Final answer:
Pityriasis rosea is a skin rash characterized by an initial herald patch and a later widespread rash in a 'Christmas tree' distribution, often accompanied by mild itching, and usually resolves without treatment within 6 to 8 weeks.
Step-by-step explanation:
Pityriasis rosea is a skin condition characterized by a distinctive rash that typically follows a pattern of a herald patch, followed by a more widespread rash. Clinical features of pityriasis rosea include an initial single round or oval pink patch known as the 'herald patch', which appears on the chest, abdomen, or back. After one to two weeks, a more widespread rash develops, which is composed of numerous smaller patches that have a similar appearance to the herald patch. The rash spreads in a 'Christmas tree' pattern, extending from the trunk to the arms, legs, and sometimes the neck. The clinical features are often accompanied by mild itching but typically resolve without treatment in six to eight weeks.