* Percutaneous: This word literally means "through the skin" and is often used in medical contexts.
* Cutaneous: This word refers to the skin itself.
* Topical: This word refers to the application of a substance to the surface of the skin.
* Dermal: This word specifically refers to the dermis, the inner layer of skin.
While these words all relate to the skin, "transdermal" specifically emphasizes that a substance is absorbed through the skin and into the bloodstream.