What are the causes of employee stress?

Flu job descriptions , 

Discrimination , (based on  gender, age , beliefs , religion , race etc ) 

Destructive managerial feed backs , 

Not to be informed on future objectives of the company , 

The absence of performance management system , 

The presence of apparent nepotism in the company , 

The absence of work-life balance , 

The absence of success recognition 

The absence of "code of conduct " in the company , 

The absence of career progressing opportunities in the company .

Millions of reasons can cause stress to an employee.

Personal reasons related to his family, environment, traffic on the roads...

Work reasons related to the work environment like feeling not able to adapt to the work place.Also not fully understanding the work procedure can cause stress and fear of making mistakes.

Sometimes employees are irritated from their colleagues or their managers.

Work environment - Job stability - good treatment - continuous work pressure - Communicate

Agree with all

HSE has identified six factors that can lead to work related stress if they are not managed properly.

Demands: Employees indicate that they are able to cope with the demands of their jobs.

Control: Employees indicate that they are able to have a say about the way they do their work.

Support: Employees indicate that they receive adequate information and support from their colleagues and superiors.

Relationships: Employees indicate that they are not subjected to unacceptable behaviors, e.g. bullying at work.

Role: Employees indicate that they understand their role and responsibilities.

Change: Employees indicate that the organization engages them frequently when undergoing an organizational change.

I agree with the experts, no room to add on more.. Talking about stressful employees stresses me.. 

•      External causes

–     Family, work, economics, work, life changes, unforeseen events, etc.

•      Internal causes

–     Worry, uncertainty, fear, attitudes, unrealistic expectations, etc.

mouawad el-hajal's answer is good; I agree with him.