Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Hemorrhoids ?
    ### Response:
    Swelling in the anal or rectal veins causes hemorrhoids. Several factors may cause this swelling, including
                
- chronic constipation or diarrhea  - straining during bowel movements  - sitting on the toilet for long periods of time  - a lack of fiber in the diet

    