Anger causes immediate stress. It pumps in adrenaline and noradrenaline, which are chemicals for the fight and fight reaction. The problem comes when these chemicals are released at a situation that doesn't demand them, e.g. waiting at a doctor's reception. Anger opposes the release of hormones that have a calming and a soothing effect. This leads to stress arousal and all the disorders of stress that follow.
Anger takes away pleasure and love in life.
This leads to low brain serotonin level. Risky behavior like overeating, smoking and alcohol takes place to recover pleasure and raise brain serotonin level. Suppression of the immune system i.e. at the atomic level, the stress hormones attack the nucleus of the cell and change the structure of DNA, resulting in immune disorders like infections, allergies, cancer and auto immune disorders. Hostile people are lonely. They go to parties but cannot come out of their shell to mix with others.