Callus or skin callosity develops in response to

Options

A. Pressure
B. Irritation
C. Injury
D. All the above.

Answer

### Step-by-Step Solution:

1. **Understanding Callus**: A callus, or skin callosity, is a thickened and hardened area of skin that typically develops in response to friction, pressure, or irritation. It is most commonly found on the feet (especially heels) and hands (near fingers).

2. **Identifying Causes**: The primary cause of callus formation is pressure. When an area of skin is subjected to repeated pressure or friction, the skin responds by thickening to protect itself.

3. **Evaluating Options**:
- **Option 1: Pressure** - This is a correct cause of callus formation.
- **Option 2: Irritation** - While irritation can affect the skin, it does not specifically lead to the formation of calluses.
- **Option 3: Injury** - Injury leads to different skin responses (like scabbing or healing) but does not cause calluses.
- **Option 4: All of the above** - Since irritation and injury do not cause calluses, this option is incorrect.

4. **Conclusion**: The correct answer is **Option 1: Pressure**, as it is the primary factor that leads to the development of calluses.