Pityriasis Rosea Appearance and Causes

Pityriasis rosea is a common, self-limiting rash that typically affects healthy adolescents and young adults. The circular shape of pityriasis rosea lesions is often mistaken for ringworm.

The cause of the rash is largely unknown, although some studies suggest pityriasis rosea may be viral. It tends to affect people between the ages of 10 and 35 and occurs more often in the colder months. Only 2% of people will have a recurrence.

This article discusses pityriasis rosea. It explains how the symptoms of pityriasis rosea and differ from ringworm. It also covers the different variations of the pityriasis rosea and how it is diagnosed and treated.

Pityriasis Rosea Symptoms

Pityriasis rosea typically starts with an acute infection before the rash appears. Common symptoms include fever, headache, and sore throat. This is followed by:

• A "herald patch," a single, round, or oval lesion that usually develops on the trunk of the body
• Smaller, oval lesions that spread to the arms, legs, and face
• Occasional tiredness and aching

On lighter skin types, the lesions will appear salmon-colored; on darker skin, they will be more hyperpigmented (darker or patchy in color).

A pityriasis rosea eruption typically lasts between four and eight weeks. Symptoms may resolve as quickly as three weeks or persist for up to 12 weeks.

Pityriasis Rosea vs. Ringworm

Pityriasis rosea and ringworm can look similar, particularly with the herald patch that first appears with pityriasis rosea.

Both pityriasis and ringworm have round, itchy, scaly lesions. In both, a fine, tissue-like scale will typically be attached to the border of the lesion. However, there are key differences.

With pityriasis rosea, the rashes can spread over the back and limbs with a shape that resembles the outline of a Christmas tree with dropping branches. In contrast, ringworm can spread to different areas of the body, but not in the same kind of pattern.

Ringworm's rash may look normal in the center, giving it a "ring" appearance. Pityriasis rosea's herald patch may have an elevated border and a depressed center.

The two conditions may also differ in where they appear. Ringworm can affect any part of the body, including the fingers and toes. Pityriasis rosea lesions usually appear on the trunk of the body as well as the upper arms and legs, although there are exceptions.

Ringworm and pityriasis rosea also have different underlying causes. Pityriasis rosea is thought to be a viral infection, though the exact cause is still unknown.

Ringworm, also known as tinea, is a fungal infection spread through skin contact with an infected person or contaminated items. Pets can also carry the tinea fungus.

Pityriasis Rosea Variations 

Pityriasis rosea can appear differently in different people. In younger children, pregnant women, and people with darker skin, the rash will appear bumpier (papular). Vesicles and wheals can sometimes be seen in infants.

While pityriasis rosea typically develops on the trunk and extremities, some people have a rash covering the entire body. Lesions in the mouth are also known to occur.

Pityriasis Rosea Diagnosis 

Pityriasis rosea is typically diagnosed based on the appearance of the rash. At the same time, it is commonly misdiagnosed as other conditions such as psoriasis, nummular eczema, and syphilis.

Because the cause of the rash is still unknown, identification usually requires the exclusion of all other causes.

To do this, a KOH test and other laboratory assays will sometimes be performed to rule out ringworm and other fungal skin infections. Screening of sexually transmitted diseases may be used to rule out syphilis. In rare cases, a lesion may need to be biopsied.

Pityriasis Rosea Treatment 

Pityriasis rosea isn't thought to be contagious, so there's no need to avoid contact with someone who has it. Treatment options may be limited, however, given the slim understanding of the condition.

Recommended treatments include:

• Acyclovir: An anti-viral medication, acyclovir has been shown to relieve the severity of pityriasis rosea and reduce the length of the disease when taken five times a day at 400 to 800 milligrams. However, its effect on itch relief is inconclusive.
• Ultraviolet B (UVB) phototherapy: This treatment involves using fluorescent light tubes targeted to deliver ultraviolet radiation to affected areas. Studies found that it helped to reduce severity and symptoms when used multiple times a week for up to four weeks.
• Antihistamines: Your healthcare provider may also recommend oral antihistamines such as Benadryl (diphenhydramine) or Zyrtec (cetirizine) to relieve itching.
• Corticosteroids: Over-the-counter topical corticosteroids may be used two to three times a day for up to three weeks to reduce itching.

Other treatments that may provide itch relief include calamine lotion, cool oatmeal baths, and cold compresses.

Summary

Pityriasis rosea is a common rash that tends to occur in adolescents and young adults. The round scaly lesions resemble ringworm. However, the two conditions differ in where they appear and how they spread. The pityriasis rosea rash usually lasts about six to eight weeks.

Your healthcare provider can diagnose pityriasis rosea by appearance or by doing tests to rule out other infections. They may suggest treatment to help reduce symptoms, including anti-viral medications, ultraviolet B phototherapy, oral antihistamines, and topical corticosteroids.