Helmets and mouthguards can prevent serious head and facial injuries, but there is no evidence they specifically stave off concussion, top authorities in sports medicine say.
Paradoxically, wearing this protection may lead to injuries because a player is tempted to take greater risks, they say.
Concussion has become a big issue in contact sports such as American football, ice hockey, rugby and football.
Writing in the British Journal of Sports Medicine, a panel of 28 neurologists say concussion is a complex phenomenon.
Symptoms may take just a few minutes or several hours to emerge, and recovery may take as long as 10 days -- in some cases even longer.
In skiing, snowboarding, cycling, motor and equestrian sports, where a player may fall on a hard surface, helmets can help prevent skull fractures and other forms of serious injury, the specialists say.
In addition, mouthguards "have a definite role" in stopping injuries to the face.
However, "there is no good clinical evidence that currently available protective equipment will prevent concussion," they add.
"Biomechanical studies have shown a reduction in impact forces to the brain with the use of head gear and helmets, but these findings have not been translated to show a reduction in concussion incidence."
There can also be a "paradoxical increase in injury rates" when players, kitted out in protective gear, adopt more dangerous tactics.
More than 3,700 former National Football League (NFL) players have filed lawsuits in the United States, accusing bosses of ignoring evidence about the long-term impact of repeated blows to the head.
The issue came to the fore after Junior Seau, considered one of the greatest linebackers of all time, shot himself dead in May last year at the age of 43.
A post-mortem examination of his brain revealed that, like dozens of former players, he was suffering from chronic traumatic encephalopathy, or CTE -- a degenerative brain disease.
The report -- a summary of a conference of concussion experts held in Zurich last November -- refuses to connect concussion with CTE, saying "a cause and effect relationship has not as yet been demonstrated."
It suggests sports supremos consider ways of bringing a player off-field for a concussion assessment without disrupting the flow of play and to think of appropriate rule changes.
In football, for instance, arm-to-head contact, when players leap up to head a ball, accounts for roughly 50 percent of concussions.