**Core Concept**
Trichophyton, Microsporum, and Epidermophyton are dermatophyte fungi that infect the hair, skin, and nails in humans, respectively. These organisms are responsible for various fungal infections, including tinea capitis (scalp infection), tinea corporis (body infection), and tinea unguium (nail infection).

**Why the Correct Answer is Right**
Epidermophyton is the organism that primarily infects the skin and nails but does not infect hair. This is because Epidermophyton species, such as Epidermophyton floccosum, lack the enzymes required to break down keratin, a key component of hair.

**Why Each Wrong Option is Incorrect**
**Option A:** Trichophyton, including species like Trichophyton tonsurans, is a common cause of tinea capitis, which affects the hair. Therefore, Trichophyton does infect hair.
**Option B:** Microsporum, such as Microsporum canis, is another dermatophyte that infects the hair, leading to conditions like ringworm of the scalp. Thus, Microsporum also infects hair.
**Option C:** While the question does not provide a specific organism, it is likely intended to test knowledge of the dermatophytes. In that case, none of the options provided (A, B, or C) are correct. However, if we assume a common dermatophyte, we can still conclude that the correct answer is not among the options provided.

**Clinical Pearl / High-Yield Fact**
When diagnosing fungal infections, it is essential to consider the patient's symptoms, medical history, and geographic location. For example, Trichophyton tonsurans is commonly found in the United States and is a leading cause of tinea capitis in children.

**Correct Answer:** D.