**Core Concept**
Superficial thrombophlebitis refers to the inflammation of a vein just beneath the skin, typically caused by a blood clot (thrombus) that forms within the vein. This condition is often associated with trauma, infection, or other local irritants that disrupt the normal flow of blood.

**Why the Correct Answer is Right**
The most common cause of superficial thrombophlebitis is injury to the vein, which can lead to activation of the coagulation cascade and subsequent thrombus formation. This injury can be caused by various factors, including intravenous catheters, injections, or even tight clothing that constricts the vein. The resulting thrombus can cause inflammation and pain in the affected area.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while infection can cause superficial thrombophlebitis, it is not the most common cause.
**Option B:** This option is incorrect because while certain medications can increase the risk of thrombophlebitis, they are not the most common cause of superficial thrombophlebitis.
**Option C:** This option is incorrect because while deep vein thrombosis is a more serious condition, it typically occurs in deeper veins and is not the most common cause of superficial thrombophlebitis.

**Clinical Pearl / High-Yield Fact**
It's essential to recognize that superficial thrombophlebitis can be a sign of an underlying condition, such as a blood clot or infection, which may require prompt medical attention. Therefore, if you suspect superficial thrombophlebitis, it's crucial to investigate the underlying cause and provide appropriate treatment.

**Correct Answer:** C. Tight clothing