The Bahraini government rejected the criticism, saying its security forces conformed to international standards.
Activists say at least 30 people have died as a result of tear gas use in Bahrain since protests began last year.
Tear gas is a generic term for a group of at least 15 toxic chemical agents that disable people by exposing their lungs, skin and eyes to irritants. CS gas is the most commonly used by for crowd control.
‘Unprecedented’
The report published by PHR on Wednesday, entitled Weaponising Tear Gas, was based on interviews with more than 100 Bahrainis and evidence gathered by PHR’s investigators in April.
Its authors said the extensive and persistent use of tear gas against civilians by Bahrain’s security forces during the past 18 months was unprecedented in the 100-year history of its use throughout the world.
"Law enforcement officials have deployed this toxic agent to punish protesters, inflict suffering, and suppress dissent. Usually perceived by the public and security forces as a benign tool for crowd control, tear gas, especially when used in large quantities and in enclosed spaces, poses serious health risks and even causes death," they wrote.
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Suggestions that the use of tear gas in Bahrain is severely injurious or even lethal is simply not backed up by any research or proof”
Bahrain Information Affairs Authority
"Since February 2011, the Bahraini government has unleashed a torrent of these toxic chemical agents against men, women, and children, including the elderly and infirm."
The report said Bahrain’s majority Shia community, which has led the protests demanding reforms by the Sunni royal family, had suffered abnormally prolonged exposure.
This had led to significant increases in miscarriages and respiratory problems in areas where tear gas was used frequently, it added.
The report described instances in which non-protesters had tear gas fired into their cars or homes. In at least two cases, people died from complications related to exposure to tear gas because they were trapped in enclosed spaces, it said.
Civilians had also suffered serious wounds when their heads and limbs were hit by metal canisters fired at close range, the authors found.
‘Routine violations’
The report concluded that the authorities had "routinely violated every UN principle governing police use of force". It also said the methodical use of tear gas as a weapon to attack civilians inside their homes and cars flouted international human rights law, and constituted torture, cruel and inhuman treatment.
PHR called on Bahrain’s government to immediately end all attacks on civilians and suspend its use of tear gas while it conducted an impartial investigation into its misuse and held accountable those who had used the gas in excessive or improper ways.
The group also urged the government to disclose information about which toxic chemicals its tear gas canisters contained and permit scientists and health professionals to study the effects of prolonged tear gas exposure in the Gulf state.
The government rejected the report’s findings, saying it "denies and condemns the use of lethal force or unlawful means in controlling demonstrations".
"Any means that have been exercised by security forces adhere to international standards of riot control," a statement said.
"Suggestions that the use of tear gas in Bahrain is severely injurious or even lethal is simply not backed up by any research or proof."
The government promised improvements after an independent commission of inquiry found that security forces had used excessive force, torture and forced confessions when suppressing pro-democracy protests in February and March 2011.
In a separate development on Wednesday, police chief Tariq al-Hassan said three of the six men wanted in connection with a "bomb factory" discovered in June had been arrested.
