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Nanoparticles in skin care: The risks may trump the rewards

Nanotechnology is one of mankind's biggest hopes for technological progress in the 21-st century. It promises to revolutionize manufacturing, materials science, computers, medical devices and much more. Skin care is among the fields where nanotechnology is being enthusiastically introduced.

While scientific progress should generally be welcomed in all industries, introduction of nanotechnology in skin care and cosmetics may require a special degree of caution. Notably, skin care is not regulated by the FDA, partly because skin care products are topical and their systemic effects tend to be small, if any. Hence the FDA does not consider the health risks of skin care to be significant enough to bother to regulate it. This may be sensible considering the FDA's limited budget and its many other responsibilities. However, nanotechnology, particularly nanoparticles, may throw such logic to the wind.

Let me explain. When skin care formulas are applied to the skin, each ingredient usually ends up following one of three scenarios (or a combination thereof):

  • It stays on the surface of the skin without penetrating it. Eventually it is washed off.
  • It penetrates the skin and stays there, never entering the blood circulation in any significant amounts. Eventually it is excreted (e.g. as a part of dead skin cells as they peel off) without having any systemic effect.
  • It enters blood circulation, travels to other organs, undergoes transformations in the liver, and so forth. Eventually it is excreted via urine and bile. This scenario is potentially the most dangerous of the three. However, most ingredients entering systemic circulation via topical use often do so in relatively small amounts, i.e. small enough to be considered posing low risk, if any.

The situation with nanoparticles is potentially quite different. First, a few details. Nanoparticles are exceedingly small clumps/crystals of some substance with size ranging from 1 to 100 nanometers. For reference, one nanometer (one thousandth of a millimeter) is about the width of human DNA whereas 75,000 nanometers is the width of an average human hair. The ultra-small size of nanoparticles has two important consequences.

First, many chemicals behave differently when packaged into nanoparticles. For example, normally inert substances, when turned into nanoparticles, can trigger potentially harmful chemical reactions. An imperfect but well known analogy is asbestos: inert silica is harmless in its common forms but hazardous when converted into asbestos crystals.

Second, many experts believe that some nanoparticles might be able to penetrate the skin and enter systemic circulation under certain conditions. What's worse, commonly used nanoparticles do not dissolve in either water or oil, and, once absorbed, are very difficult for the body to eliminate, which may dramatically increase their long-term risks.

In view of the above, an ingredient proven safe in ordinary form, may still be hazarous in nanoparticles. A case in point is a recent study of the effects of titanium dioxide nanoparticles in mice. (Titanium dioxide is a popular sun-blocking and makeup ingredient whose ordinary formulations are non-toxic.) A team researchers from UCLA led by Dr Schiestl found that mice exposed to titanium dioxide nanoparticles via drinking water started showing genetic damage within five days. The researchers reported that titanium dioxide nanoparticles induced single- and double-strand DNA breaks and also caused chromosomal damage as well as inflammation, all of which increase the risk for cancer.

Dr Schiestl believes that titanium dioxide nanoparticles do not penetrate intact skin and, therefore, should probably be safe in sunscreen lotions while posing risk in sunscreen sprays (due to inadvertent inhalation). However, very little research has been done on the ability of nanoparticles to penetrate human skin in real-life use. The risk of penetration may be greater than commonly thought for a number of reasons. First, nanoparticle range in size from from 1 to 100 nm. The smallest ones may penetrate much more easily than the larger ones. Penetration may be affected by the condition of the skin, including inflammation, lesions, dryness, recent exfoliation, concurrently used products, mechanical stress (e.g. rubbing or scratching) and numerous other factors. Until the penetration of a wide variety of nanoparticles under a variety of real-life conditions has been studied, it is premature to rule out the risks of their topical use. Also, even if only a small fraction of topically applied nanoparticles penetrate the skin, they may pose disproportionately high risk due to their ability to accumulate in the body over time.

So far, only titanium dioxide nanoparticles consumed orally were shown to produce genetic damage. The question of the risks posed by other common types of nanoparticles (e.g. zinc oxide nanoparticles) remains open. It is also unclear whether and under what conditions topical use of nanoparticles might be hazardous. In my view, considering the uncertainly and nascent state of research in this area, it may be prudent to avoid all skin care products with nanoparticles until more studies are available to better estimate the long-term risks.

Bottom line

There is evidence that a normally inert and non-toxic skin care ingredient, titanium dioxide, may produce genetic damage if it enters the body in the form of nanoparticles. Other common substances may pose similar risks when converted to nanoparticles. Some experts believe that nanoparticles do not penetrate into the body when applied topically. However, there is not enough data to rule out some penetration, especially of smaller nanoparticles under predisposing conditions. Considering potential risk of the nanoparticle accumulation in the body, it would be prudent to avoid skin care products with nanoparticles until more studies are available to better estimate the long-term risks.


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