**Question:** Spider nevi are due to action of -
**Correct Answer:** C. Increased estrogen.

**Core Concept**
Spider nevi, also known as spider angiomas, are a type of vascular anomaly characterized by a central red spot with radiating red lines or a spider-like appearance. They are often associated with liver disease, pregnancy, and estrogen therapy. The underlying mechanism involves the abnormal formation of blood vessels.

**Why the Correct Answer is Right**
Increased estrogen levels stimulate the proliferation of endothelial cells, leading to the formation of new blood vessels. This results in the characteristic spider-like appearance of spider nevi. The increased estrogen levels can be due to various factors such as pregnancy, liver disease, or estrogen therapy. The estrogen receptors in the endothelial cells are activated, leading to the expression of vascular endothelial growth factor (VEGF), which promotes angiogenesis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not relate to the pathogenesis of spider nevi.
**Option B:** This option is incorrect as it is not directly related to the formation of spider nevi.

**Clinical Pearl / High-Yield Fact**
Spider nevi are a useful clinical sign of liver disease, particularly in patients with cirrhosis. They are also associated with other conditions such as pregnancy, estrogen therapy, and malignancies.