In the Laboratory
Investigating the Stability of Benzoyl Peroxide in Over-the-Counter Acne Medications Marina Canepa Kittredge, Kevin W. Kittredge,* and Melissa S. Sokol Department of Chemistry and Biochemistry, Siena College, Loudonville, NY 12211; *
[email protected] Arlyne M. Sarquis and Laura M. Sennet Center for Chemical Education, Miami University Middletown, Middletown, OH 45042
This experiment is designed to be used with nonmajor, allied health, or chemical technology students and covers many topics including acne formation, properties of water, chemistry of soaps and detergents, and pharmaceutical formulations. This article is based on one of the activities in The Chemistry of Skin Care and Acne and offers an expanded investigation of the stability of benzoyl peroxide solutions (1). Acne Acne vulgaris, usually referred to as acne, is the most common skin disease. Acne lesions are caused by a disease process in the sebaceous follicle. The sebaceous glands are connected to a canal, called a follicle, that contains a fine hair along with cells called keratinocytes. The sebaceous glands make an oily substance called sebum that is the natural moisturizer of skin. The sebum normally empties onto the skin surface through the opening of the follicle, the pore. Acne develops when the hair and the mixture of oil and cells form a plug that prevents sebum from reaching the surface of the skin through the pore. This results in an ideal condition for the growth and activity of bacterium Propionibacterium acne (P. acne) that normally lives on skin. P. acne starts to grow in the plugged follicles causing redness, swelling, and pain (2). Acne is not restricted to any age group. Although we commonly think of acne affecting only teenagers, adults can get acne in their 20s, 30s, and 40s. Infantile acne is a relatively uncommon condition, but there are children with an onset of acne between the age of 6 and 16 months (3). While acne is not a serious health threat, it can have a great impact on the lives of those who have it. This serious impact has been documented for decades. Sulzberger and Zaidems wrote, “there is no single disease which causes more psychic trauma, more maladjustment between parents and children, more general insecurity and feelings of inferiority and greater sums of psychic suffering than does acne vulgaris” (4). Acne Treatment Benzoyl peroxide is the primary topical agent for treatment of acne vulgaris. It is a white, colorless powder commonly used in over 40 products available over-the-counter (OTC) or by prescription and has been used in dermatology since 1905. It is available in solutions with varying strengths. The 2.5% formulation is less irritating than products with 5% and 10% formulations (5). Its bactericidal effects result from oxidizing P. acne proteins in the sebaceous ducts (6), so the benzoyl peroxide must cross the lipid bilayer into aqueous media containing the P. acne proteins. Water would be the ideal solvent since it easily moves through lipid bilayers. Unfortunately, the solubility of
benzoyl peroxide in water is poor and a co‑solvent must be used. Industrially, the most common co‑solvents are propylene glycol, isopropyl myristate, acetone, and alcohol. In these solvents the necessary concentration of benzoyl peroxide can be prepared. In addition to solubility issues, a combination of solvents is also necessary to guarantee a good product shelf life. Benzoyl peroxide degrades in solution at low temperatures (
