Anger is stress. Stress is the cause of mental and physical damage. The body releases harmful chemicals, cells are damaged, etc. This is why we have ques such as headaches, stomach aches, blurry vision, etc in the presence of stress.
HI All: So this is the basic Japanese concept of "Sanpaku" , when the individual is not ina proper relationship with his world or his body or his mind, he is "Sanpaku" and th emanifestations of that are;
more disharmony in spirit and discord with the world and the body withers...
I believe this at 100%. The more we keep inside, the more we get aggravated and sick afterwards. It was said by a medical professional, when we tend to keep things bottled up, we have more chances getting ill, like cancer and all. Anger can do so much to a person.