**Question:** Which of the following structures is affected by dermatophytes:

A. Nails
B. Hair
C. Skin
D. Nails and skin

**Core Concept:** Dermatophytes are fungi that primarily infect keratinized tissues, which include the skin, hair, and nails. They feed on human keratin, a protein found in these structures.

**Why the Correct Answer is Right:** Dermatophytes primarily affect keratinized tissues, particularly the skin, hair, and nails. The correct answer, "Dermatophytes affect nails and skin," reflects this specificity.

**Why Each Wrong Option is Incorrect:**

A. Nails only: While dermatophytes can infect nails, option A is incorrect because they also affect the skin and hair.
B. Hair only: Dermatophytes can infect hair, but option B is incorrect because they also affect the skin and nails.
C. Skin only: Dermatophytes primarily infect keratinized tissues, which includes the skin. However, they also affect hair and nails. Therefore, option C is incorrect.

**Clinical Pearl:** Dermatophytes are part of the normal skin flora and can cause infections in immunocompromised individuals or when the skin barrier is disrupted, such as in psoriasis or athlete's foot.

**Correct Answer:** Dermatophytes affect nails and skin.