Brodi Willard, from the US, explained that her son came home from school with hives - a rash that can appear anywhere on the body - and they appeared even more every time he scratched them.
After calling her paediatrician, Willard took her son into doctors and he tested positive for influenza B.
″[My son] has had no [other] symptoms,” Willard wrote on Facebook.
“No fever, no cough, and no runny nose. He only has hives. Please keep watch on your children so if they develop hives, please call the doctor. I have never heard of this symptom but it is obviously something to be on the lookout for.”
But are hives a common symptom of flu? Professor Kamila Hawthorne, vice chair of the Royal College of GPs, tells HuffPost UK: “Hives are not recognised as an early or late symptom of influenza, so I think what we are seeing here is an ‘anecdotal’ connection, as there is no scientific or medical evidence that the two are connected.
“Parents shouldn’t panic if their children have hives, but as they know their child best, if they are concerned about their child’s health, they should seek medical assistance or advice.”
Hawthorne says hives are “irritating but harmless” in themselves and will usually settle within a few days.
She adds: “They may sometimes be an initial symptom of a serious allergic reaction and if they appear to be worsening, or if their child becomes distressed, unwell or develops swelling around the lips and mouth, parents should urgently seek the advice of a healthcare professional.”
Hives - also called urticaria - can occur in adults or children. The rash is often itchy and sometimes feels like it’s stinging or burning.
“Urticaria occurs when a trigger causes high levels of histamine and other chemical messengers to be released in the skin,” the NHS explains. “These substances cause the blood vessels in the skin to open up, resulting in redness or pinkness, and swelling and itchiness.
“There are many possible triggers of urticaria, including allergens, such as food or latex, irritants, such as nettles, medicines, and physical factors, such as heat or exercise. Sometimes, a cause can’t be identified.”