What skin lesion is characterized by a "herald patch"?

The term "herald patch" is specifically associated with pityriasis rosea, which typically presents as a solitary, large, oval, pink patch on the skin, usually found on the trunk. This lesion often appears a week or two before the more widespread rash develops. Following the herald patch, smaller lesions—resembling "droplets" or "Christmas tree" patterns—generally emerge, making it a distinct feature of pityriasis rosea.

In the context of the other conditions listed: psoriasis often features well-defined, scaly plaques but does not present with a herald patch; acne involves follicular occlusion leading to comedones and inflammatory lesions, lacking any herald-like presentation; and dermatitis herpetiformis is characterized by intensely itchy vesicles, particularly on extensor surfaces, but does not feature a herald patch either. Thus, the presence of a herald patch is a key diagnostic criterion that confirms pityriasis rosea as the correct choice.