Redspots is a common childhood disease similar to chickenpox.
The disease causes red dots to appear on the face and body and an itching which is soothed with salves.
Redspots is harmless to anyone under the age of ten and once one has it, they will be immune to it for the rest of their life. However, adults who do not contract it in childhood remain at risk for infection and may die from it.
A Feast for Crows
Princess Arianne Martell plots to have Princess Myrcella Baratheon crowned as queen. Rosamund Lannister has her hair curled so she can appear to be the princess, and Myrcella paints red dots on the handmaid's face. Ser Arys Oakheart informs Maester Caleotte of the supposed redspots, and the maester stays away because he never had the disease as a child.