Colds can be caused by a low base immune system or by underlying diseases that affect the immune system. In addition, cold symptoms may also be allergic rhinitis and other non-cold diseases. 1. Low basic immunity: when the patient seriously lacks of exercise, long-term fatigue or malnutrition, the body’s basic immunity is low, and the ability to resist viruses decreases, so it is easy to catch colds again and again. 2. Existence of basic diseases that affect immunity: for example, diabetes, nephrotic syndrome, etc.. Serious ones include AIDS, in which the HIV virus destroys the body’s T-lymphocytes, which in turn leads to the destruction of the body’s immune system. In the face of viral invasion, the loss of resistance, so very easy to catch a cold. 3. Other diseases: such as allergic rhinitis, allergic rhinitis patients when exposed to allergens such as pollen, dust, animal hair and other stimuli, will cause the expansion of blood vessels in the nasal cavity, mucus glands secretion exuberant, resulting in runny nose and other symptoms. If you are extremely susceptible to colds, it is recommended that you go to the hospital to clarify the cause of the disease and follow the doctor’s instructions for treatment.