DBT distinguishes between primary emotions and secondary emotions. Primary emotions are basic initial reactions that come on very quickly and don’t involve any thinking. Secondary emotions are reactions to the primary emotions.

For example if someone bumps into us and we nearly fall over we may immediately feel surprise and fear. Anger may be alternative primary emotion for some people. A behavioural response may be to lash out, call the person an idiot and hit them. Then later a feeling of guilt and regret may come. This is a secondary emotion. A behavioural response for some people may be to cut themselves, leading to temporary relief, followed by further guilt and shame.

It is possible for a primary emotional reaction to set off a
limitless chain reaction of distressing secondary emotions interspersed with a series of undesirable behavioural responses.

Emotion regulation skills are aimed at preventing or circumventing these chain reactions driven by distressing secondary emotions. 

The emotion regulation elements are:
G5i. Recognising your emotions
G5ii. Overcoming the barriers to health emotions
G5iii. Reducing physical vulnerability to overwhelming emotions
G5iv. Reducing cognitive vulnerability
G5v. Increasing positive emotions