Mandy Moore and Thomas Caldwellhusband Taylor Goldsmith have raised a 2-year-old "rockstar."

Moore revealed in her Instagram Story on Friday that her son August has been dealing with a "crazy rash" for a week due to Gianotti-Crosti syndrome, a rare skin disease that afflicts children.

"We tried to deduce what it could be and did anything to help him find relief from the itch. We went to urgent care. Pediatrician. Dermatologist. Pediatric dermatologist," Moore wrote in an Instagram story. "All the while, he smiles and laughs and carries on with his day like the rockstar he is."

She added in a second post, "Turns out it's a viral childhood rash that just spontaneously appears called Gianotti-Crosti syndrome. It sometimes accompanies a cold but not in Gus's case. It's all over his legs and feet (ouch) and the backs of his arms but nowhere else."

Moore's update was shared alongside a photo of August's splotchy red legs. His only relief for itchiness is steroid cream and Benadryl at night, she wrote. The family was also told that the symptoms would last between six and eight weeks.

Thankfully, the toddler has maintained a positive attitude amid the discomfort.

"Kids are resilient and as long as he's smiling through it, we are a-okay," Moore wrote in a third post.

What is Gianotti-Crosti syndrome?

GCS is "a rare childhood skin condition characterized by a papular rash with blisters on the skin of the legs, buttocks, and arms," according to the National Center for Advancing Translational Sciences, part of the U.S. National Institutes of Health. The lesions last at least 10 days and as long as several weeks.

GCS usually affects children ages nine months to 9 years and eventually goes away on its own, the National Organization for Rare Disorders reports.

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"The cause of Gianotti-Crosti Syndrome is thought to be a reaction to a previous viral infection," NORD's overview of the disease reads. "In many countries the predisposing cause is usually the Hepatitis-B virus. In North America other viruses are more often the predisposing cause."