Silver is a naturally occurring chemical element (number 47 on the periodic table) with the chemical symbol Ag, which is derived from the Latin word argentum (árgyros in Greek), from the Indo-European root “arg-,” meaning “shining,” “white,” or “gray.” It has been used for medical purposes since ancient times, with Hippocrates (circa 460-370 BCE) noting the beneficial healing and disease-altering activity of the element.1
In modern times, silver compounds – in metallic, nanocrystalline, and ionic formulations – have exhibited broad antibacterial activity and attracted interest for topical antiseptic use in wound dressings.2 Nanocrystalline silver dressings were introduced commercially as antimicrobial dressings in 1998.3 Silver is now used in dressings, catheters, cleansers, ophthalmic ointments, and myriad other medical products. In 2010 alone, an estimated 15 metric tons of silver were incorporated into medical products worldwide.4 It also is included in personal care products, textiles, and water purification devices. In topical skin preparations, the noble metal is included as colloidal silver (suspension of silver particles in an aqueous base) or nanosilver (as nanoparticles ranging from 1 nm to 100 nm in at least one dimension).5 Silver has been used to treat burns and wounds, but this discussion will be limited to acne, atopic dermatitis, and the anti-inflammatory response.
Topical absorption of silver into the skin depends on the vehicle used, concentration, charge, particle size and shape, substance type (that is, silver salt or a nanoparticle), and the coating (in the case of nanoparticles). Smaller nanometer particles (15 nm in rat skin and 6 nm in human skin) are better able to penetrate the skin than larger particles (102 nm and 198 nm, respectively).6 Similar factors influence the efficacy of colloidal silver, which is the most popular type of formulation used in OTC silver products, with the vehicle, concentration of silver in parts per million, pH, and the length of time of exposure the most important. Silver sulfadiazine 1% cream is the form of silver used most often in topical products. Notably, it has a long record of successful use as a safe and effective treatment to reduce Pseudomonas infection in wounds. Silver sulfadiazine 1% cream is contraindicated for individuals who are allergic to sulfa-containing drugs, as it incorporates a sulfa antibiotic.
For several decades, noble metals including silver have been known to exert anti-inflammatory activity.7-11 In the case of silver, its anti-inflammatory properties appear to be mediated by its influence on the cytokine system. Silver nanoparticles inhibit the activity of interleukin-6 (IL-6), IL-12, IL-1beta, and tumor necrosis factor–alpha (TNF-alpha). This impact on the cytokine system is responsible for the impact of silver in demonstrably alleviating symptoms of rheumatoid arthritis.3
In 2004, Bhol et al. used dinitrochlorobenzene (DNCB) to induce allergic contact dermatitis in a guinea pig model, finding that topical nanocrystalline silver cream dose-dependently decreased erythema and as effectively as topical steroids and immunosuppressants.12 The next year, Bhol and Schechter showed that nanocrystalline silver suppressed allergic contact dermatitis in mice, inhibited TNF-alpha and IL-12 expression, and induced inflammatory cell apoptosis.13
In 2008, Nadworny et al. used a porcine contact dermatitis model to investigate the anti-inflammatory activity of nanocrystalline silver. They found that nanocrystalline silver treatments reduced DNCB-induced erythema and edema, promoted apoptosis in dermal cells, and diminished matrix metalloproteinase (MMP) and proinflammatory cytokine expression.3 The investigators speculated that the lower TNF-alpha observed in the silver-treated animals occurred due to apoptosis of the inflammatory cells.
Silver acts as a bactericidal and anti-inflammatory agent, without generating free radicals, as seen with benzoyl peroxide. Therefore, it is a compelling option for responding to the presence of Propionibacterium acnes. However, silver has not been approved by the Food and Drug Administration for this use. Even though formal acne studies have not been performed with silver sulfadiazine, it has long been used “off-label” for this purpose. As suggested above, the use of silver sulfadiazine for acne is limited by the risk of sulfa allergy. Cosmetic appearance and ease of use also are limiting factors, as silver sulfadiazine preparations are characterized by a thick, white pasty consistency. Other options for use of silver to treat acne include silver-containing cleansers and textiles.
A 2006 study in patients with atopic dermatitis demonstrated that silver-coated textiles could significantly diminish Staphylococcus aureus density after 2 days of wearing, with the effect enduring through the end of 7 days of treatment and then 1 week after removal of the textiles.14 Within 2 weeks, objective and subjective symptoms of atopic dermatitis were significantly enhanced in association with the silver-coated textiles, compared with cotton, without measurable adverse effects. A technology called Padycare incorporates silver into micromesh material (82% polyamide, 18% Lycra) used in clothing and bedding.15 As compared with topical formulations applied directly to the skin, textiles confer certain advantages such as preventing scratching and protecting against irritating substances and allergens. Washing of silver-infused textiles is a possible disadvantage, though, as the amount of silver lost from textiles can range from a 100% loss after four washings to less than a 1% loss.16 It also is important to note that there are concerns regarding the potential of silver to leak from textiles into the water supply, and eradicating the beneficial bacteria used to treat the water.
Despite centuries of medical use, silver has not been approved by the FDA for any medical applications. Further study, particularly in terms of safety and efficacy, is necessary. Nevertheless, it is used off-label before and after minimally invasive dermatologic procedures (for example, dermal filling, botulinum toxin injections, chemical peeling) because of its antimicrobial and anti-inflammatory activities as well as soothing qualities for facial skin and the skin barrier. Silver appears to be particularly suitable for use as an acne therapy option due to the low risk of bacterial resistance, lack of irritation, and its preservation of the skin barrier unlike harsher options such as retinoids, antibiotics, and benzoyl peroxide.
Dr. Baumann is chief executive officer of the Baumann Cosmetic & Research Institute in the Design District in Miami. She founded the Cosmetic Dermatology Center at the University of Miami in 1997. Dr. Baumann wrote the textbook “Cosmetic Dermatology: Principles and Practice” (New York: McGraw-Hill, 2002), and a book for consumers, “The Skin Type Solution” (New York: Bantam Dell, 2006). Her latest book, “Cosmeceuticals and Cosmetic Ingredients,” was published in November 2014. Dr. Baumann has received funding for clinical grants from Allergan, Aveeno, Avon, Evolus, Galderma, GlaxoSmithKline, Kythera Biopharmaceuticals, Mary Kay, Medicis, Neutrogena, Philosophy, Topix, and Unilever. Dr. Baumann also developed and owns the Baumann Skin Type Solution skin typing systems and related products.