Erythema is one of the,commonest primary lesions of the skin. It is produced by the dilation of the cutaneous blood vessels. If the dilation is accompanied by increased permeability, redness and oederna of the skin is produced and features of urticaria1 eruption are seen. At times the cutaneous blood vessels are so irritated and damaged, that they permit the whole blood to pass through, as in purpuras (haemorrhagic rashes). Thus, it will be seen that these three lesions, erythema, urticaria and purpura, depend upon the degree of stimulation or damiige to the cutaneous vascular system.
Diaper Rash (Napkin Rash):
In infants it affects the areas of skin covered by the napkin. Lesions consist mainly of simple erythema, though they may become vesicular or even ulcerative. They are situated, most frequently, on the prominences, and may occupy the inner parts of the thighs, ,perineum and genitalia. Usually the flexures are not affected. The causes of napkin rash are wet or soiled napkins, soap left in the napkins after washing, strong ammonical urine and poor general health.