**Question:** Following is a type of physical urticaria –

A. Cold Urticaria
B. Heat Urticaria
C. Pressure Urticaria
D. Exercise Urticaria

**Correct Answer:** C. Pressure Urticaria

**Core Concept:**
Urticaria is a skin condition characterized by the appearance of red, itchy wheals (swollen, raised welts) on the skin. There are two main types of urticaria:

1. **Chemical Urticaria:** caused by substances that trigger an allergic reaction in the body, such as certain medications, foods, or environmental allergens.
2. **Physical Urticaria:** caused by physical stimuli that trigger an allergic reaction or direct tissue damage, leading to the release of histamine and other mediators that cause the characteristic symptoms of urticaria.

**Why the Correct Answer is Right:**

C. Pressure Urticaria is a type of physical urticaria. It occurs when a direct mechanical pressure is applied to the skin, causing the release of histamine and other mediators from mast cells and basophils. This leads to the formation of wheals (hives) and itching on the skin, which resolves when the pressure is released.

**Why Each Wrong Option is Incorrect:**

A. Cold Urticaria (option A) is a type of physical urticaria triggered by exposure to cold temperatures. Cold urticaria is different from pressure urticaria as it is not caused by mechanical pressure but by the direct exposure to cold.

B. Heat Urticaria (option B) is another type of physical urticaria triggered by exposure to heat, usually warmth. Heat urticaria is distinct from pressure urticaria, which is caused by mechanical pressure rather than heat.

D. Exercise Urticaria (option D) is a type of physical urticaria triggered by physical exertion or intense physical activity. Exercise urticaria is different from pressure urticaria, which is caused by mechanical pressure applied to the skin.

**Clinical Pearl:**

Pressure urticaria is an important concept to understand as it can manifest in various clinical scenarios, such as:

1. When a patient with pressure urticaria is lying in bed for an extended period (e.g., during surgery or anesthesia)
2. In patients wearing tight clothing or clothes that restrict blood flow to a specific area, leading to the development of pressure urticaria
3. When a patient is seated or lying in a fixed position for an extended period of time, such as in airplane travel or sitting in a wheelchair

**Explanation of the Core Concept:**

Pressure urticaria occurs due to the mechanical pressure applied to the skin, which triggers histamine release from mast cells and basophils. Histamine is a key mediator in the pathogenesis of urticaria, leading to increased vascular permeability, inflammation, and the formation of wheals (hives) on the skin.

**Why the Wrong Options are Incorrect:**

A. Cold Urticaria (option A) is triggered by cold temperatures, not mechanical pressure on