Pityriasis Rosea (Christmas Tree Rash)

What pityriasis rosea looks like

The rash has a recognizable sequence:

1. Herald patch: a single oval patch, usually 2 to 10 cm (1 to 4 inches) across, appears on the chest, belly, back or neck. It is pink or salmon-colored on light skin and gray, dark brown or purple on darker skin, with a fine ring of scale just inside the edge (a "collarette"). It is often mistaken for ringworm.
2. Secondary rash: 1 to 2 weeks later, many smaller oval patches, 0.5 to 2 cm across, appear across the trunk and upper arms and thighs. Their long axis follows the skin's natural lines, so on the back they slope down and outward like the branches of a fir tree.
3. Fading: new patches stop forming after a few weeks, and the rash gradually fades over 6 to 8 weeks.

Other features:

• Itching in about half of people, mild to severe
• The face, palms and soles are usually spared
• Some people feel mildly unwell, tired, or have a headache or sore throat in the days before the rash
• In children and people with darker skin, the rash may be more raised, involve the face or groin, or follow an "inverse" pattern in the armpits and groin

Causes

The exact cause is not proven. The strongest evidence points to reactivation of human herpesvirus 6 and 7, the viruses that cause roseola in babies. Most people catch these viruses in early childhood, and they stay dormant in the body. Pityriasis rosea is not linked to food, allergies, poor hygiene or fungus.

Some medicines and vaccines can cause a similar rash, called a pityriasis rosea-like eruption. Reported triggers include some blood pressure medicines (ACE inhibitors), NSAIDs, some antibiotics and certain vaccines.

Is pityriasis rosea contagious?

It is not considered contagious. Outbreaks in households or schools are uncommon, and there is no need to stay off school or work or avoid contact with others.

Conditions that look similar

Diagnosis

A doctor can usually diagnose pityriasis rosea by looking at the rash and asking how it started. If there is doubt, they may:

• scrape the scale to look for fungus under a microscope (KOH test)
• order a blood test for syphilis, especially if the palms or soles are involved or there is a sexual risk
• take a small skin biopsy if the rash is unusual or lasts more than 3 months

Treatment

Pityriasis rosea goes away by itself. Treatment aims to relieve itch.

• Gentle skin care: use lukewarm water, mild fragrance-free soap or soap substitutes, and apply a fragrance-free moisturizer twice a day.
• Avoid heat and sweat: hot showers, saunas and heavy exercise can make the rash and itch worse.
• Anti-itch options: calamine lotion, a mild over-the-counter hydrocortisone cream for short periods, or an oral antihistamine at night. Follow the label dose.
• Prescription treatments: stronger steroid creams for severe itch. Some doctors prescribe acyclovir early in the illness, which may speed clearing in some studies, though evidence is limited.
• Sunlight or phototherapy: controlled UVB light can reduce itch in severe cases. Natural sun exposure may help, but avoid sunburn.

Pregnancy

Pityriasis rosea in pregnancy, particularly in the first 15 weeks, has been associated with a higher rate of miscarriage in some studies. Pregnant people with this rash should tell their obstetric team, who may consider antiviral treatment and closer monitoring.

Outlook

The rash usually clears within 6 to 8 weeks without scarring. On darker skin, light or dark marks (post-inflammatory pigment change) can remain for several months before fading. About 2 to 3 percent of people get it again.

Frequently asked questions

Why is pityriasis rosea called the Christmas tree rash?

On the back, the oval patches line up along the natural skin lines, which slope downward and outward from the spine. This creates a pattern resembling the drooping branches of a fir tree. The pattern helps doctors recognize the rash.

What triggers pityriasis rosea?

It is most likely triggered by reactivation of human herpesvirus 6 or 7, viruses most people carry from childhood. Why they reactivate is not known. Some medicines and vaccines can cause a similar rash. It is not caused by fungus, allergy, diet or poor hygiene.

How long does pityriasis rosea last?

Most cases clear within 6 to 8 weeks. Some last up to 3 to 5 months. The herald patch usually appears first, the wider rash follows 1 to 2 weeks later, and new patches stop forming after a few weeks. A rash lasting longer than 3 months should be reviewed by a doctor.

Is pityriasis rosea contagious?

No. It is not considered contagious, and you do not need to stay away from school, work or other people. Spread between family members is unusual. If the rash is actually ringworm or syphilis, those are contagious, so get a diagnosis if you are unsure.

Can pityriasis rosea come back?

It usually happens only once in a lifetime. Only about 2 to 3 percent of people have a second episode, typically milder. A rash that keeps coming back is more likely to be psoriasis, eczema or a drug reaction and should be checked by a doctor.