Plasters are solid preparations for external application of such consistency as to adhere to the skin and thereby keep a dressing in position. They are amongst the oldest class of pharmaceutical preparations.
Plasters are used to afford protection or mechanical support, and to furnish an occlusive and macerating action. They also bring medicament into close contact with the surface of the skin.
Adhesive plasters consist of vinyl resin, plasticizer and other chemical additives. Such elastic-plastic adhesives are easy to apply, afford dermal protection and are easily cleaned by washing with ordinary soaps and water after soiling.
Two medicated plasters still used are Corn Plaster and Medicated Back Plaster. Back plasters contain oleoresin of capsicum as the active ingredient and are made of a heavy cotton or wool and cotton backing which provides warmth and support.