Pityriasis rosea is a rash that usually begins as a large circular or oval spot on your chest, abdomen or back. Called a herald patch, this spot can be up to 4 inches (10 centimeters) across.

The herald patch is typically followed by smaller spots that sweep out from the middle of your body in a shape that resembles drooping pine-tree branches.

Pityriasis (pit-ih-RIE-uh-sis) rosea can affect any age group. It most commonly occurs between the ages of 10 and 35. It usually goes away on its own within 10 weeks. Pityriasis rosea can cause itching. Treatment may help relieve the symptoms.

Pityriasis rosea typically begins with a large, slightly raised, scaly patch — called the herald patch — on your back, chest or abdomen. Before the herald patch appears, some people experience headache, fatigue, fever or sore throat.

A few days to a few weeks after the herald patch appears, you may notice smaller scaly spots across your back, chest or abdomen that resemble a pine-tree pattern. The rash can cause itching, which is occasionally severe.

When to see a doctor

See your doctor if you develop a persistent rash.

The exact cause of pityriasis rosea is unclear. Some evidence indicates the rash may be triggered by a viral infection, particularly by certain strains of the herpes virus. But it's not related to the herpes virus that causes cold sores. Pityriasis rosea isn't believed to be contagious.

Complications of pityriasis rosea aren't likely. If they do occur, they may include:

• Severe itching
• On dark skin, lasting brown spots after the rash has healed

In most cases, your doctor can identify pityriasis rosea simply by looking at the rash. He or she may take a small scraping of the rash for testing, as this condition can sometimes be confused with ringworm (tinea corporis).

In most cases, pityriasis rosea goes away on its own in four to 10 weeks. If the rash doesn't disappear by then or if the itching is bothersome, talk with your doctor about treatments that can help. The condition clears up without scarring and usually doesn't recur.

Medications

If home remedies don't ease symptoms or shorten the duration of pityriasis rosea, your doctor may prescribe medicine. Examples include:

• Corticosteroids
• Antihistamines
• Antiviral drugs, such as acyclovir (Zovirax)

Light therapy

Exposure to natural or artificial sunlight may help the rash fade. Light therapy may cause lasting darkening in certain spots, even after the rash clears.

The following tips may help relieve the discomfort of pityriasis rosea:

• Take over-the-counter allergy medicine (antihistamines). These include diphenhydramine (Benadryl, others).
• Bathe or shower in lukewarm water.
• Take an oatmeal bath. You can find oatmeal bath products at your pharmacy.
• Apply a moisturizer, calamine lotion or an over-the-counter corticosteroid cream.

You're likely to start by seeing your primary care doctor. He or she may refer you to a doctor who specializes in skin disorders (dermatologist).

Here's some information to help you get ready for your appointment.

What you can do

• List any symptoms you're experiencing, including those that seem unrelated to the reason for which you scheduled the appointment.
• List key personal information, including any major illnesses, stresses and recent life changes.
• Make a list of all medications, vitamins and supplements you're taking, including the dosage information.
• List questions to ask your doctor.

For pityriasis rosea, some basic questions to ask your doctor include:

• What's the most likely cause of this rash?
• What are other possible causes for my symptoms?
• I have another health condition. Could it be related to the skin rash?
• Is this skin condition temporary or long lasting?
• Will this rash leave permanent scars?
• What treatments are available, and which do you recommend?
• Will treatment for the skin rash interact with other treatments I'm receiving?
• What are possible side effects of this treatment?
• Will the treatment help ease the itching? If not, how can I treat the itching?

In addition to the questions that you've prepared to ask your doctor, don't hesitate to ask other questions during your appointment.

What to expect from your doctor

Your doctor is likely to ask you questions about your symptoms and possible causes. Questions to expect include:

• When did you first begin to notice the rash?
• Have you had this type of rash in the past?
• Are you experiencing symptoms? If so, what are they?
• Have your symptoms changed over time?
• Does anything seem to improve your symptoms?
• What, if anything, appears to worsen your symptoms?