Your mother probably told you to always bring a sweater when it was chilly outside, but her advice can apply to when you’ll be spending time in the chilly indoors as well.

Even though over the summertime you would probably prefer to wear the least amount of clothes as possible to stay cool in the heat, it’s a good idea to always bring a sweater with you, according to Professor Ron Eccles of the Common Cold Centre at CardiffUniversity in Wales.

That’s because despite the high temps outside, most buildings jack up the A/C to compensate. Exposing your body to polar opposite extreme temperatures can lead to illness.

This is because our bodies are programmed to maintain a temperature of about 98 degrees Fahrenheit. So when outside, our bodies sweat to maintain the equilibrium and when we enter a cold building, we shiver to increase body heat.

As the body struggles to maintain its ideal temperature, blood vessels start to constrict particularly in the nose and throat—where viruses gravitate. Meanwhile, as the blood constricts, fewer white blood cells are produced, thereby decreasing the immune system and the ability to ward off infections.

If you have to go in and out of cold temperatures frequently, Professor Eccles suggests limiting time in the heat to just a few minutes so that the body does not have time to adjust to the difference.

Also, putting on a sweater in the cold temps helps your body not have to adjust either.

For more information, find the entire story here.