Pityriasis versicolor is caused by
**Core Concept**
Pityriasis versicolor is a common skin condition characterized by patches of discoloration on the skin, caused by a superficial fungal infection. It is primarily associated with an overgrowth of yeast-like fungi that normally reside on the skin, particularly on the upper body.
**Why the Correct Answer is Right**
The correct answer is a type of yeast-like fungus that is commonly found on the skin and can cause pityriasis versicolor when it overgrows. This fungus produces enzymes that break down the skin's natural lipids, leading to the characteristic patches of discoloration. The affected skin areas may appear lighter or darker than the surrounding skin, and may be accompanied by scaling or fine scaling.
**Why Each Wrong Option is Incorrect**
**Option A:** Malassezia is the correct answer. Trichophyton is a type of dermatophyte fungus that causes different skin conditions, such as ringworm.
**Option B:** Aspergillus is a type of fungus that causes respiratory infections and allergic reactions, but is not associated with pityriasis versicolor.
**Option C:** Candida is a type of yeast that causes vaginal yeast infections and oral thrush, but is not typically associated with pityriasis versicolor.
**Clinical Pearl / High-Yield Fact**
Malassezia yeast is naturally found on the skin and feeds on the skin's natural oils, so it's essential to maintain good skin hygiene and use gentle cleansers to prevent overgrowth.
**Correct Answer:** A. Malassezia.