Question

why the taste of food changes when a person has a cold

Answer 1

because There are nearly 100 rhinoviruses that cause more than half of colds, says Dr Marvin Hsiao, medical virologist at the University of Cape Town’s Department of Clinical Laboratory Sciences. He remarks that typical signs of a cold include nasal stuffiness, sore throat, sneezing, headache, cough and mild body aches.

Now count yourself lucky if you only have a cold and not flu, which is far worse and can make you feel as if you need to have your coffin measurements taken. 
“Severe flu symptoms (like high fever, weakness, fatigue, body aches and headache) often last five to seven days, while the worst of a cold is usually gone in two to four days,” comments Dr Hsiao.

Answer 2

So the cold merely blocks our nose and the sense of smell but along with it our ability to taste food goes to a toss. Fever changes the way we taste food..... You avoid food because it tastes bland and flavor less because of what the cold has done to your taste buds.

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