ABSTRACT
I. INTRODUCTION Unlike our ancestors, we now live in a complex environment full of a variety of synthetic molecules. On a day-to-day basis contact is made with a wide range of compounds and almost everything that comes into contact with the skin has the potential for inducing adverse cutaneous reactions. A brief review of the dermatological journals dealing with contact dermatitis will reveal that someone, somewhere has reacted to something that they have been in contact with for short or long periods of time. Contact dermatitis reactions may be immediate or delayed, chronic or acute, irritant or allergic. An additional cofactor in the development of cutaneous reactions may be ultraviolet radiation (UVR). UVR has the capacity to energize molecules, and in this photoactive state, these molecules can produce phototoxic (photoirritant) and photosensitive (photoallergic) reactions. With topical formulations the cause of adverse reactions may be the vehicle and not the drug itself. Similarly with transdermal delivery systems the adhesives used to produce intimate contact with the skin may be a source of cutaneous reactivity. An additional problem with transdermal delivery systems is that the physical process of removal from the skin can induce mechanical trauma to the skin surface leading to erythema and edema. A further complication may be that the mechanical trauma leads to altered barrier function of the skin which, in turn, could enhance the percutaneous penetration of materials at or near the skin surface. Whatever the mechanism, adverse cutaneous reactions are
a frequent problem with materials that come into contact with the skin. The resulting contact dermatitis can be a source of considerable discomfort and inconvenience and limit the usefulness of a topical formulation or transdermal delivery system.
