## **Core Concept**
The triple response of the skin, also known as the triple response of Lewis, is a physiological response to stroking or drawing a line on the skin with a firm object. It involves three main reactions: **red line**, **flare**, and **wheal**. The flare response is a key component of this reaction.

## **Why the Correct Answer is Right**
The flare in the triple response is primarily mediated by **histamine** released from damaged skin cells, particularly mast cells. When the skin is stroked or injured, mast cells release histamine, which then acts on nearby blood vessels. Histamine causes **vasodilation** through its action on **H1 receptors** present on the smooth muscle of blood vessels. This vasodilation leads to an increase in blood flow to the area, resulting in the characteristic redness or flare.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because, although acetylcholine is a neurotransmitter involved in various physiological responses, it is not primarily responsible for the flare in the triple response.
- **Option B:** This option is incorrect as it does not directly relate to the mediation of the flare response in the context of the triple response of Lewis.
- **Option D:** This option is incorrect because bradykinin, while involved in inflammation and pain, is not the primary mediator of the flare response.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the **flare response** is an example of **axonal reflex**, where the sensory nerve endings release **substance P** and **calcitonin gene-related peptide (CGRP)**, leading to vasodilation. However, the primary mediator of the flare in the context of the triple response of Lewis is histamine.

## **Correct Answer:** .