Mandy Moore shares 2-year-old son Gus has Gianotti-Crosti Syndrome

Mandy Moore is opening up about a family health scare.

The "This Is Us" alum took to social media to share an incident that landed her family in multiple doctor's offices on July 22. She revealed that she and husband Taylor Goldsmith's 2-year-old son Gus woke up that morning with an unexplained rash, and medical professionals were unable to immediately determine its cause.

"This sweet boy woke up with a crazy rash on Saturday am," Moore wrote alongside a picture of Gus on her July 28 Instagram story. "We tried to deduce what it could be and did anything to help him find relief from the itch."

She added that despite bringing Gus to a pediatrician, dermatologist and pediatric dermatologist, the young boy was all "smiles and laughs like the rockstar he is."

Thankfully, doctors were eventually able to identify the skin condition.

"Turns out it's a viral childhood rash that just spontaneously appears called Gianotti-Crosti syndrome," the 39-year-old wrote over an image of the toddler's legs covered in red splotches. "It's all over his legs and feet (ouch) and the backs of his arms but nowhere else."

See Mandy Moore's Newly Designed Room for Son Gus

However, the "Princess Diaries" actress revealed that Gus has a little bit of a healing journey ahead as the only treatment for the rash is Benadryl and steroid cream—and it could still last 6-8 weeks.

She finished the series with a reflection on motherhood, adding, "All of that to say, this parenting thing is weird and hard and sometimes you feel so helpless (and yes I'm ever so grateful it's only an itchy skin condition."

But she said she and the Dawes frontman are happy to take a cue from rockstar Gus, musing, "Kids are resilient and as long as he's smiling through it, we are a-okay."

In addition to Gus, the "Walk to Remember" actress is also mom to her and Goldsmith's 9-month-old son, Oscar a.k.a "Ozzie."

And with two boys aged two and under, she's shared that life at home isn't always easy.

"Somedays I feel like we're barely above water," Moore told E! News on the July 25 episode. "The potty training is intense, but we're slowly but surely getting there. I love that someone told me, 'It's not an event, it's a process.'"

And what makes it all a little easier is seeing the sweet bond between her boys—and especially the love Ozzie has for his older brother.

"He is enamored with his brother, it is really sweet," she revealed. "He just looks at him with awe and wonder all the time and is his biggest fan. No one makes him laugh more, smile more."