Pityriasis rosea is most likely linked to a viral trigger, especially reactivation of human herpesviruses HHV-6 or HHV-7, and may also involve temporary immune system changes, stress, or recent infections, although the exact cause is still not fully confirmed. It often begins with a single larger lesion called the “herald patch” because this is thought to be the initial skin reaction where the immune response first appears, and then the rash spreads as the immune system responds more widely across the skin over the next days to weeks. Pityriasis rosea is not considered highly contagious, and person-to-person spread is very unlikely. Risk factors may include recent viral illness, weakened or fluctuating immunity, stress, seasonal changes, and younger age (commonly 10–35 years), but it can occur in otherwise healthy individuals without a clear trigger.