A Swedish preschool has been criticized for banning its children from wearing striped and spotted clothing because the patterns give one of its teachers severe migraine attacks.

The preschool, in Gallivare, 710 miles north of Stockholm, imposed the ban in one of its areas three years ago. But recent complaints from a parent meant the unusual dress code got nationwide attention Thursday.

Myran preschool Principal May Norberg said the ban had never caused any problems. Until now.

Norberg said the parent complained that the ban prevented the children from wearing what they, or their parents, chose.

Norberg said the ban was imposed after a staff meeting three years ago. The teacher had complained about recurring migraine attacks when working with children wearing spotted or striped patterns.

"And so the (preschool) staff urged parents to dress their children in one-colored clothing," Norberg said.

Some researchers claim that striped, spotted or even checkered patterns can cause migraines since they affect the brain and the eye's visual impressions.

"They project a certain light and can be very disturbing," said Professor Lars Forsgren at Umea University.

Anita Israelsson, a spokeswoman at the Swedish Work Environment Authority, said the clothing ban, since it deals with people's work environment, does not violate Swedish law and is usually handled by individual workplaces.