'Helpless' Mandy Moore reveals 2-year-old son is diagnosed with skin syndrome

Mandy Moore is a concerned mom after her older son, Gus, 2, is diagnosed with Gianotti-Crosti syndrome.

Taking to her Instagram Stories Friday, the This Is Us alum revealed the skin condition began with a "crazy rash" last week that covered both his upper and lower limbs.

"This sweet boy woke up with a crazy rash on Saturday AM," Moore wrote over a photo of Gus, whom she shares with her husband Tayor Goldsmith. "We thought maybe an [eczema] flare? Poison oak? Allergy. We tried to deduce what it could be and did anything to help him find relief from the itch. Went to urgent care. Pediatrician. Dermatologist. Pediatric dermatologist. All the while, he smiles and laughs and carries on with his day like the rockstar he is."

In a follow-up story, the actress posted a photo of the toddler’s legs covered with an intense red rash and wrote: "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. There's nothing to do but a steroid cream and Benadryl at night. And it could last 6-8 weeks. Ooooof. Anyone else ever experience this??"

The Princess Diaries star confessed that the discovery was a reminder that "this parenting thing is weird and hard and sometimes you feel so helpless," noting that she was grateful her son was only experiencing an "itchy skin condition."

"Kids are resilient and as long as he's smiling through it, we are a-okay," she concluded.

According to WebMD, Gianotti-Crosti syndrome, also known as Acrodematitis is restricted to children and appears as an itchy, blistering rash.

"It's most common in children under the age of 9 years old, and children with underlying skin conditions like atopic dermatitis are also more likely to develop Gianotti-Crosti," as per the medical website.