Many industrialised countries have decreased their occupational exposure limits for a substantial number of chemicals. However, these limits relate to pulmonary exposures only, and decreased concentrations in the inhaled air will not necessarily reduce dermal absorption. In contrast, at a decreased respiratory uptake, the dermal exposure route may gain increased importance.

Skin notations were originally introduced as qualitative indicators of hazards related to dermal absorption. Thus, skin notations were to be used as warning signs only. They therefore need to be supplemented by some kind of quantitative measure to be useful in most practical settings. Further, as a qualitative hazard warning, the skin notation does not allow differentiation between chemicals depending on their toxicity or percutaneous penetration rates. As an indication that skin notations have not been applied as intended, only few new skin notations have been added even when respiratory exposure limit were substantially lowered.

As the understanding of percutaneous absorption processes improved, some countries/organizations developed alternative and more sophisticated guidelines for assigning skin notations to chemicals. These guidelines also aim at taking into account the relative importance of the dermal absorption compared to inhalation at an exposure level equal to the exposure limit. Thus, a skin notation is assigned if dermal absorption is expected to potentially cause a significantly increased total systemic exposure when pulmonary exposure equals the current exposure level. Several issues must be considered. First, how much is a ‘significantly’ increased absorption? Second, should this assessment take into regard that percutaneous absorption may be considerably increased in certain dermatological diseases and after defattening of the skin? Third, many skin exposures involve chemical mixtures where one agent may enhance or attenuate the penetration of another. Should skin notation include substances that enhance the penetration of other, more toxic, chemicals? These issues have not yet been resolved appropriately and may be difficult to address with a simple administrative instrument as a notation in official lists of exposure limits. However, the goal of skin notation remains to serve at least as a warning signal that can lead to appropriate prevention locally.

The different guidelines used for assigning skin notations and the fact that some countries also include skin irritation as a reason for assigning skin notations on chemicals, has lead to a very uneven distribution of skin notations between countries that normally have very comparable exposure limits. A continuing reason for uncertainty is that proper data on dermal penetration of chemicals are very often missing, of questionable quality or only exists for the pure chemical but not for the mixture present in the commercial product. This lack of relevant information on penetration characteristics for sales products has most recently caused authorities to strengthen their requirements for approval of new products. Still, despite the lack of attention to percutaneous absorption in the workplace, the need for skin notation and preventive measures in this regard have only expanded during recent years.

The latest thorough comparison on the use of skin notations on occupational relevant chemicals in different countries dates back some ten years (Grandjean, 1991). We have now attempted to update this information for the purpose of this meeting. The conclusion remains unchanged, that skin notation varies substantially from country to country. Some decisions whether or not to include such notation appear contrary to the evidence. In our view, an improved notation should include a (semi)quantitative measure for assigning skin notations to occupationally relevant chemicals. We propose that the issue of skin notation be taken up by international organizations with the purpose of obtaining an improved tool for preventing hazardous percutaneous uptake of toxic chemicals in the workplace.