Which term describes the method of delivering substances directly through the skin?

The method of delivering substances directly through the skin is best described as "transdermal." While the answer provided is parental, which typically refers to the administration of substances through routes other than the digestive tract (such as intravenous or intramuscular injections), transdermal specifically indicates the delivery of medications through the skin layers, allowing for systemic effects without the need for injections.

Topical refers to medications applied directly to a specific area of the skin without aiming for systemic absorption. Subcutaneous means the administration of substances into the tissue layer between the skin and the muscle, and intradermal specifies injections made just under the surface of the skin. These methods differ from transdermal in their approach to absorption and intended use.