Hemorrhoids are common colon problems that affect both men and women equally. Roughly half of the population has hemorrhoids by age 50. They can be internal (inside the anus) or external (under the skin around the anus), and occur when the veins around the anus or lower rectum become swollen and inflamed. Hemorrhoids are often caused by straining during a bowel movement. Other factors that can lead to hemorrhoids include things like pregnancy, aging, and chronic constipation or diarrhea.