Pityriasis roseahttps://en.wikipedia.org/wiki/Pityriasis_rosea
Pityriasis rosea is a type of skin rash. The lesion begins with a single red and slightly scaly area. This is then followed, days to weeks later, by a rash of many similar but smaller round or oval lesions, mainly on the trunk and upper limbs. It usually lasts less than three months and goes away without treatment. Sometimes malaise or a fever may occur before the start of the rash or itchiness, but often there are few other symptoms.

While the cause is not entirely clear, it is believed to be related to human herpesvirus 6 or human herpesvirus 7. It does not appear to be contagious. Certain medications may result in a similar rash. Diagnosis is based on the symptoms and a biopsy is usually unnecessary.

As a common disease, about 1.3% of people are affected at some point in time. It most often occurs in those between the ages of 10 and 35.

Diagnosis and Treatment
If it persists for more than 1 month, a detailed work-up may be required to differentiate it from other diseases (parapsoriasis, syphilis).

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  • Pityriasis rosea on the back ― Asymptomatic macules and patches, unlike drug eruptions which usually itch.
  • herald patch ― A large scaly patch that starts before the rest of the lesion and is initially mistaken for a fungal infection.
  • Pityriasis rosea on torso ― Most of the lesions are located on the torso because sunlight improves the lesion.
  • If it itches a lot, you may suspect an allergic disease such as nummular eczema.
  • pityriasis rosea or guttate psoriasis
  • Small herald patch.
References Pityriasis Rosea 28846360 
Pityriasis rosea, also known as pityriasis circinata, roseola annulata, and herpes tonsurans maculosus is an acute self-limiting papulosquamous disorder. It is often characterized by an initial herald patch, followed by scaly oval patches within 2 weeks. However, the herald patch is not always present. The scaly oval patches typically distribute in a Christmas-tree pattern on the trunk and proximal extremities. This activity reviews the evaluation and treatment of pityriasis rosea and the importance of the interprofessional team in recognizing and managing patients with this condition.
 Gianotti-Crosti syndrome, pityriasis rosea, asymmetrical periflexural exanthem, unilateral mediothoracic exanthem, eruptive pseudoangiomatosis, and papular-purpuric gloves and socks syndrome: a brief review and arguments for diagnostic criteria 24470919 
 Pityriasis Rosea: Diagnosis and Treatment. 29365241
Pityriasis rosea is a common rash that usually begins with a single patch on the trunk and spreads to cover the trunk and limbs. Diagnosis relies on clinical examination. The initial patch appears red with a raised border and sunken center. The rash typically emerges about two weeks later. Patients may experience fatigue, nausea, headaches, joint pain, swollen lymph nodes, fever, and sore throat alongside the rash. Similar conditions include syphilis, seborrheic dermatitis, eczema, and others. Treatment aims to alleviate symptoms with corticosteroids or antihistamines. Acyclovir may help in some cases. Severe instances may benefit from UV phototherapy. The disease during pregnancy sometimes has been linked to miscarriage.
 Pityriasis rosea in pregnancy: A case series and literature review 35616213 
In most cases, PR does not influence pregnancy or birth outcomes. Analysis of pooled data from our study and from previous studies revealed that the week of pregnancy at onset of PR was inversely associated with an unfavorable outcome (odds ratio [OR] = 0.937; 95 % CI 0.883 to 0.993). In addition, duration of PR (OR = 1.432; 95 % CI 1.129 to 1.827), additional extracutaneous symptoms (OR = 4.112; 95 % CI 1.580 to 10.23), and widespread rash distribution (OR 5.203, 95 % CI 1.702 to 14.89) were directly associated with unfavorable outcome.
 Clinical variants of pityriasis rosea 28685133 
Pityriasis rosea (PR) is a relatively common, self-limited papulo-squamous dermatosis of unknown origin, which mainly appears in adolescents and young adults (10-35 years), slightly more common in females. It has a sudden onset, and in its typical presentation, the eruption is preceeded by a solitary patch termed “herald patch”, mainly located on the trunk. Few days later, a secondary eruption appears, with little pink, oval macules, with a grayish peripheral scaling collarette around them. The secondary lesions adopt a characteristic distribution along the cleavage lines of the trunk, with a configuration of a “Christmas tree”. In most cases, the eruption lasts for 6 to 8 wk. Its incidence has been estimated to be 0.68% of dermatologic patients, varying from 0.39% to 4.8%.