**Core Concept**
The epidermis is the outermost layer of the skin, and its turnover time refers to the time it takes for the skin to renew itself. This process involves the proliferation of keratinocytes in the basal layer, their differentiation, and eventual shedding from the surface. The **epidermal turnover time** is a critical aspect of skin physiology.

**Why the Correct Answer is Right**
The normal turnover time of the epidermis is approximately 28 days, which is the time it takes for a keratinocyte to mature and be shed from the skin's surface. This process is essential for maintaining the skin's barrier function and is influenced by various factors, including **growth factors**, **hormones**, and **vitamins**. Understanding this timeframe is crucial in dermatology for assessing skin health and disease.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately reflect the known turnover time of the epidermis.
**Option B:** Similarly, this option does not align with established dermatological knowledge.
**Option D:** This option also does not match the recognized turnover period of the epidermis.

**Clinical Pearl / High-Yield Fact**
Remembering that the epidermal turnover time is about 28 days is crucial for understanding skin regeneration and disease progression. This knowledge can help in managing conditions like **psoriasis**, where the turnover time is significantly reduced.

**Correct Answer:** D. 28 days