What is the most likely diagnosis for a woman with hypopigmented scaly lesions post-sun exposure?

The most likely diagnosis for a woman presenting with hypopigmented scaly lesions following sun exposure is indeed pityriasis versicolor. This condition, also known as tinea versicolor, is caused by an overgrowth of Malassezia yeast, which normally resides on the skin. When the skin is exposed to sunlight, areas affected by pityriasis versicolor may become lighter than the surrounding skin, leading to the characteristic hypopigmented lesions.

These lesions typically present as fine, scaling macules or patches that may become more apparent after sun exposure, as the unaffected areas of the skin darken while the affected areas do not tan. This differential tanning contributes to the visibility of the hypopigmented patches, particularly following sun exposure.

Chronic plaque psoriasis usually presents with well-demarcated, raised, erythematous plaques covered with silvery scales but typically does not cause hypopigmentation. Discoid eczema is characterized by round, coin-shaped lesions that are often erythematous and scaly, and the lesions can become crusted or oozing, but they do not usually present as hypopigmented areas post-sun exposure. Pityriasis rosea usually manifests as a herald patch followed by a widespread