ABSTRACT
Skin irritation is a deceptively simple phenomenon. The reality however is very different: skin irritation responses range from a variety of sensory effects, through minor degrees of acute reaction, characterized by erythema, or of cumulative irritancy, characterized by erythema and dryness to more profound degrees of response, including burning/corrosion with consequent scar formation. Such matters are fully covered elsewhere (e.g., Chew and Maibach, 2006, as well as in this book), but for the purpose of this chapter, the focus must be on the evaluation of the acute irritant response. This is simply a refl ection of the historic use of the rabbit Draize test (Draize et al., 1944) as the means of identifying those substances that present a skin irritation hazard (EC, 1992; EC, 1998). In this test, a 4-h semi-occlusive treatment with undiluted material, followed by assessments of erythema and edema up to 72 h in three rabbits, has been deployed to discriminate between substances in the following categories:
Causes severe burns Causes burns Irritant
• • •
Mild irritant Not classifi ed
These categories are rather arbitrary; “not classifi ed” means simply not irritant enough to present an acute hazard. In many areas, including in the European Union, there is no separation between the irritant and mild irritant category. The relevance of these classifi cations to real human hazard has been questioned for many years (Phillips et al., 1972; Nixon et al., 1975; Robinson et al., 1998). They have almost no place at all in the assessment of the risk to human health except for the materials which can cause burns (Basketter et al., 2006), where the obvious advice is to avoid any direct skin contact with the neat material. However, for irritant materials, cumulative effects of the formulation rather than the response to a single exposure of an isolated chemicals is overwhelmingly the issue (Hannuksela and Hannuksela, 1995; Hall-Manning et al., 1995).
