Environmental Engineering Reference
In-Depth Information
question (Spiewak 2008). Hints on patch testing with pesticides (concentrations, vehicles)
may be found elsewhere (de Groot 2008; Spiewak 2011).
16.5.5  Photoallergic Contact Dermatitis
Photoallergic contact dermatitis (PhotoACD) is an inflammatory disease that develops in the
skin of sensitized individuals following exposure to sensitizing hapten (“photohapten” in this
case) and the subsequent irradiation of the light. The light supplies the energy necessary for
the conversion of precursors (prohaptens or prehaptens) into the actual sensitizing photohap-
tens or for the initiation of coupling (photobinding) the hapten with an endogenous carrier
protein into a full antigen. Further, pathomechanisms and clinical appearance of the disease
seem the same as in ACD, with the difference that it affects the body sites that are exposed
both to the photohapten and subsequently to the light (Spiewak 2009a). This may sometimes
complicate the diagnosis of PhotoACD, due to the irregular clinical pattern. The photosensi-
tizing pesticide could be tolerated on cloudy days, and the Sun could be tolerated when not
exposed to the photohapten. Thus, the risk of underdiagnosing this disease seems consider-
ably high. Pesticides with documented photohaptenic properties are listed in Table 16.1 .
16.5.6  Urticaria
Urticaria is characterized by the appearance of wheals—the clinical expression of local-
ized vascular edema in the upper dermis caused by dilatation and increased permeability
of the capillaries in response to the eliciting agent. The clinical expression of the reaction
is wheals developing in the site of contact with the provoking chemical (contact urticaria)
or sometimes involving also other body sites (generalized urticaria). The mechanisms
of contact urticaria involve specific immune reactions or nonimmunologic mechanisms
(Bourrain 2006). Pesticides are among the so-called urticants, that is, xenobiotics capable of
provoking urticaria (Table 16.1).
16.5.7  Erythema Multiforme
A characteristic of this entity is a sudden onset of concentric erythematous papules with
two or more concentric rings of slightly differing colors resembling the iris or bull's eye.
Some authors suggest that erythema multiforme (EM) caused by external chemicals is a
variant of ACD; however, taking into account that the etiology of EM remains obscure, it is
hard to make any definite statement on its nature (Meneghini and Angelini 1981).
16.5.8  Erythema Dyschromicum Perstans (Ashy Dermatosis)
This skin disease occurs predominantly in dark-skinned individuals, and is characterized
by the presence of single or multiple ashen macules of variable size and shape. The cause
of the disease remains unknown; however, in a study of 39 farm workers, the disease could
be related to chlorothalonil exposure (Penagos et al. 1996).
16.5.9  Acne
The occupationally related variant of acne is frequently referred to as chloracne, because it is
mainly caused by certain chlorinated cyclic hydrocarbons (not by gaseous form of chlorine).
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