Settlement bars Airborne from saying any of its products prevents colds unless it can back up claims with evidence

Airborne Health, makers of a top-selling product marketed as a cold prevention and treatment remedy, signed a $7m (£4.5) settlement on Tuesday to settle false advertising claims levelled by 32 state attorneys general and the District of Columbia.

The settlement bars the company from claiming that any of its products fights germs, treats cold symptoms or prevents colds, flu and infections unless it can back up those claims with "reliable and competent scientific evidence".

Airborne was not able to supply such evidence, according to Washington attorney general senior counsel Robert Lipson.

The Florida-based company also is barred from influencing where retailers display Airborne products, including its popular Airborne Effervescent Health Formula.

The company issued a statement denying wrongdoing. It said it settled the claims in order to "close the book on these legal and regulatory issues." It continues to market the product as a dietary supplement that "supports" the immune system.

In August, Airborne agreed to pay up to $30m to settle false-advertising accusations made by the federal trade commission and consumers in a private class-action lawsuit filed in California.

Despite the legal actions, online pharmacies and retailers continue to market Airborne products for cold prevention and treatment.

Some websites even advise consumers to "take at the first sign of a cold," language specifically prohibited by the agreement.

Lipson said those claims should soon be removed from websites and store displays as the company makes retailers aware of the settlement. The states' settlement requires Airborne to police third-party advertising of its products to the extent they become aware of false claims, he said.