Shampoo made with ionic silver, bottles of “free-radical quenchers” and a $2,995 device called the “photon genie” have all fallen foul of US regulators ­battling modern-day snake-oil marketing spawned by the ­global swine flu pandemic.

Almost half of the legal warning letters regularly issued to retailers and manufacturers by the US Food and Drug Administration since May have targeted fraudulent swine flu claims for more than 120 products, ranging from vitamin supplements and herbal teas to disinfectant sprays and home air purifiers.