**Core Concept**
Dermatophytes are a type of fungi that infect the skin, hair, and nails, causing conditions such as tinea corporis, tinea capitis, and onychomycosis. These fungi obtain their nutrients by breaking down keratin, a protein found in the skin, hair, and nails.

**Why the Correct Answer is Right**
The correct answer involves the enzymatic degradation of keratin by dermatophytes. Dermatophytes produce keratinases, enzymes that break down keratin into smaller peptides and amino acids, which are then absorbed by the fungi. This process allows the fungi to obtain the necessary nutrients for growth and proliferation.

**Why Each Wrong Option is Incorrect**

**Option A:** This option is incorrect because it does not accurately describe the role of dermatophytes in keratin degradation.
**Option B:** This option is incorrect because it is not related to the primary mechanism of action of dermatophytes.
**Option C:** This option is incorrect because it is a characteristic of a different type of fungi, not dermatophytes.

**Clinical Pearl / High-Yield Fact**
It's essential to note that dermatophytes can be classified into three main genera: Trichophyton, Microsporum, and Epidermophyton. Each genus has distinct characteristics and can cause different types of infections.

**Correct Answer: D. Keratin degradation by keratinases.**