method of delivery. Microscopically, cutaneous effects begin to appear almost immediately after sulfur mustard contact with skin. Large dosages yield an immediate and profound effect in 1 to 2 hours. Necrosis of the skin following the delivery of large vapor dosages does not appear instantaneously, usually occurring after variable periods of latency. Total necrosis of the skin may occur. Small vapor dosages yield delayed skin effects that may occur 7 to 14 days after exposure. Interestingly, the timing of the onset of sulfur mustard cutaneous reactions is not unlike that observed in cutaneous reactions associated with common Rhus (poison ivy oleoresin) dermatitis.
The precise mechanism whereby increased humidity or increased moisture on the skin potentiates sulfur mustard effect is unknown. However, it is possible to assume that wetting the skin alters the permeability of skin cells, thereby increasing the ability of sulfur mustard to penetrate to metabolically active layers; 5 percent, but not 4 percent, sodium chloride-containing water reduces sulfur mustard effects on the skin. It is postulated that 5 percent sodium chloride decreases the solubility of sulfur mustard in water, decreases the overall rate at which sulfur mustard molecules become activated, or alters sulfur mustard penetrability through skin (Renshaw, 1947).
The mechanism whereby an increase in environmental temperature increases the adverse effect of sulfur mustard is also unknown. Increased environmental temperature may simply increase body temperature, stimulating eccrine sweat gland activity and a concomitant increase in hydration of the skin. It is also possible that profuse sweating and a concomitant increase in the amount of pure water on the skin cause activation of greater quantities of sulfur mustard at the site. Blistering of the skin by exposure to UV light is also enhanced by increased temperature and humidity.
The site of skin exposure and the thickness of skin may often determine the type of cutaneous responses experienced upon exposure to sulfur mustard. Thick skin is purported to be less affected by the irritant effects of sulfur mustard. Likewise, young skin, thought to be morphologically thinner than old skin, and female skin, thought to be thinner and more delicate than male skin, are suspected of reacting more severely at all sites upon a given exposure to sulfur mustard (Mathias, 1987; Renshaw, 1946). Racial factors and skin color appear to have even less well defined relationships. It has been generally accepted that black skin reacts in a different manner than white skin to contact allergens and irritants. Yet there are no good experimental data to support the concept that there are substantial differences in the cutaneous response of black or white skin to antigen and injury. Weigand and colleagues (1974) described a difference between black and white skin in the number of cell layers in the stratum corneum, but these differences