**Core Concept**
The Wood's lamp is a diagnostic tool used in dermatology to detect various skin conditions by emitting ultraviolet (UV) light. This specific type of UV light helps to visualize substances that fluoresce, such as fungi, bacteria, and other microorganisms.

**Why the Correct Answer is Right**
The Wood's lamp is used to diagnose conditions like vitiligo, albinism, and certain fungal infections. When a patient's skin is exposed to the UV light, the lamp can highlight areas where there is a lack of melanin, such as in vitiligo, or where there is an overgrowth of microorganisms like in pityriasis versicolor. This is because the UV light causes these substances to fluoresce, revealing their presence.

**Why Each Wrong Option is Incorrect**
* **Option A:** Incorrect because this option is not related to the uses of a Wood's lamp.
* **Option B:** Incorrect because while a Wood's lamp can be used to diagnose fungal infections, it is not the primary purpose of this device.
* **Option C:** Incorrect because a Wood's lamp is not typically used to diagnose conditions like psoriasis, which is usually diagnosed through clinical examination and histopathology.

**Clinical Pearl / High-Yield Fact**
One of the most common uses of a Wood's lamp is to diagnose pityriasis versicolor, a common fungal infection that causes a skin rash. The lamp's UV light helps to reveal the characteristic yellowish or brownish discoloration of the affected skin.

**Correct Answer: D. Diagnosis of fungal infections.**