1.Age in young children and the elderly because the body is deficient in preventing infection and disease.
2.Drinking alcohol, smoking and / or taking certain medications. Such as immunosuppressive medicines Ma cancer ( chemotherapy ), which will be made to give the immune system to resist disease and infectiondiseases.
3.The condition of some Such as disease, emphysema, cancer, diabetes , heart disease, tooth decay and chronic kidney disease
4.trouble with health care such as undernourishment, deteriorating health, living in poorly ventilated area or living in air pollution area