**Core Concept**
The Triple Response, also known as the Lewis triple response, is a physiological response of the skin to histamine or other vasodilators, characterized by three distinct phases: the flare, the wheal, and the flare-wheal regression. The flare phase is a vasodilatory response that results in the dilation of blood vessels and increased blood flow to the affected area.

**Why the Correct Answer is Right**
The flare phase is mediated by the release of histamine from mast cells, leading to the activation of H1 receptors on blood vessels. This activation causes the smooth muscle surrounding the blood vessels to relax, resulting in vasodilation and increased blood flow to the area. The H1 receptors are responsible for the contraction of endothelial cells, leading to the dilation of arterioles and venules, which produces the characteristic flare response.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the correct mediator or receptor involved in the flare response.
**Option B:** This option is incorrect because it is a different type of receptor that is not primarily involved in the flare response.
**Option C:** This option is incorrect because it is a different type of mediator that is not primarily involved in the flare response.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the Triple Response is a classic example of how histamine affects the skin, and understanding the role of H1 receptors in vasodilation is crucial for diagnosing conditions like allergic reactions and anaphylaxis.

**Correct Answer:** C. H1 receptors