Essential Guide azelaic acid

Applications / Skin prone to acne

Benzoyl peroxide Probably the most frequently used anti-acne ingredient is benzoyl peroxide. It has outspoken anti-bacterial properties, but the disadvantage is its total lack of selectivity. Bacteria present on the skin and in the hair follicle are completely eliminated. This includes also P.acnes, the organism that is held responsible for the development of acne. Thus, it prevents acne from progressing.

Commercially available products may contain up to 10% benzoyl peroxide, while a minimum concentration required to combat acne is generally considered to be approximately 2.5%. The absolute amount of benzoyl peroxide applied depends on the severity of the acne outbreak and on the degree of skin irritation induced by the substance. Skin irritation is observed more frequently in certain skin types. Classification based on racial or ethnic background, however, is not a reliable approach. A functional skin type classification provides a more accurate description of skin behaviour. Prof. Proserpio distinguished five different skin types, which better reflect the actual situation:

Dry skin Sensitive skin Mature skin with wrinkles Oily skin Oily skin with enlarged pores

Benzoyl peroxide, like all organic peroxides, is chemically unstable. The bond energy of the –O–O bond is relatively low (approximately 29 kcal per mole). Thermal bond cleavage occurs readily, leading to the formation of two benzoyl radicals. A multitude of subsequent reactions may occur as a result. These benzoyl radicals are highly reactive and act without selectivity. They can react directly with the cell walls of bacteria, moulds and yeasts, but also affect the commensal micro-organisms living on the skin in symbiosis with the human host. Due to their high reactivity, interactions with skin tissue and accessible subcutaneous tissue may also occur. The damage caused by these radical reactions can be significant and is associated with irritation, sensitisation and cytotoxic effects. In addition, benzoyl radicals may undergo decarboxylation, resulting in the formation of phenyl radicals. These phenyl radicals may abstract hydrogen atoms from suitable substrates, leading to the formation of benzene. Benzene is classified as a substance of concern due to its carcinogenic, mutagenic and reprotoxic properties and is therefore undesirable in personal care applications. Within the European Union, benzoyl peroxide is subject to strict regulatory control. Under Regulation (EC) No 1223/2009, its use in cosmetic products is restricted and permitted only under defined conditions following a safety assessment. As a consequence, products containing benzoyl peroxide intended for the treatment of acne are often regulated as medicinal products rather than cosmetic products. In contrast, the legal situation in the United States differs. Benzoyl peroxide is currently permitted in over-the counter anti-acne products, although its safety profile continues to be evaluated by regulatory authorities.

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