As we grow up, we become conscious of our own personal agenda and whenever another human being or an outside situation interferes with this agenda, we feel a subtle nuisance. Each time we experience this nuisance or anger, we release adrenaline which is an anger provoking chemical. Several thousand nuisances later, we have created a cause and effect response to these minor nuisances, like traffic jams, etc. Once this condition response is established, we believe that only aggressive behavior can achieve the desired result for e.g., the parent might give in to the tantrums of the child by agreeing to what the child wants, but the net effect is that the child has been rewarded for throwing a tantrum. As a result, he feels that to control a situation he needs to be aggressive.
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.