Research has shown younger players often do not have the same neck strength as seniors and are at a higher risk of injury.
A team at Edinburgh University is advising that youth players undergo tests to demonstrate they have the necessary neck strength before being approved to play adult rugby.
They tested the physical strength of adult players from amateur leagues and under-18 front row players and found that despite looking as strong as their senior counterparts, the youths' lesser strength and fatigue endurance put them at a "significant disadvantage".
Dr David Hamilton, a researcher in the department of trauma and orthopaedics, said: "In the test group of high-performance under-18 group players, only two out of 30 players recorded the average neck strength of the adult group."
The findings have been welcomed by Scottish Rugby, which assisted with the study aimed at helping reduce injuries among school-age players.
Scrums are responsible for a significant proportion of spinal injuries, but the national rugby body has already adopted new guidelines which have seen the serious injury rate fall.
Professor of orthopaedic surgery Hamish Simpson said: "Our results showed that although under-18 players were as strong as the adults in general, they were unable to generate the same neck muscle force as adult players.
"It is likely that weak necks are a risk factor for the scrum collapsing - an event associated with serious neck injury risk. To ensure the safety of all six front-row players, it is essential that they are all strong enough to compete safely."
Dr James Robson, Scottish Rugby's chief medical officer and doctor on the past six British & Irish Lions tours, said: "This study suggests that youngsters can achieve peripheral strength. However, the key area for us is the strength of their neck and it would appear it's very difficult to attain 'adult-type strength' in this particular area.
"This research is helping to underpin our safety policies. It validates our stance on where and when we allow under-18s to play in senior rugby."
The study was funded by Edinburgh University and appears in the British Medical Journal.