Dermal exposure to chemicals in the workplace: just how important is skin absorption?

Correspondence to: Dr S Semple, Department of Environmental & Occupational Medicine, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK; [email protected] _________________________ T he study of occupational and environmental exposure to chemicals has traditionally focussed on the quantity of dust, aerosol, or vapour inhaled. This has been driven by the high historic prevalence of respiratory illness among those in mining and manufacturing industries. The large proportion of respiratory physicians working in occupational medicine reflects this. Other exposure routes are often overlooked when evaluating the impact of chemicals on health. It is important to remember that in addition to inhalation, chemicals may enter the body by ingestion, by injection, or by uptake through the unbroken skin (dermal absorption). Often dermal exposure is viewed purely in terms of percutaneous uptake of chemicals. There are however three types of chemical-skin interactions, and an understanding of these is required to characterise the nature of any dermal exposure taking place. Firstly, the chemical may pass through the skin and contribute to the systemic load. Alternatively, the chemical can induce local effects ranging from irritation through to burns or degradation of the barrier properties of the skin. Lastly, the chemical can evoke allergic skin reactions through complex immune system responses that can subsequently trigger responses in the skin at both the point of contact and at skin sites remote to the contact. There is also concern that skin contact may cause respiratory sensitisation. In any given exposure scenario there may be interactions between these modes of action. For example, a chemical can irritate the skin surface leading to increased percutaneous penetration of that, or other, chemicals. However, in each case the substance must diffuse through the outer layers of the skin before any adverse effect is possible. This article aims to highlight the importance of the dermal exposure and absorption route in occupational settings, identify some of the factors that influence exposure and absorption, and describe methods currently used for the measurement and assessment of dermal exposure.