However, there are few epidemiologic studies of exposure to insecticides and allergic contact dermatitis, and studies conducted to date have focused on a variety of insecticides and have involved small study populations.
The committee concludes, from its assessment of the epidemiologic literature, that there is limited/suggestive evidence of an association between exposure to some of the insecticides under review and allergic contact dermatitis that results from sensitization to the compounds and subsequent reexposure.
There is inadequate/insufficient evidence to determine whether an association exists between exposure to the insecticides under review and chronic irritant contact dermatitis after cessation of exposure.
Many solvents are irritants to the skin and cause acute dermatitis. Solvents alter the chemical and physical barriers of the epidermis, remove the lipid film on the surface and thus diminish the protective capacity of the skin. Acute dermatitis can occur after a single exposure or as a cumulative effect after repeated insults by low-grade irritants over a long period. Dryness and cracking of the skin are often the initial features of irritant contact dermatitis with redness, scaling, papules, vesicles and a gradual thickening of the skin developing over time. Irritant contact dermatitis can persist if untreated soon after the initial appearance. Even when the dermatitis appears to be healed, the protective capacity of the skin is still impaired for a period (Andersen, 1986).
Numerous case reports and case series have been included in the medical literature regarding allergic contact dermatitis and exposure to propylene glycol, a solvent widely used in foods, drugs, and cosmetics. Patch testing, used to confirm the diagnosis of allergic contact dermatitis, may have positive results for only a fraction of study participants because not everyone is sensitized to the compound. It has been noted that, because many solvents are irritants, it is difficult to test their potential for allerginicity with standard patch-test techniques (Wahlberg and Adams, 1999).
Using 100% propylene glycol, Andersen and Storrs (1982) patch-tested 84 dermatitis patients and reported that five of 12 patch-test-positive patients had allergic reactions; seven had irritant reactions. In followup tests, 248 eczema patients were patch-tested with propylene glycol at 100%, 20%, and 2% concentrations. Two of five patients with positive reactions to the patch tests developed an eczematous eruption after oral provocation with 15 mL of propylene glycol, confirming its potential as a sensitizer. The authors state that positive patch test reactions to propylene glycol are difficult to interpret and that allergic reactions can be confirmed by clinical relevance, repeated local skin provocation, or oral provocation.
Angelini and Meneghini (1981) conducted patch testing on 400 subjects with 20% propylene glycol in water and six of them developed an allergic contact dermatitis. Hannuksela and colleagues (1975) subjected 1556 eczema patients to a chamber test with propylene glycol, ethylene glycol, and polyethylene glycol. They reported 12.5% positive