**Core Concept:** Pityriasis versicolor is a common fungal infection caused by the yeast Malassezia species, particularly Malassezia sympodialis, Malassezia globosa, and Malassezia furfur. These yeasts are normal inhabitants of the skin but can cause infection under specific conditions.

**Why the Correct Answer is Right:** Pityriasis versicolor is caused by Malassezia species because they are commensal yeast on the skin surface that can cause infection when overgrown due to factors like altered skin pH, immunosuppression, or increased skin surface area. The characteristic whitish-yellow, umbilicated, and scaly lesions occur due to the destruction of melanocytes, leading to hypopigmentation or hyperpigmentation.

**Why Each Wrong Option is Incorrect:**

A. Malassezia species is a correct answer, but the correct answer should be "Malassezia species", not specifying a particular species.

B. This option is incorrect as the infection is caused by Malassezia species, not by dermatophytes (fungi causing ringworm).

C. This answer is incorrect as the infection is caused by Malassezia species, not by bacteria like Staphylococcus and Streptococcus.

D. This option is incorrect as the infection is caused by Malassezia species, not by viruses like Herpes simplex virus or Epstein-Barr virus.

**Clinical Pearl:** Pityriasis versicolor is an important differential diagnosis to consider in patients with hypopigmented or hyperpigmented macules and patches, as it can be confused with other skin conditions like vitiligo or melasma. Early diagnosis and treatment are crucial to prevent complications like scarring or exacerbation of the condition.

**Correct Answer:** Malassezia species