If you have a cough when you have a cold, eating oysters may aggravate the cold. Although oysters are very nutritious and have a high protein content, as an aquatic shellfish, it is salty and cold in nature, which has a water-consuming effect on the organism, and is particularly dehydrated when you have a cold and cough. But when you have a cold, you are already thirsty, and to get well when you have a cold, you have to sweat by taking in a lot of water or expel phlegm when you cough, so eating oysters at this time not only competes with the cold for water, but also those undigested proteins are prone to produce phlegm.