**Core Concept**
Solar urticaria is a rare type of physical urticaria, characterized by the development of wheals (hives) following exposure to sunlight. This condition is an immune-mediated response to sunlight, leading to the release of histamine and other mediators from mast cells.

**Why the Correct Answer is Right**
In solar urticaria, the skin reacts to sunlight by releasing histamine and other chemical mediators from mast cells, leading to increased blood flow and permeability. This results in the formation of wheals, which are itchy, raised areas of skin that can appear anywhere on the body. The wheals are a hallmark of solar urticaria and distinguish this condition from other types of sun-induced skin reactions.

**Why Each Wrong Option is Incorrect**
**Option A:** Stinging is not a characteristic feature of solar urticaria, although some patients may experience pruritus (itching).
**Option B:** Erythema (redness) can occur in solar urticaria, but it is not the defining feature of this condition.
**Option D:** Loss of sensation is not a typical feature of solar urticaria, and patients often experience itching and discomfort.

**Clinical Pearl / High-Yield Fact**
Solar urticaria is a rare but important condition to recognize, as it can be a sign of underlying immune system dysfunction. Patients with solar urticaria may also be more susceptible to other types of physical urticarias, such as cold urticaria or cholinergic urticaria.

✓ Correct Answer: C. Wheal formation