A heading ban in football training for children up to the end of primary school has been introduced with immediate effect in England, Northern Ireland and Scotland.
The new guidance has been issued following a study which showed former footballers were three-and-a-half times more likely to die of neurodegenerative disease.
The ban will only apply to foundation phase players and will only be introduced to football training rather than match play.
The English, Scottish and Northern Irish football associations issued a joint statement on Monday confirming changes.
Former Chelsea and Millwall footballer Tony Cascarino welcomes the changes:
The changes follow a study funded jointly by the associations into the risks of heading in the sport.
Researchers at the University of Glasgow found no evidence to suggest the practice was the cause of an increased prevalence of neurodegenerative conditions among footballers.
But the decision to update the guidelines has been taken to "mitigate against any potential risks", the FA said in a statement.
Some youth football teams had already made the decision to restrict heading balls:
Officials said the guidelines would only be enforced in training due to the "limited number of headers" which occur in youth matches.
FA chief executive Mark Bullingham said: "This updated heading guidance is an evolution of our current guidelines and will help coaches and teachers to reduce and remove repetitive and unnecessary heading from youth football.
"Our research has shown that heading is rare in youth football matches, so this guidance is a responsible development to our grassroots coaching without impacting the enjoyment that children of all ages take from playing the game."
The University of East Anglia is conducting research into the impact of heading on long-term cognitive function and has appealed for former footballers - both men and women - aged over 50 to take part in the SCORES project.
One to volunteer is ex-Norwich City star Jeremy Goss who told ITV News he wanted to know either way if he was at risk of developing dementia.
The three associations said the guidance had been produced in parallel with UEFA's medical committee, which is seeking to produce Europe-wide guidance later this year.
The updated Heading Guidance will see a "graduated approach" to heading in training for children between the ages of 11 and 15.
Irish FA chief executive Patrick Nelson said: "As an association we believe this is the right direction of travel and are confident it will be good for the game, and those who play it."
Scottish FA chief executive Ian Maxwell, said: "Scottish football has a duty of care to young people, their parents and those responsible for their well-being throughout youth football.
Mr Maxwell added: "The updated guidelines are designed to help coaches remove repetitive and unnecessary heading from youth football in the earliest years, with a phased introduction at an age group considered most appropriate by our medical experts.
"It is important to reassure that heading is rare in youth football matches, but we are clear that the guidelines should mitigate any potential risks."
The FA in Wales has said it is currently reviewing "mini football" - the version of the game for children under 11-years-old.
In a statement it said: "Any guidance on heading will form part of the recommendations from this review".