It is not easy to come up with a balanced, objective view on potential toxicity of skin care ingredients. Mainstream skin care companies usually assert that whatever ingredients they use are safe. On the other hand, alternative all-natural skin care outfits profess gloom and doom from synthetic ingredients. The majority of independent studies of the subject focus on acute toxicity of high doses/concentrations rather than a chronic low-level damage from long-term use of small amounts (a situation far more common in real life). Below we discuss some considerations regarding potential harm from skin care ingredients as well as a some possible offenders.
Systemic toxicity
In regard to a topically applied ingredient, systemic toxicity means that it gets into the bloodstream, travels throughout the body and causes damage in organs other than the skin. It does not appear that any of the common over-the-counter skin care products produce systemic toxicity. However, some topical prescriptions drugs, such as hormonal creams, may have systemic toxicity - check with the prescribing physician.
Natural vs. synthetic
Proponents of all-natural skin care believe that any natural substance is more effective that its synthetic analog, and that all synthetic chemicals are toxic. The reality is more complex than that. According to modern science, biological effects of a particular chemical are the same whether it is isolated from natural sources or synthesized in the lab. In theory, that is always true. In reality, depending on whether a substance was derived from natural source or synthesized it may contain different contaminants. Generally, harmful contaminants are more likely in synthetic chemicals, but they do sometimes occur in natural substances as well. In that light, using only natural ingredients reduces but does not eliminate the risk of toxic contaminants -- the integrity and quality standards of the manufacturer are equally important. Also, keep in mind that all-natural products tend to degrade and spoil more easily.
Some synthetic substances have no natural analogs or cannot be isolated from natural sources. These agents are a mixed blessing. Some may have harmful effects on the skin, while others may have positive effects that are far stronger than those of natural agents.
The bottom line is that one should decide between natural and synthetic on a case-by-case basis. For example, natural vitamin E is more effective since is contains only the more effective D form, while the synthetic one is a mixture of D and L. On the other hand, a well known anti-wrinkle agent tretinoin (in Retin A, Renova) is available only in synthetic form, so if you stick to natural formulas, you forego the option of using it.
Low level skin damage
Few, if any, common OTC skin care products contain ingredients that cause immediately obvious skin damage (except in particularly sensitive people). However, the situation is far less clear with low grade irritation, dehydration and other mild damage that may accelerate skin aging in the long run. Unfortunately, many skin care ingredients have not been studies in that context. Therefore, the total effect of a skin care product often is a balance between the benefits from active ingredients and potential low level damage from preservatives, stabilizers, surfactants, synthetic fragrances and other inactives. Sometimes it is impossible to say whether the net effect is worth it. There are two complimentary strategies to deal with this dilemma. First, learn more about the ingredients, both active and inactive -- the more you know the better chance you have to pick an overall beneficial product. Second, you can relatively easily make your skin care yourself (see DIY Antiaging Skin Care Infopack). You may not get the complete control over all ingredients but should be able to eliminate synthetic colors, fragrances, and reduce the need for preservatives and stabilizers.
Ingredients you may want to avoid
Here we list a few ingredients which may be capable of causing skin damage with prolonged use, or are simply redundant.
Imidazolidinyl Urea and Diazolidinyl Urea: Used as preservatives to prevent bacterial growth although ineffective against fungi. Known to be a relatively common cause of contact dermatitis. Two trade names for these chemicals are Germall II and Germall 115. Germall 115 may release formaldehyde, a potentially toxic chemical. Potential for low level skin damage in the long term is unproven but appears likely.
Sodium Lauryl Sulfate: A detergent common in shamoos and cleaners, where it is relatively safe due to short contact time. If exposure is prolonged is likely to cause skin irritation, dryness and other damage. In fact, sodium lauryl sulfate is sometimes used as a model skin irritant in the experiments where skin protectors are tested. Avoid products with sodium lauryl sulfate unless time of contact with the skin is very short. Even skin cleansers should rather be without it.
Mineral oil: petroleum derived hydrocarbons; used as inexpensive base in some products (less today that in the past). Is moderately comedogenic. Mineral oil may also interfere with normal perspiration and other skin functions.
Synthetic Colors: Whether synthetic colors are completely safe or mildly damaging in the long run is unknown. Since they serve no useful purpose, they are best avoided (except perhaps when avoiding them means foregoing an otherwise great product). They are labeled as FD&C or D&C, followed by a color and a number, e.g. FD&C Red No. 6 or D&C Green No. 6.
Synthetic Fragrances: There are over 200 synthetic fragrances used in cosmetics. There is no way to know which particular ones are in your product, since on the label it will simply say "Fragrance." Safety of most synthetic fragrances is an open question. Best to avoid them since they provide no skin benefits. True, it is good to have a nice smelling cream. However, apart from the questionable safety, frangrance may mask spoilage of your product, an effect you would want to avoid.
Ethanolamines (Monoethanolamine aka MEA, Diethanolamine aka DEA, Triethanolamine aka TEA): common pH stabilizers; when exposed to oxygen/air form nitrosoamines, which may be irritating and/or toxic. The amount of nitrosoamines formed during typical use of skin care products with ethanolamines is unclear.
Parabens (e.g. Methyl, Ethyl, Propyl and Butyl Paraben): Used as preservatives; inhibit microbial growth and extend shelf life of products. Methyl paraben may degrade releasing methanol, a potentially toxic chemical. However, the amounts of methanol that might be released from methyl paraben in skin care products are too small for any known systemic effects. Most people don't have an obvious skin reaction to parabens. However, more research is needed to determine whether they are truly nontoxic or may cause low level skin damage in the long term.
Nanoparticles: Nanoparticles are ultra fine particles that possess certain special properties due to their exceedingly small size. This may include the ability to accumulate in the body, possibly even via topical use, and the ability to trigger potentially harmful chemical reactions. As a result, some experts raise concerns about the use of nanoparticles is skin care and cosmetics. Currently, nanoparticles (such as titanium dioxide and zinc oxide nanoparticles) are most commonly used in sunscreens. For more details see our article on the potential risks associated with nanoparticles in skin care.
