Irritant agents of all kinds, even if caustic or pustulant in
concentrated forms, may be so diluted as to cause simple erythema. Among
chemical agents we have ammonia, lye, caustic acids and salts, iodine,
carbolic acid, the various tar products, kerosene, aniline, chloroform,
ether, formaline, etc. Of thermic irritants may be named solar heat,
fire heat, steam, hot water, hot air, and congelation (chillblains,
freezing) the latter being especially common in the digital region when
salt has been applied to snow or ice. Vegetable irritants include
mustard, capsicum, moulds, euphorbium, rhus, milkwort, the volatile
oils, etc. Among animal irritants must be named cantharides, mylabris,
potato beetle, insect stings, venom of the irritated toad, liquid
discharges from the kidneys or bowels, and discharges from open sores.
Even the escape of tears upon the face will cause erythema.
The _symptoms_ in all such cases will vary with the potency of the
factor and the susceptibility of the skin. Beside the common symptoms
the color and odor of the skin will often yield valuable diagnostic
indications. There is the white of muriatic acid, carbolic acid or zinc
chloride, the black of silver salts or sulphuric acid, the yellow of
iodine, chromium compounds and nitric acid, the well known odors of
ammonia, iodine, chlorine, carbolic acid, tar, essential oils,
chloroform, ether, formaline, kerosene, mustard, etc.
_Treatment_ is that of simple erythema after one has applied the
appropriate antidote to the particular irritant. For the alkalies and
carbolic acid use vinegar, for the acids oxide or carbonate of magnesia,
chalk or lime water, for iodine and chlorine weak alkaline solutions,
for rhus, ammonia or other alkali, or potassium permanganate, and for
insect stings and animal venoms, alkalies or permanganates. The caustic
salts may demand milk, white of egg, or some other albuminous solution.
When no chemical antidote is available, the first step is to wash off
the offending agent, and then treat the erythema.