Diseases of the immune system
If immune system-related diseases are defined very broadly, then allergic diseases such as allergic rhinitis, asthma, and eczema are very common. However, these actually represent a hyper-response to external allergens, according to Dr. Matthew Lau, chief, department of allergy and immunology at Kaiser Permanente Hawaii. Asthma and allergies also involve the immune system. A normally harmless material, such as grass pollen, food particles, mold or pet dander, is mistaken for a severe threat and attacked.