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Ajinomoto, a Japanese company, is not a household name in the West - but a product it makes, monosodium glutamate, is notorious.

Commonly referred to as MSG, the flavouring agent conjures up images of greasy meals followed by headaches.

Now Ajinomoto has launched a campaign to recover MSG's reputation by taking on an unlikely target - Merriam-Webster's Dictionary.

The publisher is being pressed to change "Chinese Restaurant Syndrome".

The dictionary entry is racist and unscientific, says Ajinomoto, and unfairly vilifies MSG.

A campaign video featuring Asian-American celebrities declaring that "MSG is delicious" and urging an edit has helped prompt the publisher to say it will reconsider.

What is 'Chinese Restaurant Syndrome'?

Tucked between "Chinese red" and "Chinese rose", the disputed entry in Merriam-Webster's is defined as:

"A group of symptoms (such as numbness of the neck, arms, and back with headache, dizziness, and palpitations) that is held to affect susceptible persons eating food and especially Chinese food heavily seasoned with monosodium glutamate."

It first appeared in the reference book in 1993, but entered American parlance decades earlier.

The etymology is traced to a 1968 letter that appeared in the New England Journal of Medicine claiming that Chinese food brought forth ailments.

The letter was uncovered to be a hoax, but the myth remains. The US Food and Drug Administration has long approved MSG for consumption, and studies have failed to show that the chemical causes the alleged "syndrome".

What's the science behind MSG?

The flavour enhancer works when molecules of MSG bind to receptors on the tongue that naturally sense the key flavour chemical it contains - glutamate.

Glutamate is a compound naturally found in foods from breast milk to parmesan cheese.

MSG was patented in 1909 by the Japanese chemist Kikunae Ikeda, who gave his invention the name "the essence of taste" and described its ineffable flavour as "umami", now recognised as one of the five basic flavours.

Although anecdotal claims that MSG has adverse effects have proliferated since the mid-20th Century, no studies have established any accepted mechanism for harm.

A 2019 review of scientific literature in the journal Food Science and Food Safety concluded that claims linking MSG to an assortment of ailments were unsubstantiated.

Words and meanings

The comedian and chef Eddie Huang and the TV host Jeannie Mai were recruited to bolster the MSG's cause.

"You know what gives me a headache? Racism," says Ms Mai.

The campaign theme fits within a larger movement to elevate ethnic foods, which chefs like Mr Huang have argued are unfairly seen as inferior to European fare.

Merriam-Webster's has said that it will consider revising "Chinese restaurant syndrome".