A 4-year-old Boy with Severe, Painful Rash

Watch this live video exam and hear details from the boy's mother about the acute, widespread eruption. What's your diagnosis?

A 4-year-old boy is seen for an acutely worsening rash over 2-3 days; mother describes blisters that ruptured leaving red, raw, peeling, painful skin lesions predominately on trunk and arms. Hx of  chronic severe eczema, environmental allergies. Tacrolimus, steroids in past; vaccinations up to date; oral acyclovir x1 day. Vitals, WNL.

What's your diagnosis?