You know you have to rush to the ER and call your doctors right away when your chest hurts and you can’t breathe. These are signs you can’t ignore. But some insignificant symptoms that many would dismiss as the result of too much stress are in fact a way for your body to tell you to check your health.

Some conditions and diseases people have for some time — completely unaware — and it would be good to pay better attention to potential signs and symptoms. Most of us consider our habits as simply that — habits, sometimes bad. While most people grow out of different habits, like nail biting, not all do, or they suddenly develop a new one — and that could be a sign. Overlooking our habits might allow a disease or condition to go undetected.

You can sometimes smell if you’re ill. Many diseases have a particular odor. Diabetes, for example, can make your urine smell like a sweet fruit. One woman can even smell Parkinson’s. But not everyone has such a unique ability. Most people have to rely on what they know about what’s normal behavior. For example, drinking coffee in the morning is, but drinking more than three cups in the afternoon is not; and exercising every day is, but working out three times a day, seven days a week is not.

Many people already know that getting cravings even when they’re already full is a sign of junk food overconsumption, but an increased appetite when you just ate can also indicate diabetes. Some habits are hard to recognize as being a sign of a potential health problem, especially if they have been part of your daily routine for years. But it never hurts to pay closer attention.

To create a list of 16 habits that may be masking an underlying health problem, 24/7 Wall St. consulted doctors and reviewed scores of research papers and academic studies.

Click here to read about biting your nails and other habits that could be a sign of a serious problem.