**Core Concept**
The question requires the understanding of various substances that can enter the human body through the skin. The skin serves as a primary barrier against external pathogens and substances. However, certain compounds can penetrate the skin through various mechanisms, including diffusion, active transport, or as a result of skin injuries.

**Why the Correct Answer is Right**
While many substances can enter the human body through the skin, there are a few exceptions. Substances like water, oxygen, and carbon dioxide can diffuse through the skin. Additionally, certain medications, such as topical corticosteroids, can be absorbed through the skin. However, one substance that does not enter the human body through the skin is **inhalation anesthetics**. These substances are primarily administered through inhalation, where they are absorbed through the lungs into the bloodstream.

**Why Each Wrong Option is Incorrect**
* **Option B:** While the exact substance is not specified, some inhalation anesthetics, like nitrous oxide, are not absorbed through the skin but rather through inhalation.
* **Option C:** The question does not provide a substance, but typically, substances like oxygen and carbon dioxide can diffuse through the skin.

**Clinical Pearl / High-Yield Fact**
Substances that enter the human body through the skin often do so through mechanisms like diffusion, active transport, or as a result of skin injuries. However, certain substances like inhalation anesthetics are primarily absorbed through the lungs.

**Correct Answer:** D.