There is now evidence that points to abnormal stress responses as causing various diseases or conditions. These include anxiety disorders, depression, high blood pressure, and cardiovascular disease, certain gastrointestinal diseases, some cancers, and even the process of aging itself. Stress also seems to increase the frequency and severity of migraine headaches, and episodes of asthma. There also is scientific evidence showing that people experiencing psychological stress are more prone to develop colds and other infections than their less-stressed peers. Overwhelming psychological stress (such as the events of 9-11) can cause both temporary (transient) and long-lasting (chronic) symptoms of a serious psychiatric illness called posttraumatic stress disorder (PTSD).