Why do we close our eyes when eating a lemon?

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Photo: veronka & cia (Getty Images)

Have you ever eaten a piece of lemon? If so, then you are aware that it is such a sharp flavor that just touching it to the tip of the tongue can be enough to set off the visible reaction. 

Closing our eyes or making funny faces when we taste something sour is often involuntary. That means we do it without trying. It may happen because we have an instinct not to eat things that are dangerous. Of course, not all sour foods are bad for us. But some sour foods can make us sick—spoiled milk or fruit that is not ripe, for example. Reacting with a wrinkled-up face may be our body’s way of trying to warn ourselves and others to stay away from foods that might hurt us.

According to another research, we probably got the reflex of closing our eyes from our ancestors. Our eyes are closed to prevent the sour lemon juice from getting into them, which might harm the mucous membranes.

How did our sense of taste evolve?

Over millions of years, our sense of taste evolved to help us choose which foods to eat. Choosing the wrong food could mean wasted energy, poor nutrition or poisoning from eating something that can do harm to our bodies. According to Current Biology Perspective on Food and Human Taste, humans relied on fruit and other plant-based foods and eventually developed a strong sense for the natural bitter taste in plants and leaves.

As time progressed, we retained these early taste preferences and acquired newer ones. We like the taste of sweet because it signifies a source of sugar, which means energy. We like sour because it is a source of vitamin C. Our bodies don’t produce vitamin C, but it is essential for survival. We like salty because our early plant-source diet did not have enough salt. That’s why animals that don’t eat meat (herbivores) seek out salt licks.

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