a 1 percent clindamycin gel (a topical antibiotic) in patients with moderate acne. After eight weeks, 82 percent of patients treated with niacinamide and 68 percent of those treated with clindamycin were considered improved.

An emulsion containing 3 percent green tea polyphenols (epigallocatechin-3-gallate) reduced sebum by 35 percent after four weeks and 55 percent after eight weeks. In another study, a cream containing 2 percent green tea polyphenols was shown to be an effective anti-acne treatment. Green tea polyphenols may also have antimicrobial, anti-inflammatory and antioxidant activities that significantly contribute to its anti-acne efficacy.

Another cosmetic strategy is to utilize ingredients that have significant activity against P. acnes. The following cosmetic ingredients have been reported in the literature as all having minimum inhibition concentration values (<10 ppm) against P. acnes: phytosphingosine, hinokitiol, hexahydro beta acids (hops), pentadecanol, totarol, phloretin, farnesol and green tea polyphenols. The above-mentioned oil-control and cosmetic antimicrobials can be combined with monographed actives to boost performance. The watch-out is that you cannot make anti-acne claims using only cosmetic ingredients without including an over-the-counter active.