Silver (nano)particles are used due to their antimicrobial effects (mainly against bacteria and fungi, less against viruses) in different consumer goods and medical products, e.g. in textiles, for wound treatment (including skin burns) or for skin diseases such as neurodermatitis. Here the main task of silver is to protect the skin surface against excessive bacterial colonisation by releasing silver ions. At the same time this also means that in case of wound treatment the silver ions or particles can penetrate into deeper tissue areas of the skin.

Mandatory Nano labelling in cosmetics, biocides and food

The European Parliament has reacted to the recent fear that very small particles may penetrate the skin and exert toxic effects by changing the EU Cosmetics Directive. It stipulates that since July 2013 all nanoparticles contained in cosmetics must be labelled with the term "(nano)" as indicated on the list of ingredients.

First-aid box and wound dressing © Olivier DIRSON / fotolia.com; © vladans / fotolia.com

 

For medical wound care, especially for skin burns, there are already several products on the market that are equipped with silver and/or silver nanoparticles. In case of silver-coated wound dressing material that was applied to damaged skin the integrated 15 nm silver nanoparticles were absorbed into the skin from this product. After one week of local treatment increased quantities of silver could be detected in the plasma and the urine of the patient without adversely affecting the health of the patient. Compared to healthy skin silver nanoparticles can penetrate much deeper into damage skin. Combining nano silver with nanocellulose results in improved wound dressing materials that were demonstrated in in vitro and in vivo experiments to exhibit a similar or even improved antimicrobial activity (compared to conventional products) combined with an accelerated wound healing and lower toxicity.[1,4,6-8,10,12]

 

Marathon runners with functional clothing. © Kara / fotolia.deIn the textile sector there are different ways to apply silver nanoparticles, with their antimicrobial effect, to the fibres. Solidly incorporated silver is not lost during washing processes allowing for a controlled and persistent long-term release of silver ions. Comparative studies with volunteers who were wearing such silver-equipped T-shirts for several weeks displayed no harmful effects to the skin or allergic reactions to the product whilst showing good antimicrobial effects. However after simulating the wearing of nano silver containing sportswear in the laboratory the studies showed that both silver ions and silver nanoparticles were being released into the artificial sweat. A worst case scenario in this simulation would correspond to a non-negligible maximal skin exposure of 8.2 - 17.1 micrograms of silver per kg body weight.[9,5,2]

 

In principle silver nanoparticles can only trigger a systemic toxicity when applied to the skin if they are able to completely penetrate the skin barrier. Various studies in the laboratory (in vitro and in vivo) have tested the penetration potential of silver nanoparticles and have shown that if detectable at all, only a very small proportion of silver ions can pass through the corneal layer (stratum corneum) of the skin. After applying creams and lotions to the skin with an active-agent content (silver) in the range of 0,1 to 1,5 %, less than 0,1 percent of the amount applied was recovered in the in the corneal layer without having penetrated the skin.12,3]

If we now perform a conservative risk assessment based on these data it follows that 10 g cream with a microsilver content of 1 % contain 100 mg silver providing an estimated amount of 10 to 500 μg silver ions. At most 1 % of these silver ions are able to penetrate the deeper layers of the skin which corresponds to 0,1 to 5 μg silver ions. In total, this means in case of a generous estimate for a full body treatment (30 g of cream) 0,3 to 15 μg silver is taken up via the skin.[12]

 

Literature arrow down

  1. Bianco, C et al. (2014). Burns, 40(7): 1390-1396.
  2. Hoefer, D et al. (2011). ISRN Dermatol, 2011 369603.
  3. Kim, JS et al. (2013). Nanotoxicology, 7(5): 953-960.
  4. Larese, FF et al. (2009), Toxicology, 255(1-2): 33-37.
  5. Paladini, F et al. (2014). J Biomed Mater Res B Appl Biomater, 102(5): 1031-1037.
  6. Rigo, C et al. (2012). Burns, 38(8): 1131-1142.
  7. Rigo, C et al. (2013). Int J Mol Sci, 14(3): 4817-4840.
  8. Samberg, ME et al. (2010). Environ Health Perspect, 118(3): 407-413.
  9. Von Goetz, N et al. (2013). Environ Sci Technol, 47(17): 9979-9987.
  10. Wu, J et al. (2014). Biomed Mater, 9(3): 035005.
  11. Daniels, R et al. (Ausgabe 16/2009). "Pharmazeutische Zeitung online: Mikrosilber: Alte Aktivsubstanz in neuem Gewand" (Stand letzter Zugang: Dez 2014)
  12. Wijnhoven, SWP et al. (2009), Nanotoxicology, 3(2): 109-U178

 

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