pityriasis rosea不是过敏，致病原因未明，可能是病毒引起的．6-8周或更长些会好.

What causes pityriasis rosea?

No one knows what causes pityriasis rosea. Research shows that it is not an allergy. We also know that fungi (plural of fungus) and bacteria do not cause this skin disease. A virus may be the cause, but researchers have yet to prove this.

It is possible that a virus causes pityriasis rosea, but this skin disease does not seem to be contagious. It does not seem to spread from one person to another.

Learn more about pityriasis rosea:

• Pityriasis rosea
• Pityriasis rosea: Signs and symptoms
• Pityriasis rosea: Diagnosis, treatment, and outcome
• Pityriasis rosea: Tips for managing