**Core Concept**
Hydroquinone is a commonly used depigmenting agent in the treatment of dermatological disorders such as melasma, freckles, and solar lentigines. It works by inhibiting the enzyme tyrosinase, which is involved in the production of melanin.

**Why the Correct Answer is Right**
Hydroquinone selectively targets melanocytes, the cells responsible for melanin production, and decreases the activity of tyrosinase, thereby reducing melanin synthesis. This results in a decrease in skin pigmentation. Hydroquinone is available in various formulations, including creams, lotions, and gels, and is often used in combination with other treatments for optimal results.

**Why Each Wrong Option is Incorrect**
**Option A:** Kojic acid is another depigmenting agent, but it is not the first-line treatment for dermatological disorders. It works by inhibiting the growth of melanocytes and has a broader spectrum of activity, but it is less commonly used than hydroquinone.

**Option B:** Azelaic acid is an antimicrobial agent and has some depigmenting properties, but it is primarily used to treat conditions such as acne and rosacea. Its depigmenting effects are mild compared to hydroquinone.

**Option C:** Tretinoin is a retinoid that promotes cell turnover and has some depigmenting effects, but it is not a primary depigmenting agent. It is often used in combination with other treatments for skin rejuvenation and to prevent the formation of fine lines and wrinkles.

**Clinical Pearl / High-Yield Fact**
When using hydroquinone, it's essential to note that prolonged use can lead to rebound hyperpigmentation, a condition where the skin becomes even darker than before treatment. This can be prevented by using hydroquinone for short periods and taking regular breaks.

**Correct Answer: C. Hydroquinone is a commonly used depigmenting agent in the treatment of dermatological disorders such as melasma, freckles, and solar lentigines. It works by inhibiting the enzyme tyrosinase, which is involved in the production of melanin.