Increasing pressure on the tiny veins of the anus and rectum (anorectal veins) causes hemorrhoids. Pressure in the abdomen which transmits pressure to the anorectal veins is a primary cause. But many things can bring out or aggravate hemorrhoids including:

• Sitting or standing for long periods of time (which can cause hemorrhoids to swell or be pushed out)
• Constipation (which causes straining at bowel movements)
• Diarrhea
• Exertion (such as lifting and coughing)
• Being overweight
• Pregnancy and childbirth