Good resistance ensures that your body offers resistance to viruses, bacteria, fungi and parasites.
When you have a low resistance, your immune system does not work properly. You are not able to cope with pathogens and therefore get sick quickly.
Your immune system includes white blood cells and lymph nodes. Your white blood cells render pathogens harmless. Lymph nodes ensure the production of extra white blood cells. When you are sick, your lymph nodes swell, this is because they are very active.
You can do quite a bit to give your immune system a helping hand for a good resistance. Avoid lack of sleep, poor nutrition and stress.