But not going to toilet when you need to is really bad. If you hold it in, it can cause all sorts of health problems that can hurt you later in your life, like bladder infections.
The researchers compared what kids in the UK and those in Sweden thought of the toilets in their schools.
Health specialists in other European countries suggest problems with school toilets is something affecting the entire continent.
It's not the first time school toilets have caused a stink. Last year, CBBC Newsround reported that bad toilets were the number one complaint for Welsh school pupils.