Recurring colds and chronic infections are two common signs of a weakened immune system, according to Michael T. Murray, N.D., who operates the website DoctorMurray. Other symptoms of a weakened immune system include frequent cold sores or genital herpes and swollen and tender lymph nodes.
An abnormal mental state, diet, lifestyle and stress level can cause a weakened immune system, according to Murray. A weakened immune system not only means that a person will spend more time getting sick, but also that her immune system will continue to weaken and lead to chronic illness and disease.
According to Nancy Kalish of Yahoo Health, being overweight, consuming excessive sugar and not staying hydrated are some of the most common ways to depress the immune system and weaken its functionality. Long-term stress places a great burden on the immune system and can cause fluctuations that lead to an inability to fight infection and disease.
A healthy adult gets one to three colds per year, says Kalish. If a person picks up more colds than this or the typical cold lasts for more than three to four days, the chances are good that the immune system is not functioning at its top level.