Is that rash caused by chickenpox or measles?

While both chickenpox and measles cause rashes, they are different in appearance. Measles produces flat, red, blotchy rashes (seen here), while chickenpox starts with raised red spots that become fluid-filled blisters (see photo below). — Photos: Wikimedia Commons

Chickenpox and measles infections in children can look similar to one another, especially during the early phases of infection.

This can make it difficult for parents to distinguish between the two infections.