Pityriasis Rosea: Herald Patch, Christmas-Tree Rash and When to Worry

Pityriasis rosea is a common, harmless rash that usually starts with one oval, pink, scaly patch called the herald patch, followed days to weeks later by many smaller oval patches on the chest, back, arms and legs. On the back the small patches often line up along the skin's natural creases, a pattern doctors compare to the branches of a Christmas tree. It is not contagious and clears on its own, usually within 6 to 8 weeks, though it can take a few months.

Pori does not diagnose skin conditions; its selfie scans and photo diary in Pori can help you keep dated, consistent photos to show a dermatologist and see whether treatment is working.

What does pityriasis rosea look like?

The rash has a typical order of events, which is often the best clue.

1. The herald patch. The NHS describes it as usually oval or round, slightly raised and about 2cm to 5cm across. It often has a fine ring of scale just inside its edge and a paler center. Many people mistake it for ringworm.
2. The spread. The NHS says smaller scaly spots appear about 5 to 15 days later, usually on the chest and back. The AAD says the widespread rash can follow a few days to a few weeks after the herald patch.
3. The pattern. MedlinePlus notes that the rash may appear in a Christmas tree pattern. DermNet explains that the oval patches tend to follow the relaxed skin tension lines of the upper body, so on the back their long sides slope down and out from the spine.

The spots often appear on both sides of the body and can itch. In children the NHS says they may also appear on the face or scalp. In adults the face is usually spared, which helps tell it apart from many other rashes. American Family Physician notes that on the upper chest the patches can form a V shape instead. Some people feel unwell first: MedlinePlus lists headache, tiredness, sore throat and mild fever.

What does pityriasis rosea look like on brown and black skin?

The pink color in most textbook photos can be missing on darker skin. The NHS says the herald patch may be darker with a light border, and the smaller spots can be gray, dark brown or black. The scaly edges and the tree-like layout on the back still show.

After the rash clears, darker or lighter patches can remain. The AAD says these are not scars and fade over time, although spots on sun-exposed skin can take months to fade. The NHS adds that they are more noticeable on brown and black skin and usually fade within a few months. Gentle sun protection can help them even out; see our skincare routine for dark skin.

What causes pityriasis rosea, and is it contagious?

Nobody knows the exact cause. The AAD says research suggests a virus, and some people get it after a viral illness. DermNet says the strongest known link is with human herpesviruses 6 and 7, though studies have not confirmed it. These are common childhood viruses and are unrelated to cold sores.

Pityriasis rosea is not contagious and is not a sexually transmitted infection, according to the AAD. MedlinePlus notes that it sometimes shows up in several people in the same household at once, which is one reason a viral trigger is suspected.

Who gets it?

• The AAD says you are most likely to get it between 10 and 35 years of age, though it can happen at any age.
• MedlinePlus says it is seen most often in the fall and spring, and women seem to get it more often than men.
• Most people who get it are otherwise healthy, and many get it only once. DermNet puts recurrence at 1 to 3%.

Can medicines cause a rash that looks like it?

Yes. The AAD notes that some medicines and vaccines can cause a rash that looks like pityriasis rosea, and names terbinafine, naproxen and captopril as examples. If the rash started soon after a new medicine, tell your doctor; stopping or swapping the drug may be the treatment.

What else could it be?

The AAD warns that the rash can look like ringworm, psoriasis or eczema, which often need treatment. DermNet and American Family Physician add secondary syphilis, which can cause oval spots on the trunk, palms and soles. This table shows the most common look-alikes.

For rashes that also reach the face, our guide to the common causes of a rash on the face may help.

When should you get tested for other causes?

Doctors usually diagnose pityriasis rosea by looking at it. MedlinePlus says that in rare cases a blood test to rule out syphilis or a skin biopsy is needed. DermNet says other conditions should be considered when the diagnosis is uncertain, especially if the palms or soles are involved, and that blood tests for the herpesviruses are not useful. Ask your doctor about tests if:

• The rash is on your palms or the soles of your feet.
• There was no herald patch, or the rash does not follow the usual pattern.
• You have had a new sexual partner, sores in the mouth or genitals, or swollen glands.
• You started a new medicine or had a vaccine shortly before the rash appeared.
• The rash lasts longer than about 10 weeks. Cleveland Clinic uses 10 weeks as a reason to see a doctor, and the NHS uses 3 months.
• You are pregnant (see below).

How is pityriasis rosea treated?

There is no cure, and the AAD says the rash goes away on its own. Treatment is about comfort while you wait. MedlinePlus says an episode usually lasts 4 to 8 weeks and rarely comes back; DermNet gives 6 to 10 weeks. The NHS says it may get worse before it gets better.

Home care

• Use a plain moisturizer on the rash, as the NHS suggests. Products with colloidal oatmeal can soothe itchy, dry patches.
• Skip harsh soaps and body washes, and take lukewarm rather than hot showers.
• Oral antihistamines can ease itch, especially at night. Ask a pharmacist which one suits you.
• MedlinePlus lists mild hydrocortisone cream for itchy spots. Follow the label.
• Moderate sunlight may help the rash fade faster, according to MedlinePlus, but avoid sunburn.

What a doctor may prescribe

If the itch is bad or the rash is widespread, a doctor may prescribe a stronger steroid cream, and Cleveland Clinic says oral prednisone is sometimes used. DermNet says a short course of the antiviral acyclovir may speed healing and relieve itch in severe cases, and that light therapy (phototherapy) is an option for extensive or persistent rashes. A board-certified dermatologist can confirm the diagnosis and help with lingering dark or light spots.

Is pityriasis rosea dangerous in pregnancy?

Usually the rash itself is harmless, but pregnancy is the exception worth acting on. The NHS says that if you are pregnant and get a new rash, you should contact your midwife, maternity unit or doctor right away, because pityriasis rosea in the first 15 weeks of pregnancy has been linked with miscarriage and premature birth. The AAD notes that studies disagree and that your obstetrician may simply monitor you more closely. Either way, tell them.

When should you see a doctor?

Most cases need no visit at all, but book one if:

• You are not sure what the rash is, especially if it looks like ringworm and antifungal cream has not helped.
• The itch is keeping you awake or does not respond to pharmacy treatment.
• The rash involves the palms, soles or mouth, or you feel unwell beyond a mild cold.
• You are pregnant.
• The rash lasts longer than 10 weeks, looks infected, or dark or light spots linger and bother you.

Taking a photo of the herald patch on the day you notice it, and of your back a week or two later, gives your doctor the full story even after the first patch has faded.