The famous magician Dynamo has opened up about how an invisible condition called Crohn's, which affects the digestive system, can make his day-to-day life difficult.
An invisible condition is one that you not would not know somebody has just by looking at them.
There are many kinds of these conditions and they can affect people's lives in lots of different ways.
It might mean somebody can't eat certain things or that they get tired more easily than others.
Newsround went to meet 11-year-old Bridget to find out more about how her invisible condition called lupus affects her life.