**Core Concept**
The use of a Wood's lamp in dermatology and dentistry to diagnose conditions that cause fluorescence is based on the principle of ultraviolet (UV) light interaction with certain chemicals or pigments in the skin or oral mucosa. The Wood's lamp emits UV light, which excites certain molecules, causing them to emit a characteristic color, often yellow or green.

**Why the Correct Answer is Right**
Tinea versicolor is a common fungal infection caused by Malassezia species, which is naturally present on the skin and mucous membranes. The infection leads to the production of porphyrins, which are fluorescent molecules that absorb UV light and emit a yellow fluorescence when excited by the Wood's lamp. This characteristic fluorescence is a diagnostic hallmark of tinea versicolor. The fungus Malassezia feeds on the oils produced by the skin, leading to an overgrowth and the characteristic skin lesions.

**Why Each Wrong Option is Incorrect**
**Option A:** Tuberous sclerosis is a genetic disorder characterized by the growth of non-cancerous tumors in various parts of the body, including the skin and brain. While it does have skin manifestations, such as ash-leaf spots and shagreen patches, it does not cause fluorescence on a Wood's lamp.

**Option B:** Pseudomonas infection is caused by the bacterium Pseudomonas aeruginosa, which can cause a range of infections, including skin and soft tissue infections. However, it does not cause fluorescence on a Wood's lamp.

**Option D:** Erythrasma is a fungal infection caused by Corynebacterium minutissimum, which affects the skin folds, such as the groin and axillae. While it can cause skin discoloration, it does not cause fluorescence on a Wood's lamp.

**Clinical Pearl / High-Yield Fact**
When using a Wood's lamp for diagnostic purposes, it is essential to note that the fluorescence may fade over time, and the results may not be immediately reproducible. Additionally, the Wood's lamp can be used to diagnose other conditions, such as vitiligo, which shows a characteristic blue fluorescence.

**✓ Correct Answer: C. Tinea versicolor**