Pityriasis rosea !

Pityriasis rosea is a harmless, self-limited rash that starts with one larger oval patch and is followed by smaller scaly spots on the trunk.

Updated 2026-11-01

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Skin

What it is

An acute, self-limited papulosquamous eruption of the trunk and proximal limbs, typically beginning with a single 'herald patch' and followed one to two weeks later by many smaller oval scaly plaques aligned along skin cleavage lines. It is not considered contagious.

Who gets it

Common worldwide, mostly in adolescents and young adults (roughly 10–35 years), slightly more often in women, with more cases in spring and autumn in temperate climates. In Colombia it is a frequent reason for dermatology and general-practice consultations and is often confused with fungal infection or secondary syphilis.

Causes

Thought to be linked to reactivation of human herpesviruses 6 and 7 (not proven in every case)
Pityriasis rosea-like drug eruptions with some medicines (for example ACE inhibitors, some biologics and vaccines)
Not caused by fungi or bacteria and not sexually transmitted

Risk factors

Age 10–35 years
Recent upper respiratory infection or prodromal illness in some patients
Pregnancy (a more closely watched setting)
Exposure to medicines known to cause similar eruptions

Pathophysiology

A presumed viral trigger, most often linked to HHV-6/HHV-7 reactivation, provokes a T-cell–mediated inflammatory reaction in the epidermis and upper dermis. This produces patches with a fine collarette of scale at the inner edge. Lesions follow the lines of skin tension (Langer lines), which on the back create the classic 'Christmas tree' pattern.

Classification

Classic pityriasis rosea (herald patch plus secondary eruption on the trunk)
Atypical forms: inverse (folds, face, limbs), papular or vesicular (more common in children and darker skin), and forms without a herald patch
Pityriasis rosea-like drug eruption (no herald patch, often more itchy, resolves when the drug is stopped)

Symptoms and signs

Herald patch: one oval pink or salmon plaque, 2–10 cm, with a collarette of fine scale, usually on the trunk
After 1–2 weeks: many smaller oval scaly plaques on the trunk and proximal limbs
Long axis of lesions along skin lines, forming a 'Christmas tree' pattern on the back
Face, palms and soles usually spared
Mild to moderate itch in many patients; sometimes mild malaise, headache or sore throat before the rash
Post-inflammatory hyper- or hypopigmentation in darker skin

Diagnosis

Clinical: Clinical diagnosis based on the herald patch, the collarette of scale and the 'Christmas tree' distribution on the trunk. Ask about new medicines and sexual exposure.
Tests: A non-treponemal test (VDRL or RPR) is advised when there is any risk of syphilis or atypical features; KOH preparation excludes tinea corporis if the herald patch is doubtful. Biopsy only for atypical or persistent cases (nonspecific spongiotic dermatitis).
Imaging: Not needed.

Differential diagnosis

Secondary syphilis (palms and soles, lymphadenopathy, positive serology)
Tinea corporis (active scaly border, positive KOH)
Guttate psoriasis (thicker silvery scale, often after streptococcal pharyngitis)
Pityriasis versicolor
Pityriasis rosea-like drug eruption, nummular eczema and seborrheic dermatitis

Goal of treatment

Reassure the patient that the rash is benign and self-limited, relieve itch, exclude look-alike conditions such as syphilis, and stop any suspect drug.

Treatment

Conservative: Explanation and reassurance; emollients, lukewarm baths and gentle soaps. Most patients need no other treatment.
Medical: Oral antihistamines and mild to moderate topical corticosteroids for itch. Oral aciclovir is sometimes used early in extensive or symptomatic disease; evidence is modest.
Procedure: Narrowband UVB phototherapy may shorten severe, very itchy cases.
Lifestyle: Avoid hot water, rough clothing and sunburn on the rash; withdraw any drug that might be causing a similar eruption.

Complications

Persistent itch and sleep disturbance
Post-inflammatory hyper- or hypopigmentation, especially in darker skin
Possible association with miscarriage or premature birth when it appears early in pregnancy

Prognosis

Excellent. The eruption usually clears without scarring in about 6–8 weeks (sometimes up to 3 months). Recurrence is uncommon.

Test yourself

Think of the answer, then tap the question to see it.

What is the first lesion of pityriasis rosea called?

The herald patch: a single larger oval plaque with a collarette of fine scale.

Which pattern do the secondary lesions form on the back?

A 'Christmas tree' pattern, with lesions aligned along skin cleavage lines.

Which infection must be excluded, and with which test?

Secondary syphilis, with a non-treponemal test (VDRL or RPR), especially if palms and soles are involved.

Which viruses have been linked to pityriasis rosea?

Human herpesviruses 6 and 7 (reactivation).

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Pityriasis rosea (MedlinePlus, US National Library of Medicine, 2026).

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