A blocked anal gland, a sexually transmitted infection (STI), or an infected anal fissure can cause anal abscesses. Some other risk factors include:

Crohn’s disease or ulcerative colitis, which are inflammatory bowel diseases that cause the body to attack healthy tissue
diabetes
a compromised immune system due to illnesses like HIV or AIDS
anal sex, which can increase the risk of anal abscesses in both men and women
use of the medication prednisone or other steroids
current or recent chemotherapy
constipation
diarrhea

Toddlers or children that have a history of anal fissures (tears in the anal sphincter) are also at a higher risk for developing anal abscesses later on. Such anal fissures might occur in children who have a history of constipation.