When science is confronted by complex tasks and simpler ones, it is often the simpler tasks that get done first. One only has to look at the currently large number of air contaminant exposure limit criteria and compare that to the virtual absence of quantifiable skin exposure guidance to appreciate this statement. Early occupational health professionals did recognize that many workers were being poisoned as a consequence of getting chemicals on their skin and that guidance for limiting such exposures was needed. However, because detailed guidance was precluded by a lack of measurement techniques, so was the ability to relate the risk of skin exposures to chemicals in a quantifiable manner. Attention focused instead on inhalation hazards, also a problem, and the development of air-sampling techniques to which quantitative analytical methods could be applied. With these air-sampling methods in hand and the ability to quantify exposures, establishing acceptable concentrations based on toxicological data and empirical workplace exposure outcomes was a natural progression. In 1940, the Subcommittee on Threshold Limits was founded at the third annual meeting of the National Conference of Governmental Industrial Hygienists in Bethesda Maryland (ACGIH, 1984). The skin notation was first used by the American Conference of Governmental Industrial Hygienists (ACGIH®) in 1961 to indicate that a 'liquid compound can penetrate the unbroken skin to cause systemic effects' (ACGIH, 1984).