## **Core Concept**
The Lewis triple response is a physiological response of the skin to mild damage, such as stroking or scratching, which involves three main reactions: red line, flare, and wheal. This response is primarily mediated by **histamine** released from damaged skin cells and **neurogenic mechanisms** involving substance P and calcitonin gene-related peptide (CGRP) from sensory nerve endings.

## **Why the Correct Answer is Right**
The redness observed in the Lewis triple response, specifically when the skin is scratched with a pointed object, is primarily due to the **flare response**. This flare response is mediated by the release of **substance P** and other neuropeptides (like CGRP) from the sensory nerve endings. These neuropeptides cause **vasodilation** of the local blood vessels, leading to increased blood flow to the area, which manifests as redness.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because, although histamine does play a role in the Lewis triple response, particularly in the formation of the wheal, it is not the primary cause of the redness (flare) response.
- **Option B:** This option is incorrect as it does not directly relate to the mechanism of redness in the Lewis triple response.
- **Option D:** This option is incorrect because it does not accurately describe the primary mechanism for the redness observed.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the Lewis triple response is often used as a bedside test to assess the integrity of **sensory nerve function**. The response is typically absent or diminished in conditions with sensory neuropathy, such as diabetes.

## **Correct Answer:** .